Underwater Technology Vol 33 No 1

Marine Renewable Energies Special Issue

July 2015

A Personal View

New roles for underwater technology in the fight against catastrophic climate change
P Wadhams

Technical Papers

MSLED: The Micro Subglacial Lake Exploration Device
AE Behar, DD Chen, C Ho, E McBryan, C Walter, J Horen, S Foster, T Foster, A Warren, SH Vemprala and JM Crowell

Abstract: Satellite altimetry and ice-penetrating radar have shown the existence of active subglacial lakes in Antarctica which may have a significant impact on the Southern Ocean and the dynamics of the overlying ice sheet. Understanding how subglacial floods affect ice dynamics is imperative to predicting the effect of ice sheets on rising sea levels, but it is not clearly understood. Furthermore, these encapsulated lakes contain uncharacterised biological ecosystems and serve as analogue environments for future extraterrestrial exploration. To investigate these subglacial environments, the authors developed the Micro Subglacial Lake Exploration Device (MSLED), a unique highly-miniaturised remotely operated vehicle. Equipped with a high-resolution imaging system, as well as conductivity, temperature and depth sensors for in situ measurements, the MSLED is capable of determining geological, hydrological and biological characteristics of subglacial lakes. It was successfully deployed in Antarctica during the 2011–2012 and 2012–2013 Antarctic summer seasons in collaboration with the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) expedition to Subglacial Lake Whillans (SLW), contributing to the discovery of microbial ecosystems within these environments. The present paper outlines the scientific background behind the mission, the design and implementation of the MSLED, as well as the results of tests and initial deployments in Antarctica.

Review of pressure coring systems for offshore gas hydrates research
K Abid, G Spagnoli, C Teodoriu and G FalconeAbstract: In the subset of unconventional natural gases, shale gas, tight gas and coal bed methane are now being produced to some extent, whereas the biggest part of the unconventional resource is made up of gas hydrates which are still in the exploratory phase of development. It is recognised that the resource potential of gas hydrates existing in the Earth is twice the amount of the combined remaining resources of other fossil fuels (i.e. coal, oil and natural gas). So far, hydrates have been recovered using pressure coring carried out by vessels using conventional drilling methods. Original attempts to recover hydrates were based on upgrading underwater drill rigs with autoclaves. The present paper reviews the importance of pressure coring systems with the objective of assisting researchers and engineers in the development of technologies that will support the exploration of gas hydrates and to consider underwater drill rigs as novel drilling tools.
Multi-AUV target searching under ocean current based on PPSO and velocity synthesis algorithm
X Cao, D Zhu and SX YangAbstract: One of the challenges for underwater target searching by multi-autonomous underwater vehicles (AUVs) is ocean currents. During the search process different types of ocean currents may impose a negative effect which lengthens search paths and causes more energy consumption. In order to solve this problem, the proposed algorithm in the present paper combines the potential field-based particle swarm optimization (PPSO) and velocity synthesis algorithms. The goal is to control a team of AUVs to search for a target, while guaranteeing that each AUV’s motion can offset the impact of ocean currents. Firstly, the fitness function of particle swarm optimization (PSO) was determined by the potential function of the workspace; then, PPSO planned the reasonable paths iteratively; and lastly, the velocity synthesis algorithm kept the AUVs on their planned tracks to offset the influence of ocean currents by adjusting the AUV movement directions. Through simulation studies it was shown that the proposed algorithm is capable of offsetting constant as well as variable ocean currents with higher work efficiency and less energy consumption. 

Interface management of subsea field development
S Yasseri

Abstract: An interface refers to any logical or physical relationship required to integrate the boundaries between subsystems or between subsystems and their environment. The present paper combines a systems engineering (SE) approach and design structure matrix (DSM) for the interface management of the subsea production systems in the design, fabrication and installation phase. Strategies needed to manage interfaces between various subsystems and their execution and integration with the operational environment are discussed. It is suggested that a better way to keep a record of interfaces is by using a DSM, which is an N × N square matrix representing relationships between the system’s components. In this matrix, N is the number of components of the system. This matrix, which is constructed in a spreadsheet, provides a systematic approach to visualise, recognise, define, tabulate, store and analyse interfaces. The method is illustrated using a typical subsea production system. This approach also allows the identification of change propagation paths.

Technical Briefing

The validation of flexible pipes and risers

JHA Baker and D Liddle
Abstract: This paper presents the main discussion during, and findings from, a symposium of the same title held in St Andrews, Scotland, in October 2014. Overall, there is good understanding of flexibles but a number of opportunities for improvement are identified. This paper presents a schematic of the road map developed by the delegates for improvement of methods, practices and tools to enhance the validation of flexible pipes and risers.

Book Reviews

Commander Crabb – What Really Happened? by John Bevan
Reviewed by G Anthony

Offshore Safety Management: Implementing a SEMS Program, Second Edition by Ian Sutton
Reviewed by Prof C Kuo

The Science of Diving: Things your instructor never told you Edited by Constantino Balestra and Perter Germonpré
Reviewed by MDJ Sayer

Underwater Technology Vol 33 No 3

March 2016

A Personal View

Outlook for the wave and tidal stream industry in the UK
S Merry

Technical Papers

A method to improve instationary force error estimates for undulatory swimmers
Jeffrey A. Tuhtan, Gert Toming, Toomas Ruuben and Maarja Kruusmaa
Abstract: Our aim is to improve the analysis of the force dynamics common to experimental investigations of oscillatory locomotion in underwater research. This paper proposes a new method for instationary force error modelling and correction, calibrating on a passive body at laboratory scale. The calibration function is applied to instantaneous force estimates during undulatory swimming under turbulent flow conditions. The main advantage of this method is automated phase shift correction. This study uses a force plate to directly obtain the instantaneous streamwise and lateral forces on a passive and actuated fish robot under turbulent flow conditions. Force estimates are simultaneously obtained using the momentum deficit method, coupled for the passive case using a linear transfer function. The resulting instantaneous error model is evaluated in three turbulent flow experiments, during which the robot is actuated to mimic a swimming fish. Mean, median and modulo general linear transfer functions are evaluated to determine the best performing general function. Actuated instantaneous force estimate errors are reduced by 64%–93% in the streamwise and 75%–91% in the transverse directions. It was found that all three transfer functions had similar performance, considering the instationary force estimates during actuation. The modulo function performed best for the passive case.

Review of developments in lithium secondary battery technology
G Griffiths

Abstract: Lithium batteries power an increasing range of devices subsea in defence, industrial and scientific applications. Future installations will require batteries with greater energy and power capacity, of lower weight for use in underwater vehicles, at lower cost and with less risk of catastrophic failure. With these goals in mind, developments in lithium-ion and lithium metal secondary cells are reviewed. For lithium-ion, the state of the art in commercial cells and areas of promising research for the cells’ components – namely the anode, cathode, electrolyte and separator – are assessed for future improvements in performance and safety. New cathodes are most likely to provide incremental performance gains for lithium-ion cells. Heat-resisting or early-warning separators and novel electrolytes are set to reduce the likelihood and consequence of thermal runaway. Recent advances with ion-conducing surface coatings for lithium metal anodes are leading to practical high-capacity lithium sulphur secondary cells with good, and improving, cycle life. Aspects of these cells’ operating principles, including the polysulphide shuttle and high flashpoint electrolytes, contribute to cell safety. Further developments in acceptance testing and online monitoring of lithium batteries can also lead to greater safety.

A fresh initiative on the use of daylight magnetic particle inspection for the inspection of underwater steel structures
Ken Woolley, Tim Woolley and Bruce Banfield
Abstract: Underwater magnetic particle inspection (MPI) was a common non-destructive testing (NDT) method in the early days of North Sea oil and gas development (in the 1970s/early 1980s). It was primarily used to find cracks in nodal welds on offshore structures.
Underwater MPI was carried out using fluorescent inks, which were visible under ultraviolet (UV) light and had to be carried out in the hours of darkness. This led to lengthy and costly inspection programmes, as the inspection work was generally done during the summer months, with perhaps only 4 h of darkness in the northern North Sea.
The use of underwater MPI declined from the late 1980s for about 25 years but is now making a comeback. As offshore structures age and exceed their original design lives, the spectre of fatigue cracks has led to the need for detailed node weld inspection.
During the last 25 years, MPI inks have changed. Although they conform to the relevant international standards, these standards are for topsides use and thus not necessarily applicable to underwater conditions.
Recent trials have been conducted to determine the suitability of available inks to increasing white light levels underwater. This paper presents the work and discusses the findings, which have application worldwide.Spatially and temporally dispersed marginal subsea field valuation. Part I: preliminaries
S Yasseri
Abstract: This is part one of a two-part paper on the economic valuation of spatially and temporally distributed marginal subsea fields. Risks in subsea marginal field development arise from many sources, including the state of technology, oil and gas price, site condition, fiscal policy and regulations. Economic evaluation provides a valuable insight in how to improve the viability of a marginal field. Part I discusses the traditional methods of valuation, and then describes how the real option (RO) valuation can be applied for the valuation of scattered subsea reservoirs. None of the fields are large enough to justify the capital investment for individual exploitation. In Part II, these methods are applied to a case study and the relative merits of methods are discussed. It is argued that RO valuation enables the determinants of successful development to be identified.

Spatially and temporally dispersed marginal subsea field valuation. Part II: valuation
S Yasseri
Abstract: Risks in developing of subsea marginal fields arise from many sources, including state of knowledge, site, regulations and fiscal policy. Part I of this two-part paper (Yasseri, 2016) described three primary valuation methods, i.e. discounted cash flow, decision tree and real option, that can be utilised to examine risks and success factors so that the determinants of successful developments can be identified and reinforced. This paper (Part II) applies those three valuation methods to the scattered subsea field example described in Part I. This paper compares and contrasts these valuation methods, and highlights their relative merits as a decision-making support tool.

Book Review

Out of the decompression matrix by Bob Cole
Reviewed by MDJ Sayer

Underwater Technology Vol 33 No 4

July 2016

A Personal View

Plus ça change

            I Gallett

Technical Papers

Simulation of oblique propeller flow including cavitation and pressure pulses
E Güngör* and I˙. Bedii Özdemir

Abstract: In this paper, the performance of an inclined propeller in both non-cavitating and cavitating conditions was investigated using a finite volume based solver. The results were compared with the experiments conducted at the Potsdam Model Basin (Germany) (Barkmann et al., 2011; Kinnas et al., 2015). The propeller in the experiments was operating in an inhomogeneous flow and, therefore, the characteristics were deeply influenced by the inclination angle. Therefore, the present work includes both design and off-design conditions and simulations in a pull configuration. The sliding mesh technique was used to implement the rotations in the unsteady Reynoldsaveraged Navier–Stokes (URANS) solver, with the renormalisation group (RNG) k- e turbulent model. The effects of models for acoustics and cavitation phenomena were of particular interest and, therefore, multiphase mixture model was used as a cavitation model in which Rayleigh-Plesset equation describes the growth of a single vapour bubble in a liquid. Also, the Ffowcs–Williams and Hawkings (FWH) and direct methods were compared by predicting pressure pulses at receiver locations. The analysis involved visual observation of the cavitation pattern, in that there was a good agreement between the numerical predictions and the experimental data. The pressure fluctuations at different locations were also compared with the experimental data for both cavitating and non-cavitating cases. In the non-cavitating case, the amplitudes of the pressure fluctuations were in agreement with the experimental data, but those of pressure pulses in the cavitating condition were underpredicted. The spectral analysis of calculations also revealed the weak third harmonic observed in the experiments. The FWH approach produced good results in the spectrum of rotating propeller and, therefore, instead of the direct method, the FWH approach is recommended in such complicated cases as pressure pulse and cavitation. However, more advanced method is required to extend the work for better representation of bubble dynamics.

A measure of subsea systems’ readiness level
Sirous F. Yasseri

Abstract: Systems readiness level (SRL) is a metric for assessing progress in developing major subsea systems. SRL methodology builds on technology readiness levels (TRLs), developed by American Petroleum Institute (API) 17N to assess the readiness of subsea components for insertion. To estimate the level of readiness of a system comprising multiple components in their current state, SRL combines the TRL of each component with another metric called the integration readiness level (IRL). This metric expresses the readiness of each of these components to be integrated with other components of the system. An averaging approach is then used to estimate an overall level of systems readiness level if these components were to be used. This paper presents a distillation of experience gained in applying the readiness metrics to subsea systems by the author and others. The methodology for determining the progress of a typical subsea system development, using TRL, IRL and SRL metrics is illustrated using a typical subsea system.

Technical Briefing

Supporting renewable energy projects using high resolution hydrographic and geophysical survey techniques, Garden Island, Western Australia
Dr Peter Ramsay, Warwick Miller* and David Murrell

Abstract: With increasing public awareness on climate change issues and increasing pressure on governments to expand renewable energy programmes, the time appears optimum for the development of new marine renewable energy technologies and programmes. Carnegie Wave Energy is an Australian Securities Exchange (ASX) listed company that has developed and patented the CETO wave energy technology over the last 10 years. This technology is designed to convert the oscillating motion of ocean waves into zero-emission renewable power. The CETO technology has the added advantage of producing desalinated freshwater as a byproduct, making this a truly green energy technology. Marine GeoSolutions was contracted by Carnegie WaveEnergy to undertake a geophysical site investigation of potential deployment sites offshore of Garden Island for the installation of the planned CETO six power generation arrays and the cable route that would connect the arrays to the hinterland. While the geophysical site investigation employed standard off the shelf (OTC) survey technology to achieve these objectives, the purpose of this paper is to demonstrate how important renewable energy projects can benefit from the careful and skilful application of hydrographic and geophysical survey technologies. The geophysical survey programme included the simultaneous acquisition of multibeam bathymetry, sidescan sonar, magnetic profiling and sub-bottom profiling data. The true benefit of the geophysical survey, however, was achieved through the application of careful and meticulous data processing techniques by a small group of dedicated individuals to produce a set of high resolution survey products. This was achieved by careful combination and rendering of all the datasets to arrive at a comprehensive 3D geographic information system (GIS) data model that provides valuable insights into the physical environment in the areas of interest.

The Teredo worm and subsea umbilicals: risks and recommendations
Larry Parkes* and Alan Keeble

Abstract: The Teredo worm is a bivalve mollusc that is well known for its destructive  activity caused by boring into woods underwater. It can also damage subsea cables   and many cable designs incorporate anti-Teredo protection. The Teredo worm is an alien species to many marine environments, but its distribution is increasing. It is, therefore, possible that subsea umbilical failures, specifi cally in relation to power and/or communication transmission in the oil and gas industry, that have previously been fully or partially attributed to Teredo activity, may increase in the future. This paper reviews some methods of detecting impending Teredo-related umbilical failure and makes recommendations for future subsea umbilical design.

Book Reviews

Diving and Subaquatic Medicine, 5th edition By Carl Edmonds, Michael   Bennett, John Lippmann, Simon Mitchell
Reviewed by Dr Oliver Firth

Intelligent Autonomy for Unmanned Marine Vehicles By Carlos C Insaurralde
Reviewed by Dr Sanjay Sharma

Underwater Technology Vol 32 No 1

Marine Renewable Energies Special Issue

March 2014

A Personal View

Marine renewable energy: could environmental concerns kill off an environmentally friendly industry?

S Merry

Technical Papers

Control strategies for oscillating water column wave energy converters

K Freeman, M Dai and R Sutton

Abstract: The oscillating water column wave energy converter (OWCWEC) is an established device which produces electricity by causing an ocean wave to drive air through a turbine.
A system to control the operation can improve the device’s performance. In varying sea conditions, different objectives for control may be appropriate. For example, in some seas the controller might shut off the plant because the waves could damage the structure, while in others the controller should operate purely to maximise the energy passed to the electricity grid. The fundamentally nonlinear dynamics of the OWC–WEC influence the choice of control algorithm for the WEC.
Different outcomes in performance may be caused by very small changes in controller action. This is especially true for those OWC–WECs whose characteristics include stalling under certain conditions for optimal performance.
Robustness to uncertainty in inputs and prevention of damage to the structure are necessary. However, too much conservatism will lead to unnecessarily low extracted powers.
In the present paper, the advantages and disadvantages of feed-forward controllers and artificial neural networks previously used on OWC–WECs are discussed, as well as the testing of model predictive control and fuzzy logic controllers in the OWC–WEC context.

Coastal shelf model of northern European waters to inform tidal power industry decisions: SMARTtide

SE Bourban, SJ Couch, A Baldock and S Cheeseman

Abstract: Renewable energy extraction from tidal range and/or tidal current technologies in a particular area will affect the hydrodynamics of the local tidal system differently, impacting the tidal resource at the particular site. There may also be a regional effect on the hydrodynamics, affecting other tidal energy extraction schemes’ resource and potential energy yield. The impact of large–scale and/or widespread tidal energy extraction on the tidal energy resource is therefore important to understand in order to inform optimization and management of the UK tidal resource.
The present paper discusses a new tool that has been developed to provide capabilities for pre-feasibility assessments of energy extraction. The tool is called SMARTtide and is based on the 2D module of the open source TELEMAC system, a finite element shallow water solver.
The underlying northern European shelf model behind SMARTtide was commissioned and funded by the Energy Technologies Institute with the overall aim to assess interactions of tidal power energy extraction around the UK. Black & Veatch, HR Wallingford and the University of Edinburgh completed the project. The SMARTtide model comes with various levels of resolution available, including:
• the detailed continental shelf model (DCSM), with 200m resolution at the coast and sites of interest; and
• the coarse continental shelf model (CCSM), with 1km resolution at the coast and sites of interest.
Depending on the energy extraction scenario envisaged, simulation for a representative 15–day spring-neap tidal cycle takes on average less than 2hr for the detailed model and less than 1hr for the coarser model on a supercomputer (nine 12-core processors and one 12-core processor,respectively), which can be seamlessly accessed via a webinterface.

Energy from tidal streams: engineering issues, state of the art and future prospects

P Fraenkel

Abstract: The present paper aims to discuss some of the key design issues facing engineers developing tidal turbines and considers the advantages and disadvantages of different designs currently under development. Some detail on the general state of the art and the potential market for this technology is also given

Regulating marine renewable energy development: a preliminary assessment of UK permitting processes

G Wright

Abstract: While the UK has implemented a number of reforms to permitting processes to support the emerging marine renewable energy industry, research into the effectiveness of such reforms has been limited. The present paper presents a preliminary assessment of two key aspects of the UK’s regulatory framework: the seabed leasing process and the permitting process. In particular, the Crown Estate seabed leasing process and Scotland’s ‘one–stop shop’ for permitting are discussed. Some concluding thoughts are given regarding the efficacy of these processes, laying the foundation for further research and analysis

Technical Briefing

FP7 EU funded CORES wave energy project: a coordinators’ perspective on the Galway Bay sea trials

R Alcorn, A Blavette, M Healy and A Lewis

Abstract: The present paper gives an overview of the lessons learnt from the project called Components for Ocean Renewable Energy Systems (CORES). In the context of this European funded 7th Framework Programme research project, new components and systems for ocean energy devices were developed and trialed. The present paper also details the work packages, major achievements, significant impacts, summary results and the outcomes of the sea trials.

Book Reviews

Electricity from Wave and Tide: An Introduction to Marine Energy, by Paul A Lynn

Reviewed by Ray Hunter

Renewable Energy, Second Edition, by Andy McCrea

Reviewed by Rose Norman

Underwater Technology Vol 32 No 2

July 2014

A Personal View

How deep is the ocean – How high is the sky?
L Ayling

Technical Papers

Full-scale manoeuvring trials for the Wayamba unmanned underwater vehicle

D Sgarioto and C Madden

Abstract: The present paper outlines a new method to acquire experimental data for validating simulation models of highly manoeuvrable unmanned underwater vehicles (UUVs). Full-scale manoeuvring trials have been performed with the Defence Science and Technology Organisation’s (DSTO) Wayamba UUV at Corio Quay, Geelong. These manoeuvres are based on the International Maritime Organization (IMO) standards for ship manoeuvring, but have been adapted for application in a wide range of UUVs, including novel flatfish designs. The manoeuvring trials undertaken included straight-line speed tests, acceleration/deceleration tests, static turn tests and a variety of directional zigzag tests. In addition to representing a baseline dataset for investigating how design or configuration changes impact vehicle manoeuvrability, the data collected from the full-scale manoeuvring trials also showed them to be well suited to simulation model validation. Details of a DSTO-developed, MATLAB®-based model of the vehicle used for investigating low-level vehicle dynamics and performance are also provided. The representativeness of this model was demonstrated by comparing the model to a subset of the manoeuvring trial data. The manoeuvring trial results also provided some interesting insights relating to Wayamba’s manoeuvring performance, such as the vehicle’s initial turn bias and the efficiency differential between its main thrusters.

Technical Briefing

Book reviews

Underwater Technology Vol 32 No 3

November 2014

North Sea talents – Today and the next generation

C Milner

Technical Papers

Function selection among popular dive computer models: A review and proposed improvementsA Schuster, P Buzzacott, S Reif, B Kuch, A Gerges, E Azzopardi, MDJ Sayer and A Sieber

Abstract: For optimal safety a dive computer should be easy to use and the displayed information easy to understand. The present study examines the usability of dive computers and potential technologies to enhance safety. It should be noted that even if the ease of use of a dive computer is increased to an extent where it is intuitive to use, this does not release the diver from the recommendation to read the dive computer manual to safely dive with it.

For the present work, 47 dive computer models by 14 manufacturers were purchased and the manuals of another three were studied. Function selection was noted for each model. Where selection required a combination of long and short pushes, or more than one button, it was considered necessary to read the instruction manual merely to modify settings in the dive computer.

The mean number of buttons, switches or contacts per dive computer was 3.3 (SD 1.1, range 1–7). Twelve models (24%) did not have multiple functions per button, one model (2%) had a single multi-function and 36 models (72%) had multiple multi-functions per button. Accessing these functions required short or long push combinations. In 41 out of 50 (82%) of the dive computer models, the user interface was not intuitive.

Abstract: Optical wireless communications (OWC) are being considered for use under water because sea water exhibits a window of reduced absorption in the visible spectrum, particularly between 400–550nm. Recent technology has demonstrated the ability to support mid-range links (<200m) and at high bandwidths (<1Gbps) in clear oceans. The present paper outlines the governing transmission characteristics and reviews current experimental research in underwater OWC, highlighting the importance of the local chlorophyll concentration, particulate concentration and the resultant wavelength selection. Ideal wavelengths are found to be from 430nm, which represents a deep blue colour, to beyond 550nm in areas where the chlorophyll concentration is high.

Experiment of free-falling cylinders in water

Abstract: Trajectory of objects falling into water and their landing point and orientation are of interest for the protection of oil and gas production equipment resting on the seabed. Falling of small-scale model cylinders through water with low velocity has been investigated experimentally. Several experiments have been conducted by dropping model cylinders with the density ratio higher than 1 into a pool. The main objectives were to observe the trajectory and the landing point. Similar experimental results published by other researchers are reformulated to give common normalised landing points, which were then used to compare with the author’s tests.

Technical Briefings

Abstract: The present paper applies the threat matrix, developed for the integrity management of offshore oil and gas systems, to address reliability and maintainability requirements for a typical wave or tidal energy device. It includes some comparisons with oil and gas subsea infrastructure. The aim is to ensure a realistic assessment of life cycle maintenance requirements and life cycle costs.

Book Reviews

Subsea Optics and Imaging Edited by John Watson and Olive Zielinski

Reviewed by Gavin Anthony

Underwater Technology Vol 30 No 1

Summer 2011

A Personal View

Why is economical marine renewable energy taking so long?
D Ayling

Technical Papers

High–frequency multibeam echo–sounder measurements of seafloor backscatter in shallow water: Part 1 – Data acquisition and processing

IM Parnum and AN Gavrilov

Abstract: Methods for processing multibeam echo–sounder (MBES) bathymetry data are well established, however, there is no universal and established approach to processing and interpretation of MBES backscatter data. The aim of this paper is to (1) detail the different backscatter logging methods implemented in modern high–frequency MBES systems used primarily in shallow water; (2) describe and suggest appropriate methods of data processing; and (3) discuss likely errors and artefacts expected from MBES backscatter processing. These issues are illustrated using data collected with a Reson SeaBat MBES in coastal shelf areas of Australia, although the methods and errors discussed are relevant to other high–frequency shallow–water MBES systems. Production of backscatter mosaics and analysis of backscatter for seafloor classification using MBES data are considered in Part 2 – Mosaic production, analysis and classification (Parnum and Gavrilov, 2011), published alongside this paper.

 

High–frequency multibeam echo–sounder measurements of seafloor backscatter in shallow water: Part 2 – Mosaic production, analysis and classification

IM Parnum and AN Gavrilov

Abstract: Backscatter measurements collected with high frequency multibeam echo–sounders (MBES) have been used to map the spatial distribution of seafloor types and properties in shallow waters. The methods for collection and processing of MBES backscatter data were considered in Part 1 – Data acquisition and processing (Parnum and Gavrilov, 2011), published alongside this paper. The aim of Part 2 is to describe the main methods used to produce backscatter maps of the sea floor free from angular artefacts, and to classify seafloor types based on backscatter and bathymetry analysis. These methods are illustrated using a dataset collected with a Reson SeaBat 8125 MBES in Esperance Bay in Western Australia, although the methods and errors discussed are relevant to other high–frequency shallow–water MBES.

 

The Danish wind industry 1980–2010: Lessons for the British marine energy industry

K Smith

Abstract: The following paper presents the differences in the development of the Danish and UK wind industry in order to highlight key issues that led to their respective success and failure. By comparing the political, economic, social and technological policies that have defined the growth of the two industries, the paper contends that the lack of a clear and consistent market price support mechanism together with a slow planning process and delayed grid access were significant weaknesses in the UK. It also suggests that these factors must be addressed to ensure the same barriers do not stunt the growth of the UK marine renewable industry. To maintain the lead in an emerging marine energy industry, the UK government must facilitate strong public support for wave and tidal energy in parallel with assisting with R&D and project capital grants. Clear and consistent policy with regard to price support mechanisms and priority access to the grid are necessary to ensure a stable and reliable market. Lessons learned from the success of the Danish wind industry must be applied if the UK wishes to secure a stronghold in this market.

Technical Briefings

Integrating reliability, obsolescence and integrity management into life cycle management of subsea facilities

JHA Baker
Abstract: This paper recommends that the reliability, obsolescence and integrity management processes related to subsea fields should be integrated into a single process, here termed ‘life cycle management’, because they all treat in a similar way with the same systems, the overall aim being to maintain system integrity and availability throughout field life. This paper asserts that all three processes should commence early in the design phase of a project and be carried through to decommissioning. It also discusses failure modes, effects and criticality analysis (FMECA) which, it is proposed, should be developed into an integrated system in support of life cycle management, reflecting the root causes of failure as a means of identifying effective and measurable mitigation activities.

 

Maritime shipments of highly radioactive material between Europe and Japan

G Plant

Abstract: This article examines, in the wake of the Fukushima incident, the adequacy of operational safeguards and national and international control measures and oversight established to mitigate the health and safety and environmental risks posed by the ultra–hazardous shipments of highly radioactive materials between Europe and Japan. It describes the technical measures taken to ensure safety, primarily through package design and secondarily by way of ship design and ship–based measures. It then critically examines the international regulatory requirements and guidance for package design and ship–based measures, including those governing loss, monitoring and possible recovery of cargoes in the deep waters normally frequented, or elsewhere at sea. Finally it considers the pressures from many concerned en route states (and non–governmental organisations (NGOs)) for further regulation, notably in the form of routing restrictions, prior authorisation or informed consent regimes or notification regimes.

Book Reviews

Project Azorian: The CIA and the Raising of the K–129 by Norman Polmar and Michael White

Reviewed by S Hall

 

Understanding Earth’s Polar Challenges: International Polar Year 2007–2008, summary by the IPY Joint Committee

Summary by C Summerhayes

Underwater Technology Vol 30 No 2

Oceanology International Special Issue

Autumn 2011

A Personal View

Conferences – time for a new approach?

G Griffiths

Technical Papers

Coral resilience on the reefs of Jamaica

MJC Crabbe

Abstract: Awareness of important factors for coral reef growth helps reveal how reef ecosystems react following major anthropogenic and environmental disturbances. Physical measurements by SCUBA divers, together with an underwater remotely operated vehicle (ROV), have been used to study environmental and climate effects on corals on fringing reefs in Jamaica. The period of this study, from 2002 to 2008, covers the major Caribbean-wide bleaching event of 2005. For 624 non-branching corals at Rio Bueno and Dairy Bull reef near Discovery Bay on the north coast of Jamaica, skewness values for coral populations at the two sites showed generally positive values, indicating that small colonies predominated over large colonies. Measurement of coral sizes together with growth rates allowed the estimation of recruitment dates. This was done for 235 non-branching corals near Kingston Harbour, on the south coast of Jamaica. The aim of this study was to use coral size and population dynamics as a metric for coral resilience, and to assist marine park managers of coral reefs with regard to coral recruitment and growth. The data show that while recruitment of small corals was returning after the major bleaching event of 2005, larger corals were not necessarily resilient. Therefore there is a need for careful management if the reefs are to survive such major extreme events.

 

EMECO Datatool: A regional scale data integration and assessment system for marine environmental policy needs

DK Mills, K Keeble, J Foden, RM Forster, J Rees, S Keeble, SJ Malcolm

Abstract: As part of the European Marine Ecosystem Observatory (EMECO) initiative, the web-based EMECO Datatool has been developed, enabling rapid integration and visualisation of multi-platform, multi-parameter and multinational data at a regional scale. It delivers transparent, auditable, cost-effective, policy-relevant information, e.g. suitable for assessing good environmental status for the EU Marine Strategy Framework Directive. Currently, there are 14 biological, chemical and physical parameters sourced from traditional and novel observing platforms, which users can query and view as integrated datasets, time-series plots and bespoke assessment maps. Following successful completion of its original purpose (an integrated map of chlorophyll for the North Sea), the range of data sources and the spatial domain are currently being extended within the tool.

Technical Briefings

Development of a new unmanned semi-submersible for the efficient deployment of sensors at sea

D Hook, R Daltry, P Alleman, J Cheramie, C Wolking and A Kleiner

Abstract: This paper describes the work undertaken during the design, construction and test phases of a radical new format of unmanned surface vehicle. This semi-submersible design offers seakeeping characteristics that reduce the weather downtime during hydrographic surveys and significantly improve data quality. The vehicle detailed within this paper has both commercial and military applications in efficiently deploying sensors at sea.

 

Caspian pin pile wizards: Innovative positioning technology supports jacket installation stability

W Jardine and D Fallance

Abstract: This paper describes as-built position methodology and execution processes that delivered better than ±50mm relative positioning of pin piles over 90m baselines, in 175m water depth. The piles were installed to allow immediate stabilisation of 15 800 tonne jackets docked onto the piles. Updated processes for a future installation are visited to see how lessons learned on the project can be integrated into a future project.

 

The operational evaluation of an inertial navigation technique for the provision
of underwater metrology surveys

F Auger and K Vickery

Abstract: Total Exploration and Production Congo placed an operational survey contract in 2008 for the detailed evaluation of the use of inertial navigation systems (INS) for the provision of subsea metrology surveys. The inertial system was used offshore in parallel with conventional acoustic positioning systems commonly used for metrology surveys. This paper presents multiple datasets from this work, as well as operational timing discussions reviewing the efficiency of these operations, and compares inertial techniques with conventional methods. The paper concludes that inertial systems can provide the required survey accuracy while consuming significantly less operational time and resources than conventional techniques. This paper discusses the last three years of field operations and compares the results and operational benefits of the conventional and inertial techniques.

Book Review

Deep Water – The Gulf Oil Disaster and the Future of Offshore Drilling, published by National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling

Reviewed by C Summerhayes

Book Review

Troubled Waters: Ocean Science and Governance, edited by Geoff Holland and David Pugh

Reviewed by T Guymer

Underwater Technology Vol 30 No 3

Spring 2012

A Personal View

Specifying underwater man-made noise – the need for a sound approach

S Robinson

Technical Papers

Technology requirements to investigate the effects of sound on marine wildlife

IL Boyd

Abstract: There is little information about the effects of sound on marine life. In spite of this high uncertainty, several new legal limits to sound levels in the marine environment are being introduced. The present paper summarises the conclusions drawn at a workshop that took a prospective view of the technological developments necessary in order to make significant progress with reducing these uncertainties. These developments would mainly aim to further the understanding of how sound may affect some of the most vulnerable marine species. The most important methods available to examine the effects of sound will involve the development of instruments that measure the received levels of sound at the animal and its behavioural response. The availability of power to operate instruments used in remote sensing is the main factor that limits most aspects of technology capability. Alternatives need to be developed to using sparse data (from a few instruments that are attached to animals or that are widely spaced), and a coordinated approach is required between commercial suppliers and academics to overcome the current constraints, foster innovation and turn new approaches into operational tools. There is also a need to improve the technology used to attach instruments to animals, particularly in the case of small cetaceans. Improved bandwidth for data communication, recovery or retrieval is likely to develop alongside other innovations as a result of improvements in large-scale infrastructure such as satellite systems. There is scope for innovation of sensors to improve the ability to measure behavioural/physiological response variables such as heart and/or respiration rate.

 

Capturing convection in the northwest Mediterranean Sea: using underwater gliders to assess the performance of regional forecast models

BR Loveday, S Swart and D Storkey

Abstract: Ocean models require independent datasets to verify forecast accuracy. Glider data, within an appropriate reference frame, can satisfy this constraint. In the present paper, profiles from the northwest Mediterranean Sea are re-gridded to allow evaluation of modelled deepwater formation episodes. Time-series analysis of temperature, salinity, mixed-layer depth and ocean heat content show that the simulated response to surface flux is consistent with observations and the evolution of convective events is well represented. However, discrepancies in the distributions of the simulated Levantine Intermediate Water (LIW) and western Mediterranean deep water (WMDW) remain. A new ‘sweep’ methodology, developed in the present paper, indicates that the location and duration of the simulated convective events are consistent with that observed, but spatial variability is underrepresented. Variogram analysis ascribes integral scales similar to those observed for the mixed-layer depth, but suggests that simulated scalar fields are too diffuse. The ability to maximise the separation of temporal and spatial variability, inherent in this new methodology, confirms that glider data is suitable for validating high-resolution ocean models.

 

Subsea technologies selection using analytic hierarchy process

S Yasseri

Abstract: One of the primary issues in the offshore oil and gas development is the comparative evaluation of subsea production versus other alternative means. Another issue of importance is assessing the technologies to be used for each concept. The present paper concentrates on such assessments and aims to develop a method for selecting the most appropriate technologies or components for the subsea production systems. Financial viability is the main driver of the concept selection, but the most important decision variables for selection are: technology readiness, reliability and availability, constructability, maintainability, operability and costs. Technology selection requires the combination of these decision variables, as they impact both cost and benefit. The paper provides an integrated analytic framework, using the analytic hierarchy process (AHP) for technology selection that best satisfies all of a decision-maker’s requirements. A survey of all decision influencing factors is presented in the present paper, as well as a case study, a sub-set of which is used to demonstrate the selection process between two subsea trees manufactured by different suppliers. The emphasis is on the practicality and accessibility of AHP.

Technical Briefing

Subsea processing – a holistic approach to marginal field developments

N Abili, O Udofot and F Kara

Abstract: The application of full subsea processing to develop remotely located marginal fields offshore West Africa is an attractive option for breaking the techno-economic barriers which have long hindered the development of these fields. Some of the fields have remained marginal and unproduced over the years, arguably owing to incorrect estimates in recoveries and economics occasioned by erroneous estimates in basic input parameters. Therefore, the right method of application for developing marginal fields must be sought to ensure that both national and international operating companies partake in the development of these fields. The present paper explores the use of full subsea processing (FSP) technology to develop marginal fields economically.

Book Review

Arctic Security in an Age of Climate Change, edited by James Kraska

Reviewed by T Potts

Book Review

The Dance of Sea and Air: How oceans, weather and life link together, by Arnold H Taylor

Reviewed by R Rayner

Underwater Technology Vol 30 No 4

International Symposium of Occupational Scientific Diving Special Issue

Summer 2012

A Personal View

Scientific diving: towards European harmonisation

M Ponti

Technical Papers

Surveying black bream, Spondyliosoma cantharus (L.), nesting sites using sidescan sonar

KJ Collins and JJ Mallinson

Abstract: Black bream, Spondyliosoma cantharus (L.), are summer visitors to the south and west coasts of the UK, overwintering in deeper waters and migrating inshore to breed from April to June. Bream are demersal spawners, with the eggs laid in a nest excavated by the male as it creates a depression in a sandy gravel substrate. To build their nests, male bream expose bedrock and gravel by using their tails to remove the surface layer.
The present study, using sidescan sonar and SCUBA diving, extends the known occurrence of extensive nesting grounds off the West Sussex coast to the Isle of Wight and Dorset. The nests are typically circular craters 1–2m wide, and 5–30cm in depth, which can clearly be seen using sidescan sonar as groups of circular depressions. Several thousands of eggs (1–2mm) are attached to bare rock in the centre of these structures. All the eggs hatch by July.
The species is valuable and particularly vulnerable to exploitation by both sport and commercial fishermen during its nesting season. With no minimum landing size and no prescription for Total Allowable Catch or the International Council for the Exploration of the Sea (ICES) stock assessment, they are suitable for protection under spatial planning measures, such as through the use of marine protected areas (MPAs).

 

GPS diving computer for underwater tracking and mapping

B Kuch, G Buttazzo, E Azzopardi, M Sayer and A Sieber

Abstract: Obtaining accurate and affordable geo-referencing is not straightforward for divers because there is a lack of through-water penetration by global positioning systems (GPS). Although a number of commercially available systems exist, few are low-cost or operationally flexible enough for use in scientific diving. The present paper details a new GPS diving computer that supports navigation and Global System for Mobile Communications (GSM) underwater. The unit displays the distance and heading information to set points and tracks the dive in three dimensions (position, depth and time). When downloaded, the tracked dive profile can be visualised in 3D in Google Earth. By synchronising the dive computer clock to external recording devices (for example, cameras), any recording event can be geo-referenced with attached data relating to GPS position, temperature and depth.

 

Development of a head-up displayed diving computer capability for full face masks

A Sieber, B Kuch, P Enoksson and M Stoyanova-Sieber

Abstract: Professional divers often dive in conditions of very low visibility. In such situations, a head-up display has many advantages as water clarity does not affect the ability to see the display. In addition, a head-up display allows divers to continuously monitor all relevant dive data without interrupting their work. The present paper details the development of a new diving computer that has been designed with a head-up display and integrated into an AGA type full face mask. The device includes a full colour display, depth sensor, tilt-compensated compass and a tank pressure sensor. Typical dive relevant data (depth, time, decompression obligations) including tank pressure and heading are displayed and stored in the internal flash memory.

 

Monitoring the effectiveness of re-establishing beaches artificially: methodological and practical insights into the use of video transects and SCUBA-operated coring devices

M Vacchi, A Rovere, CF Schiaffino and M Ferrari

Abstract: Artificially rebuilding beaches is one of the main methods used to stabilise or restore them after severe erosion events. Best practices should involve some form of monitoring prior to, during and post beach re-building. The most frequently applied monitoring techniques for Italian (and Mediterranean) beaches are topographic and bathymetric surveys carried out in regular time intervals in order to understand beach evolution. Morphological studies, based on grain-size profile analyses, can indicate the sedimentary evolution of the beach.
In the present study, SCUBA diving techniques were employed in addition to traditional survey methods in order to monitor two study areas along the Ligurian coast (northwest Mediterranean Sea): Ospedaletti and Genova Vernazzola. In particular, a diver-operated, cost-effective coring system obtained marine sediment cores, and video transects and inspections generated information on the status of coastal defence structures (e.g. groynes). Using those methods, the main vertical discontinuities along the submarine beach were identified, as were points of erosion on the submarine parts of groynes. Such innovative techniques provided data that are not easily achievable with traditional monitoring techniques. Future monitoring programmes should consider these new methods as a way of improving assessment efficiency.

 

Ancient coastal landscape of the marine protected area of Porto Cesareo (Lecce, Italy): recent research

C Pizzinato and C Beltrame

Abstract: In 2008 and 2009 the Archeotema society (Venice, Italy) was contracted by the Libyan government to outline a project for the management of the underwater archaeological sites of Libya as places for underwater tourism. The project was part of a general remit of Evaluation and Conservation of the Cultural Libyan Heritage.
A selected site was Apollonia in Cyrenaica. The ancient harbour with all its structures allowed for the visualisation of a real park with an itinerary for divers and a glass-bottom boat for people to see from the surface.

Technical Briefing

A project for the creation of an underwater archaeological park at Apollonia, Libya

C Pizzinato and C Beltrame

Abstract: In 2008 and 2009 the Archeotema society (Venice, Italy) was contracted by the Libyan government to outline a project for the management of the underwater archaeological sites of Libya as places for underwater tourism. The project was part of a general remit of Evaluation and Conservation of the Cultural Libyan Heritage.
A selected site was Apollonia in Cyrenaica. The ancient harbour with all its structures allowed for the visualisation of a real park with an itinerary for divers and a glass-bottom boat for people to see from the surface.

Book Review

Scientific Diving Techniques: A practical guide for the research diver, by John Heine

Reviewed by G Caramanna

Underwater Technology Vol 29 No 1

Spring 2010

A Personal View

Under–ice technologies for detecting climate change

C Summerhayes

Technical Papers

The natural oceanic carbon and sulfur cycles: implications for SO₂  and CO₂ emissions from marine shipping

P Williams

Abstract: The principal objectives of this paper are: first, to provide a background to the natural cycles of carbon and sulfur in the oceans, along with essential reference data; second, to outline the behaviour of the seawater carbonate buffer system and how it responds to additions of the combustion gases carbon and sulfur dioxides. The report then explores the respinse of the seawater system to these gases, as produced by combustion of marine fuel oil, and illustrates the impact of these gases in comparison with their natural cycles and other anthropogenic inputs. Finally, the consequences on the ocean chemistry of removing sulfur from fuel oil during refining, or leaving the fuel untreated, are explored. Essential points coming out of this research are:

• The scale of the oceanic C–cycle is in the region of 500–15000×10¹²moles C/annum. This compares with a total anthropogenic CO₂ production of 500×10¹²moles C/annum. and shipping fuel oil release of 25×10¹²moles C/annum

• The oceanic S–cycle is of the order 4×10¹²moles S/annum; S–emissions from shipping fuel are estimatred as 0.25×10¹²moles S/annum. The collective anthropogenic emissions amount to 2.6×10¹²moles S/annum

• The chemical reactions and equilibria associated with the release of the two gases CO₂ and SO₂ will be completed long before the receiving water sinks and loses contact with the atmosphere. This they can be treated as being in equilibrium with the atmosphere

• Absorption of the S–combustion products by the oceans will give rise to emissions of CO₂ in a C:S molar ratio of 1.7

• Of the two combustion gases CO₂ and SO₂, the former has the greatest immediate effect on ocean chemistry in the case of pH, allowing for a S:C ratio of 1.84 – 80–fold greater (expressed as pH units)

• This dominance is lost when the impacted water comes in contact with the atmosphere. The asses CO₂ is lost from the water sample, so the pH effect due to CO₂ is also lost. The pH effect due to SO₂ persists, but is reduced some 11–fold by loss of CO₂ to the atmosphere

• Purification of the fuel oil, by reducing its sulfur content, reduces the emission of CO₂ into the atmosphere due to SO₂ . However, the desulfurisation process requires energy, and the CO₂ released in order to provide this essentially the same as the reduction of CO₂ emission due to the reduced SO₂ release on combustion

• The circumstances surrounding the effect on the pH of seawater upon removing the sulfur, or leaving the oil untreated, are more difficult to resolve due to problems over different time frames.

From the perspective of the impact on the chemistry of the oceans, it would appear to matter little whether sulfur is removed from marine fuel oil or not, as the effect on ocean pH and the emission of CO₂ into the atmosphere ends up as much the same. The acidification of the oceans due to the sulfur in marine fuels is minute: three orders of magnitude less (in pH unites) that are due to the CO₂ accumulation in the atmosphere from the combustion of fossil fuels.

 

Review of diver noise exposure

TG Anthony, NA Wright and MA Evans

Abstract: Divers are exposed to high noise levels from a variety if sources both above and below water. The noise exposure should comply with ‘The Control of Noise at Work Regulations 2005’ (coNaWR05, 2005). A detailed review of diver noise exposure is presented, encompassing diver hearing, noise sources, exposure levels and control measures. Divers are routinely exposed to a range of noise sources of sufficiently high intensity to cause auditory damage, and audiometric studies indicate that diver hearing is impaired by exposure to factors associated with diving. Human hearing under water, in cases where the diver’s ear is wet, is less sensitive than in air and should be assessed using an underwater weighting scale. Manufacturers of diving equipment and employers of divers have a joint responsibility to ensure compliance with the exposure values in the CoNaWR05, although noise is only one hazard to a diver, and a balanced risk assessment must be applied to the whole diving operation. A diver noise reduction strategy is proposed, and a health surveillance programme involving audiometric tests for divers should be established.

 

The influence of block shape, water depth and analysis technique on the measured profiles of artificial reefs

MDJ Sayer and CJ Brown

Abstract: Artificial reefs are constructed for many reasons around the world, but they usually have to comply with some form of regulation which may require demonstration of accurate deployment through some form of post–construction measurement. Reefs related to fisheries are often subjected to scientific census to assess whether production and/or residence is related to reef size and cost. Once deployed under water, there is the obvious problem of obtaining an accurate assessment of the size and shape of reefs. This study examined two methods for estimating reef size that were employed on a large–scale matrix for 30 separate artificial reefs constructed off the west coast of Scotland: (1) measurements made by standard SCUBA divers and (2) estimates based on raster graphic image analysis of images created from multibeam echosounder (MBES)xyzdatasets. The degree of agreement ranged between the two methodoloies with no obvious trends; it was assumed that the MBES data would be more accurate because of the lower numbers of assumptions. More simple–shaped blocks produced more shallow and scattered profiles than the blocks containing voids. More reef scatter (as measured by footprint area recorded at greater water depths.

Technical Briefing

Trials of Crowcon H₂ S Gasman for use in an operational diving bell

V Flook

Meeting Report

Selected Summary Highlights from the 31st Consultative Meeting (LC31) of Contracting Parities to the Convention on the Prevention of Martine Pollution by Dumping of Wastes and Other Matter 1972 (London Convention 1972) and the 4th Meeting of Contracting Parties to the 1996 London Protocol (LP4) to the London Convention (London Protocol), 26–30 October 2009 in London, at the International Maritime Organization (IMO)

P Verlaan

Book Review

Ecological Indicators for Coastal and Estuarine Environmental Assessment: A User Guideby JC Marques, F Salas, J Patricio, H Teixeira and JM Neto

Reviewed by DA Purdie

Underwater Technology Vol 29 No 2

Summer 2010

A Personal View

Validating scuba as research methodology
M Lang

Technical Papers

A review of the technical specifications of 47 models of diving decompression computer

E Azzopardi and MDJ Sayer

Abstract: Many modern diving decompression computers have the ability to record and display information of, and related to, the dive profile. In the UK, there are currently approximately 50 models of diving decompression computer being sold with a capability for recording and downloading dive information. Based on the technical information either supplied with each computer or made available on the internet this present study presents examples of 47 of these downloadable computers to review some of the parameters that are commonly measured, recorded and/or displayed such as: depth recording and/or measurement frequency, and/or measurement resolution, method of recording/display (e.g. maxima, minima, average, thresholds), methods of downloading information, and what data are stored and storage limitations. Although there is a wide range in the technical capabilities of the computers reviewed they all record and store similar basic dive profile information. However, the present review highlights the variation in many of the recording/measuring formats and download methodologies.

A review of the use of closed–circuit rebreathers for scientific diving

A Sieber and R Pyle

Abstract: Rebreather diving systems have many advantages to standard open–circuit systems (or SCUBA). Re–breathers offer higher gas efficiency together with silent and bubble–free diving. Moreover, instead of cold and dry gas found in open–circuit systems the diver takes advantage of a warm and humid breathing gas. Stealth (through silent, bubble–free diving) can be beneficial for scientists exploring a range of natural ecological research areas. The high gas efficiency of rebreathers, combined with their lower operational costs, can provide longer autonomy and shortened decompression obligations that may assist the scientist with deeper diving explorations. The present paper gives an overview of today’s rebreather technology and focuses especially on the needs of scientific divers. Moreover, it includes a short report about achievements in the field of deep coral explorations, where advanced electronically–controlled closed–loop rebreather systems were the key for efficient and successful missions.

Study of the environmental effects of submarine CO₂–rich emissions by means of scientific diving techniques (Panarea Island – Italy)

G Caramanna, S Espa and V Bouché

Abstract: To study the effects of anomalous concentrations of CO₂ in the sea a volcanic area was identified in the southern Tyrrhenian Sea, where submarine CO₂–rich discharges occur in shallow water producing under–water gas plumes. Specific fluid sampling and water–chemistry measuring techniques were developed to be used by scientific divers in order to identify the chemical composition of the gas emissions and their effect on the marine surroundings. Laboratory experiments were conducted to identify the main features of the physical interaction of a gas plume with the surrounding liquid environment.

Technical Briefings

Italian underwater exploration in Antarctica: scientific diving and ROV operations

R Palozzi, M Vacchi, R Bono, F Catalano and A Rovere
Abstract: Italy established its first base in Antarctica in 1986 at Terra Nova Bay (Ross Sea) and since 1987 underwater activities have been undertaken, both in ice–free waters and under the ice, mainly in support of scientific research. Scuba diving and robotic underwater explorations were undertaken following the regulations and the guidelines settled by Programma Nazionale Ricerche in Antartide (PNRA). This present account gives a brief history of the most important underwater activities led by the Italian Programme highlighting studies of macro benthic assemblages as well as the work needed to collect information on biology, geology, glaciology, geodesy, geophysics, oceanography. A brief overview of the PNRA diving guidelines is given.

Geomorphologic survey and hydrological measures of a karst spring by means of cave diving techniques (Amaseno, Italy)

G Caramanna and M Giordani

Abstract: Scientific cave diving techniques were employed to explore and study the cave “Capo d’Acqua d’Amaseno”, which is located in the southern Latium Region (Central Italy) about 80km southeast of Rome. The cave is fed by a karst system and its dimensions permit exploration through use of diving. Inside the cave a small underground lake was discovered and its level was monitored by deploying a water–level data–logger and comparing it with the rainfall measured in the area. First results highlight the fast response of the lake level to the rainfall; this is in agreement with the characteristics of a system fed by large karst conduits.

Book Review

Another Whitstable Trade: An Illustrated History of Helmet Divingby John Bevan

Reviewed by TG Anthony

Underwater Technology Vol 29 No 3

Autumn 2010

A Personal View

The scientific diving challenge in Europe
J–P Féral

Technical Papers

Preliminary characterisation of a shallow water hydrothermal sulphide deposit recovered by scientific divers (Aeolian Islands, southern Tyrrhenian Sea)
AM Conte and G Caramanna
Abstract: Active hydrothermal vents, mainly occurring along the mid–ocean ridges, are also found in shallow–water environments in volcanic areas. This paper presents data for a shallow–water vent and associated sulphide hydrothermal deposits located east of the volcanic island of Panarea (Aeolian Archipelago, southern Tyrrhenian Sea). The vent lies at a depth of 25m on the seafloor in an exhalative area characterised by the presence of several vents (Caramanna et al., 2003, 2005; Anzidei et al., 2005; Esposito et al., 2006). Samples of the hydrothermal deposits were collected by scientific divers in January 2007. The ore mineralogy components of the deposits, mostly Pb–As sulfosalt, Zn–Pb sulphide and barium sulphates, reveal a genetic analogy with late–stage, low–temperature products of Kuroko–type mineralisations in subduction–related tectonic settings.

The impacts of anchoring and mooring in seagrass, Studland Bay, Dorset, UK

KJ Collins, AM Suonpää and JJ Mallinson

Abstract: Studland Bay, Dorset, on the central south coast of England is shallow and well protected from the prevailing south–west winds, making it an ideal habitat for a dense seagrass bed of Zostera marina. The shelter and proximity to the port of Poole make it a popular anchorage. Bare patches in the seagrass habitat associated with boat anchoring and mooring are described. Shear vane stress of the seabed was measured in situ by SCUBA divers. When comparing the undisturbed seagrass sediment with the bare, impacted areas, the latter sediments are less cohesive, contain less organic material and have a lower silt fraction, infaunal organism number and taxa. A mechanism for the progression of an anchor scar is suggested, involving storm wave induced mobilisation and dispersion of the impacted sediments exposing the underlying rhizome mat, which is further undermined by crabs. Results from this work and studies on other seagrass species suggest that the recovery is far from straightforward. It may take many years, leading to the decline of the Studland Bay seagrass habitat and associated species.

 

The underwater exploration of the Merro sinkhole and the associated diving physiological and psychological effects.

R Palozzi, G Caramanna, P Albertano, R Congestri, L Bruno, R Romano, MG Giganti, R Zenobi, C Costanzo, G Valente, D Polani, M Vecchio, M Vinci and V Sbordoni

Abstract: The Pozzo del Merro (Merro sinkhole), a few kilometres away from Rome, Italy, is the deepest flooded karstic cavity known in the world. Over the last two years, a multi–disciplinary scientific research project studied the almost unknown aquatic ecosystem of the sinkhole while also studying the psychological and physiological reactions of scientific divers operating in the very hostile underwater environment. This paper presents a preliminary overview of the seven studies carried out in parallel and attempts to highlight the fundamental role of scientific diving in contributing to increased knowledge about this extreme environment. The discovery of two exotic species in the sinkhole represents a paradigmatic case of the problem of invasive species introduction in such a unique environment. The project also included research on human diving physiology, pathology and psychology through monitoring of all the divers (plus one free–diver) working in the Merro sinkhole.

 

Early development of the subtidal marine biofouling on a concrete offshore windmill foundation on the Thornton Bank (southern North Sea): first monitoring results

F Kerckhof, B Rumes, T Jacques, S Degraer and A Norro

Abstract: In 2008 the building of a first windmill park some 30km off the Belgian North Sea coast began. Such offshore constructions represent a novel, artificial, hard substratum habitat on the Belgian continental shelf, where the sea–bottom consists mainly of sandy and muddy sediment. It is anticipated that in the coming years, several hundreds of offshore windmills will be constructed in a dedicated zone off the Belgian coast. SCUBA–based in situ techniques were used to document and sample the fouling assemblage on the hard substratum represented by the concrete foundations of the first windmills constructed in Belgian waters. Here this paper presents and discusses the results of the monitoring undertaken from February 2009 to February 2010. Despite the further offshore location and differences in substratum type, the preliminary results indicated that the overall structure of the marine biofouling assemblage at the Thornton Bank site is similar to that on the foundations of other offshore wind farms in Germany, Denmark and the Netherlands, as well as on other hard structures in the North Sea.

Technical Briefing

ROV–SCUBA integrated survey of the Montecristo Island Nature Reserve (Tuscan Archipelago National Park, Mediterranean Sea)

L Angeletti, A Ceregato, M Ghirelli, B Gualandi, E Lipparini, D Malatesta, A Sperotti and M Taviani

Abstract: A remotely operated vehicle (ROV) survey aimed at exploring the waters around Montecristo Island, a nature reserve in the Tuscan Archipelago (Tyrrhenian Sea), was carried out in summer 2008 down to a maximum depth of ca. 160m. The main target of this exploration was checking the potential occurrence of deepwater scleractinian corals. Whilst the ROV transects did not document any deepwater corals, they did reveal that the coarse detrital bottom of the Montecristo granitic edifice between 110–160m was dominated by a crinoid facies made of Leptometra phalangium (Müller, 1841) with a density of up to 15 individuals per m².

Book Review

The First Treasure Divers: The True Story of How Two Brothers Invented the Diving Helmet and Sought Sunken Treasure and Fame by John Bevan

Reviewed by G Momber

Underwater Technology Vol 29 No 4

Spring 2011

A Personal View

Marine science and engineering challenges – the need for a marine technology strategy

C Summerhayes

Technical Papers

The design strategy and methodology of the RAPID–MOC project moorings

D Rayner and T Kanzow

The use of scientific moorings is a long established method for obtaining timeseries data from the ocean, and they are often deployed for long periods at a time – sometimes for many years. As many moored instruments log data internally and are unable to transfer them to shore, moorings must be recovered for the data to be downloaded. Scientists therefore rely on not only the mooring collecting data as planned, but also the hardware surviving the deployment period. It is important to be able to predict mooring behaviour when subjected to environmental conditions at the site to ensure that they will be able to perform the required scientific tasks, such as collecting measurements at the correct depths. This paper presents the design strategy used by the Natural Environment Research Council’s Rapid Climate Change Meridional Overturning Circulation (RAPID MOC) project. It discusses how the designs have evolved during subsequent deployments to improve the quality of the data collected and to reduce the risk of instrument and data loss impacting on the scientific objectives of the project.

 

Combining underwater visual census and self–organising maps: a freshwater ecology application

R Palozzi, M Quartararo, M Marcelli, FM Arati and P Boccanera
Abstract: A very small and deep lake (a sinkhole) in Central Italy was studied during summer 2010 adopting an artificial intelligence based method, the self–organising map (SOM), for the analysis of data collected by a slightly modified underwater visual census (UVC) technique (strip–transects). The data were collected on the assemblage structure and individual age/size of the summer fish found in the sinkhole. UVC data are known to be in some cases partially unreliable for common quantitative statistical analysis (being noisy, uncertain and redundant, particularly in small systems). A specific type of artificial neural network (the SOM) was therefore put forward as a suitable solution for properly extracting information from this kind of data. In the past two decades SOMs have proved to be often more appropriate than other common multivariate techniques in assessing a range of ecological issues. Nevertheless, no study has explicitly taken advantage of the potential of using SOMs with UVC data. The paper gives a brief example of how SOMs can be used to represent and analyse multivariate patterns of a fish assemblage.

 

Design and testing of an acoustic ranging technique applicable for an underwater positioning system

E Gamroth, J Kennedy and C Bradley

Abstract: The design and preliminary testing of a prototype ranging system, capable of being utilised by an underwater positioning system, is presented in this paper. The system extends the reach of the terrestrial global positioning system (GPS) to the subsea environment. The prototype system incorporates a topside surface buoy that receives and relays the GPS data, via acoustic signals, to the subsurface receiver. The receiver calculates the range from the topside buoy using the coded acoustic signal. Key operating characteristics of the system are experimentally investigated: long– and short–range accuracy, repeatability and resolution. The prototype ranging system also demonstrates the feasibility of a full–up underwater vehicle positioning system (comprising three topside buoys and a receiver). The ranging system’s experimental performance has been extrapolated to show that a theoretical position accuracy of 6.5m will be attainable for an unlimited number of underwater receivers operating within a 1km² workspace.

 

Bubble model based decompression algorithm optimised for implementation on a low power microcontroller

B Kuch, B Buttazzo B and A Sieber
Abstract: The calculation of a decompression schedule, according to the Varying Permeability Model (VPM) with Boyle’s Law compensation extension, requires many sophisticated arithmetic operations. Therefore if it is calculated with a limited arithmetic instruction set on a microcontroller, a decompression schedule cannot be calculated in an acceptable time frame. This paper describes the principles behind an optimisation in calculation speed of the VPM with the Boyle’s Law compensation extension for the determination of decompression schedules on a low power microcontroller. It was accomplished in three independent steps: converging the cubic root equation of the Boyle’s Law compensation algorithm; using a set of predictive models to calculate the adapted bubble radius without using a cubic root solver; and pre–calculating the exponential terms of the Haldane and Schreiner equations, in order to reduce processing time and dynamic adjustment of the step size within the iterative process of the decompression schedule calculation. The modified algorithm was tested on an Atmel ATmega644P running at 8MHz. Calculating decompression schedules with these enhancements were approximately five times faster than with the original algorithm.

Technical Briefings

Development of a graphical head–up display (HUD) for rebreather diving

B Koss and A Sieber

Abstract: Head–up displays (HUDs) are mounted in the field–of–view in close proximity to the eye. The present work describes the development of HUDs for rebreather diving. The developed HUDs feature a micro–screen instead of LED–based systems found in nearly all existing available commercial units. Two mouthpiece– mounted prototypes were developed. However, this approach turned out to be impractical and a better solution was found with mounting the HUD directly onto the diver’s mask. A split optical path, where the HUD is glued to the visor, and a small lens located inside the diving mask were key features enabling a compact and lightweight design while, at the same time, withstanding pressure and water ingress.

 

The Environment Council and marine renewable energy

R Parrott and J Griffiths

Book Review

Of Seas and Ships and Scientists edited by Anthony Laughton, John Gould, ‘Tom’ Tucker and Howard Roe

Reviewed by G Griffiths

Underwater Technology Vol 28 No 1

Winter 2008

A Personal View

The role of subsea in the UK

B Jones

Technical Papers

Moisture levels in compressed breathing air

TG Anthony and PR Clarke

Abstract: The purity and quality of compressed breathing gases are specified to cover both their physiological and engineering safety aspects. The permissible water content specified in British Standards Institution BS EN 12021 (BSI, 1999) for compressed air at pressures less than 40 bar are confusing. This paper proposes guidance for the diving industry on maximum permissible water content for compressed air at pressures less than 40 bar. The relationship, based on the Magnus equation, of the pressure within a compressed air system, the ambient temperature, the water content (i.e. volumetric humidity) and the pressure dew point (i.e. temperature at which liquid water or ice will form) was used to identify operational guidelines. Two tabular format operational guidelines, one simple and the other flexible, have been developed for the water content of compressed air at pressures less than 40 bar. The ‘simple’ tabular system has been proposed as the preferred system.

 

Antenna design for the propagation of EM waves in seawater

CK Yip, A Goudevenos and J Lucas

Abstract: A new design for a transmitting antenna suitable for generating subsea EM waves for the frequency range 1–100MHz is given in this paper. It operates by electrically exciting water molecules to emit dipole radiation. The new design of antenna uses a parallel wire transmission line immersed in pure water contained within a PVC barrel, in order to efficiently generate the dipole oscillations. This mode of dipole radiation generation has an optimum signal output when the dipole dielectric conductivity is compared with the water conductivity. When using distilled water having a conductivity of 2×10–4S/m, this occurs for frequencies above 20MHz.which is suitable for subsea video signal propagation at 25 frames per second. The barrel antenna produces up to a 40dB increase in emitted signal when compared with a coated double–loop antenna placed directly in the seawater. However, a conventional coated, double–loop antenna in seawater is suitable to be the receiving antenna. The reason is because the double–loop antenna, w2hen operating as a transmitter, has to initially generate on electric field within the seawater., which then excites the water molecules. The receiver can directly pick up the propagated EM wave. A less efficient design of the new antenna, which is however more compact, has been achieved by placing the parallel–wire transmission–line dipole transmitter within a water–filled cylindrical PVC tube. For short–distance propagation or diver–to–diver communications, this more compact structure is the preferred design.

 

The feasibility of remotely sensing marine sediments using a parametric array

PA Lepper and B Woodward

Abstract: The design, development and testing of a parametric sonar system was carried out during two multidisciplinary international projects to investigate the feasibility of remote sensing of marine sediments using acoustics. Developments included improved drive signal generation for phase steering the sonar beam, and the implementation of a dynamic stabilisation technique to compensate in real time for wave–induced motion of a tow–fish deployed behind the tow–fish deployed behind a survey ship. This ensured that the transmitted acoustic signals could be detached by a streamer array behind the tow–fish. Sea trials demonstrated the potential for the use of a parametric source to sense, and eventually to characterise, marine sediment geophysical properties.

Technical Briefing

SotonAUV: the design and development of a small, manoeuvrable autonomous underwater vehicle

J Aktman, M Furlong, A Palmer, A Phillips, SM Sharkh and SR Turnock

Abstract: The University of Southampton’s entry into the Student Autonomous Underwater Challenge – Europe (SAUC–E) 2007 was a sutom designed and built autonomous underwater vehicle (AUV) named ‘SotonAUV’. Originally developed for SAUC–E 2006, the vehicle was significantly upgraded for the 2007 competition. The mechanical design of the vehicle is described, and an overview of the autonomy and control approaches employed is provided. The updated vehicle successfully competed in SAUC–E 2007, winning first place in the overall competition and taking the BAE Systems prize for innovation in autonomy.

Book Reviews

Archaeological Oceanography by Robert D Ballard

Reviewed by G Momber

Underwater Technology Vol 28 No 2

Spring 2009

A Personal View

Ocean geo–engineering: science in the spotlight

E Hill

Technical Papers

The use of towed camera platforms in deep–water science

DOB Jones, BJ Bett, RB Wynn and DG Masson

Abstract: Towed camera platforms have been important in the study of the deep sea for over 30 years. The use of towed camera platforms in deep–water science is reviewed, drawing from the experiences of the National Oceanography Centre, Southampton’s (NOCS) towed cameras, the wide–angle seabed photography (WASP) vehicle and the seafloor high–resolution imaging platform (SHRIMP). Practical considerations for towed camera platform use are outlined with particular reference to sensors, flying altitude and comparison between photographs and video. Although the technology for towed camera platforms will change over time, the concept remains of great value in studying the remote deep–sea environment.

 

The effects of high altitude on relative performance of dive decompression computers

PL Buzzacott and A Ruehle

Abstract: In this paper, dive computer generated no decompression limits (NDLs) in fresh water at high altitude were compared with low–altitude single, repetitive and multilevel dives. All computer–generated high–altitude NDLs exceeded those published for the altitude dived. Computer rankings by conservatism for single dives at low altitude had negative correlation with rankings high altitude (r = –0.81). Correlation between high–altitude square–profile dives and low–altitude repetitive, multilevel NDLs was significantly higher (r = 0.91, p < 0.01). We conclude sea–level single–dive NDLs, such as those published in instruction manuals, are not reliable when gauging the conservatism of dive computers for use at high altitude. It is recommended that divers using dive computers for planning high–altitude dives to consider computer–generated real–time NDLs as experimental.

 

Off–gassing of volatile hydrocarbons in hyperbaric environments

V Flook

Abstract: The paper summarises work, carried out on behalf of diving and manufacturing companies, related to volatile hydrocarbon off–gassing in saturation diving systems. In the hyperbaric environment, the problem of off–gassing is compounded by the fact that the divers are exposed to the chamber atmosphere 24 hours a day, 7 days a week, for several weeks, thus exposure limits have to be set much lower than in industry in general. The diving systems themselves are monitored regularly, but work has been carried out to evaluate off–gassing form some of the products used in saturation diving. These include the paints used in chambers, the umbilicals used to supply gas to the diver under water, cleaning agents and new materials planned for use in the new dive systems currently being built.

 It is evident that some materials do off–gas considerable levels of volatile hydrocarbons. Some substances, such as paints, sealing compounds and cleaning agents, off–gas to an extent that would be unacceptable even under normobaric conditions. The soft furnishing materials that were tested off–gassed at acceptably low levels, however, modifications were required to the manufacturing process of bell umbilicals in order to get off–gassing down to an acceptable level.

 Material Safety Data (MSD) sheets are not required to take account of potential off–gassing; indeed, the vapour phase from substances is virtually ignored in the listing of important compounds. This mean s that MSD sheets cannot be used as a guide to safety of the gas phase. New materials destined for diving systems should be tested for off–gassing. It would seem prudent to continue to make routine checks on the diving system during diving operations.

 

Estimation of high data rate underwater acoustic communication channel capacity

Guoqing Zhou and Taebo Shim

Abstract: Underwater acoustic channels (UACh) require robust techniques to obtain high speed data transmission to reliable communication. This paper presents the adaptive transmission technique, in conjunction with the maximal ratio combining (MRC) diversity technique, to adapt UACh fluctuation based on a statistical channel model. Simulation analysis shows that the data rate can be optimised allowing transmitted power to vary with signal–to–noise ratio (SNR), subject to average power constraint. It also shows that the data rate can be increased under adaptive techniques in conjunction with two–branch diversity. Under the optimum data rate, the Matlab simulink of the UACh quaternary phase–shift keying (QPSK) communication system provides a benchmark for experiment to be carried out in the actual environment.

Book Reviews

The History of Oilfield Diving: An Industrial Adventure by Christopher Swann

Reviewed by B Jones

Underwater Technology Vol 28 No 3

Summer 2009

A Personal View

Subsea Technology – Where Next?

I Gallett

Technical Papers

The Nereus hybrid underwater robotic vehicle

AD Bowen, DR Yoerger, C Taylor, R McCabe, J Howland, D Gomez–Ibanez, JC Kinsey, M Heintz, G McDonald, D Peters, C Young, J Buescher, B Fletcher, LL Whitcomb, SC Martin, SE Webster and MV Jakubata

Abstract: The Nereus vehicle will enable scientists to explore remote regions of the oceans, such as under the polar ice caps and deep trenches, up to depths of 10 972m (36 000ft). Technology limitations have prevented routine, cost–effective access to these remote regions, and the final 4500m of the ocean remain largely unexplored. New solutions to deep diving are described. The Nereus hybrid remotely operated vehicle (HROV) is designed for exploration and research needs as a single system. It can operate as an autonomous vehicle for seafloor surveys, or in a tethered/ROV mode to sample rocks or deep–sea animals The HROV Nereus transforms between its two modes of operation to accomplish all these tasks during a single cruise deployment. Sea trials of Nereus took place off the Hawaiian Islands at 2500m in November 2007. An overview of the vehicle and results from its initial trials are reported here.

 

Autosub6000: its first deepwater trails and science missions

S McPhail, M Furlong, V Huvenne, J Perrett, M Pebody and P Stevenson

Abstract: In September 2007 on RRS Discovery, the Autosub6000 autonomous underwater vehicle (AUV) completed its first deepwater engineering trials and, fitted with a multibeam bathymetric mapping sonar, carried out its first science missions less than a year later as part of a geology and geophysics science cruise onboard the RRS James Cook. This paper describes how the issues of energy storage, navigation and buoyancy control were tackled that specifically affect a deep–diving AUV, capable of operating with true autonomy independently of the mother ship.

 

A review of sublittoral monitoring methods in temperate waters: a focus on scale

HB Van Rein, CJ Brown and R Quinn

Abstract: A plethora of methods to monitor shallow sublittoral benthic habitats and communities are available to the marine researcher today. The most widely used methods are reviewed and evaluated, with reference to the spatial scale at which they operate. For ease of comparison, methods are categorised as operating over broad (>1km), meso (10m 1km) and fine scales (<10m). A measure of efficiency and data resolution are provided by exploring the range of sampling techniques and strategies at each of these spatial scales. Recommendations are made regarding which methods are most effective at each scale: light detection and ranging (LIDAR) and multibeam sonar over broad scales; sidescan sonar, drop–down cameras, towed cameras and remotely operated vehicles (ROVs) over meso scales; and grab samplers, sediment corers for soft, unconsolidated sediments and photoquadrats, and video transects for hard, consolidated sediments at fine scales. Emphasis is placed on the development of standardised methodologies for sampling each scale within a nested design, for the monitoring programmes of the future.

 

Underwater wet welding made simple: benefits of Hammerhead® wet–spot welding process

D Keats

Abstract: A new method of wet welding was investigated to evaluate potential improvements in weld quality, ease of use, increased welding speed and the elimination of welding skill. The new welding process, which has been called Hammerhead `wet–spot’ welding, eliminates the need for skilled welder–divers as well as traditional cleaning and preparation techniques normally associated with conventional manual metal arc (MMA) wet welding. In addition, the process also allows welding to be conducted in nil visibility, yet remains a MMA process, using a specially designed Fe Cr Ni Mo electrode. The process utilises a control device, which must be pre–set before the diver enters the water. Through this device, weld parameters are controlled and quality is maintained, thus the role of the diver is simplified to three steps: make contact with the material, strike the arc and maintain pressure to the electrode while welding. A series of spot welds were produced both wet and dry on 8.0mm carbon steel plates. The welds were evaluated with regard to ease of use and setting up of the device, speed and final weld quality. Initially, the performance of the process was assessed and usage diagrams produced. Work regarding an automated version of the system has also been proposed.

Meeting Note

Selected Summary Highlights from the 30th Consultative Meeting (LC30) of Contracting Parties to the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972 (London Convention 1972) and the 3rd Meeting of Contracting Parties to the 1996 London Protocol (LP3) to the London Convention (London Protocol), 27 31 October 2008 in London at the International Maritime Organization

P Verlaan

Book Reviews

The Andaman Express by Lorne Gifford

Reviewed by I Gallett

Underwater Technology Vol 28 No 4

Unmanned Underwater Vehicle Showcase Special Issue

Autumn 2009

Guest Editor’s Note

UUVS Special issue on navigation, guidance and control of unmanned underwater vehicle

R Sutton

Technical Papers

Towards supervisory–switched control of hybrid underwater vehicles

AJ Sørensen and J Refsnes

Abstract: The paper presents automatic control system design considerations for underwater vehicles conducting a diversity if intervention and inspection missions. Such multitasking vehicles are here denoted as ‘hybrid underwater vehicles’. Dependent on the various operations, the vehicle particulars – such as mass, breadth, length or centre of gravity – may change considerably due to changing payloads, such as tool and instrumentation packages. This can lead to both structural and parametric model variations that will be time–varying, though partly known, depending on the given mission. Both the modularity in the controller design and the ability to switch between the appropriate banks of controllers enable the design of automatic supervisory–switched control systems. This paper also presents recent research work at the Norwegian University of Science and Technology (NTNU) on nonlinear model–based control of slender–body underwater vehicles. In particular, results from a study using a Minesniper MKII will be discussed, describing two of the model regimes as proposed for supervisory–switched control concept.

 

Fòlaga: a low cost AUV/glider for coastal environmental sampling

A Caffaz, A Caiti, G Casalino, L Gualdesi and A Turetta

Abstract: The paper describes the current evolution of the class of Fòlaga underwater vehicles, whose actuation mechanism is hybrid between oceanographic gliders and standard, self–propelled autonomous underwater vehicles (AUVs). The Fòlaga vehicles have been designed for coastal oceanography and environmental sampling: the application–oriented design approach has resulted in light–weight, low–cost, low–maintenance vehicles. A description of the vehicles’ design and guidance, navigation and control capabilities is given, together with data from recent experimental trials.

 

A flexible multi–mode of operation, high resolution survey platform for surface and underwater operations

D Toal, S Nolan, J Riordan and E Omerdic

Abstract: This paper describes the ROVLATIS, a multi–mode of operation flexible platform for high–resolution near–seabed survey from shallow inshore waters to depths beyond 1000m. The paper further describes the operation modes of the vehicle. Special system features include: deployment flexibility for both small inshore boats and larger research vessel; fault tolerant controls; onboard computer control enabling real–time disturbance reaction, autopilot functionality and autonomous underwater vehicle (AUV) experimentation; and topside augmented reality operations support, simulation for remotely operated vehicle (ROV) pilot and sonar operator/hydrographer training. Vehicle and control development using the University of Limerick (UL) virtual underwater laboratory/simulation tools and hardware–in–the–loop testing is described. The paper includes test results from the March 2009 offshore sea trials with the ROVLATIS.

 

Underwater vehicle technology in the European Research Project VENUS

G Conte, L Gambella, D Scaradozzi, S Zanoli, A Caiti, V Calabrò, A Alcocer, J Alves, B Cardeira, R Cunha, F Curado, P Oliveira, A Oliveira, A Pascoal, M Rufino, L Sebastião and C Silvestre

Abstract: This paper describes the work carried out during the first part of the European research project Virtual ExploratioN of Underwater Sites (VENUS) by two of the participating teams. As the project is aimed at developing a set of best practices, procedures and tools for exploring underwater archaeological sites, part of the work concentrated on the use of unmanned underwater vehicles for gathering optical and acoustic data on field and their use in constructing photographic maps. At the same time, the use of unmanned surface vehicles for long–range exploration and construction of large–scale acoustic maps was investigated.

      Concentrating the first point, the main results consist of a series of best practices and procedures for collecting correlated and geo–referenced optic and acoustic images, which are used for constructing online two–dimensional photographic maps of the explored area during the survey, as well was offline three–dimensional representation of the site in a virtual reality environment. The construction of two–dimensional photographic maps represents a major innovation towards conducting archaeological exploration and defines a new, efficient way of governing it, at logical level, in a closed loop fashion. Integration of the information into a geographic information system (GIS) has also been developed to help archaeologist interpret the results of the ongoing exploration with respect to larger scenarios, and possibly to modify or adjust the mission parameters during its execution accordingly. The basic capability of surface vehicles in connection with the objectives of the archaeological exploration has been investigated as a basis for an integration between underwater and surface vehicles in that activity.

Book Review

Masterclass in AUV Technology for Polar Science edited by Gwyn Griffiths and Ken Collins

Reviewed by J Evans

Underwater Technology Vol 27 No 1

Winter 2007

 A Personal View

Some inconvenient truths

Author

Technical Papers

Underwater technology and international patent strategies from a US perspective

W Buskop

Abstract: Inventions for underwater technology can include a variety of new subsea innovations, such as methods for placing moorings, manufacturing of hydrophones, using remotely operated vehicles (ROV) in a new way, a new lighting device to illuminate underwater drilling, underwater test equipment, controls systems, quick disconnects and fancy new diving flippers. Protecting this technology in the United States, and internationally in the countries of the 134 members of the Patent Cooperation Treaty (PCT), is an expensive and sometimes seemingly endless process.

 

Decoupled modelling and controller design for the hybrid autonomous underwater vehicle: MACO

J Kennedy, E Gamroth, C Bradley, and AA Proctor

Abstract: Researchers at the University of Victoria have developed a hybrid autonomous underwater vehicle (AUV) named MACO capable of three–dimensional keeping and manoeuvring without forward velocity. This makes it suitable to perform many of the tasks traditionally accomplished by remotely piloted underwater vehicles. Once operational, MACO was used in a Defence Research and Development Canada (DRDC) feasibility study for using AUVs to support rapid deployment of acoustic element arrays. The AUV was required to stop and hover, while triggering a low frequency sound source. The performance of the MACO during these sea trials is presented as the conclusion to this paper.

 

A determination of the propagation of electromagnetic waves through seawater

J Lucas and CK Yip

Abstract: For the past four years detailed experiments have been carried out to investigate the propagation of electromagnetic (EM) waves between antennae in seawater in the MHz frequency range. The results have clearly shown that propagation is possible over a distance of 100m in a Liverpool Dock for frequencies in the range 1 to 5MHz using a 30W amplifier. The existing water/air/water model of propagation cannot explain this result. Therefore a theoretical model is given in this paper to explain the result and to give a generalised solution. It is based upon the generation of EM waves by dipole oscillations of the water molecules within the antenna electric field. The model has explained all the features observed in detailed experimental results obtained in tank experiments with both tap and salt water, whose conductivity varies between 0.1 and 4S/m, as well as in trials within Liverpool Dock. Within the tank the received signal in tap water increases with increasing frequency, whilst in salt water it decreases with increasing signal frequency. In general the signals in seawater are –55dB lower than in tap water. For each frequency the signal strength in seawater during propagation shows a rapid decrease in the vicinity of the transmitting antennae (near field) but only shows a slow decrease in the far field. The slow decay in the far field is attributed to a combined diffraction loss and an attenuation loss that increases with frequency. The result in the received signal exhibits a resonant effect in the frequency range 10 to 20MHz for propagation in seawater for a distance of 100m. Lower and higher MHz frequencies are difficult to propagate because the received signal strength is comparable with the background electrical noise within seawater (–135dBm) when a 30W signal is transmitted.

Meeting Reports

Selected Summary Highlights from the 54th Meeting for IMO’s Marine Environment Protection Committee (MEPC 54), 20–24 March 2006

P Verlaan

 

Selected Summary Highlights from the 28th Consultative Meeting (LC 28) of Contracting Parties to the Convention on the Prevention of Marine Pollution by Dumping of Wates and Other Matter 1972 (London Convention 1972) and the 1st Meeting of Contracting Parties to the 1996 London Protocol (LP 1) to the London Convention (London Protocol: LP) 20 October–3 November 2006 in London

P Verlaan

Book Review

Homo Britannicus; the incredible story of human life in Britain by Chris Stringer

Review by N Flemming

Underwater Technology Vol 27 No 2

Winter 2007

A Personal View

Forty Years of SUT

I Gallett

Technical Papers

Insurance for autonomous underwater vehicles

G Griffiths, N Bose, J Ferguson, DR Blidberg

Abstract: The background and practice of insurance for autonomous underwater vehicles (AUVs) are examined. Key topics include: relationships between clients, brokers and underwriters; contract wording to provide appropriate coverage; and actions to take when an incident occurs. Factors that affect cost of insurance are discussed, including level of autonomy, team experience and operating environment. Four case studies from industry and academia illustrate how AUV insurance has worked in practice. The paper concludes by stressing the importance of effective dialogue between client, broker and underwriter to review, assess and reduce risk to the benefit of all parties.

 

The influence of energy extraction from open channel flow and its impact on tidal current energy system design

JP Chick, IG Byrden and SJ Couch

Abstract: This paper explores the sensitivity of a simple model of open flows, which has been developed to facilitate the preliminary assessment of the suitability of tidal channels for energy exploitation. Using models deliberately simplified for clarity, the sensitivity is shown to be dependent primarily upon length, depth and boundary roughness. The model results are then used to support the use of a non–dimensional number which may prove useful in future classification of the sensitivity of tidal channels. Energy extraction from a tidal stream is shown to have the potential for significantly altering the flow through the channel in question and, in doing so, imposes constraints on the design of the extraction system itself. This differs significantly from the practice of resource assessment in the wind energy industry.

 

Automatic seabed texture segmentation and classification based on wavelet transform and fuzzy approach

R Javidan and HJ Eghbali

Abstract: This paper deals with segmentation and classification of textual images of seabed using wavelet domain features and modified split and merge algorithm based on fuzzy approach. The original image is first analysed using a fuzzy edge detector to improve the differentiation between different texture types. Simultaneously, two–level standard wavelet transform is applied to the original image. The high frequency detail coefficients produced from the six sub–bands of the wavelet and the image produced by the fuzzy edge detector are divided into M x M blocks. Energy of each block is calculated and a minimum distance classifier is used for each wavelet and fuzzy block to classify (and segment) the original image in a hierarchy of three levels of resolutions. The classified blocks of the two segmented images produced by the wavelet transform are merged and refined based on degree of edge certainty acquired form the fuzzy algorithm to construct the final segmented image. In this research, it is shown that energies of the wavelet coefficients are powerful features for discrimination of different seabed textures. The classification results of the energy features of the wavelet coefficients are compared with the results of other features of the wavelet coefficients to show the fidelity of this feature. The proposed approach provides a fast tool with enough accuracy that can be applied in real–time applications of automatic discrimination of the seabed. Moreover, the simulation results are compared with other well–known methods to show the effectiveness of the proposed algorithm.

Meeting Report

Selected Summary Highlights from the 55th Meeting of the intergovernmental Marine Environment Protection Committee (MEPC 55) of the International Maritime Organisation (IMO), 913 October 2006, held at Central Hall Westminster, London

P Velaan

Book Review

Lost Treasure Ships of the Northern Seas: A Guide and Gazetteer to 2000 Years of Shipwreck by Nigel Pickford

Reviewed by R Rogers

Underwater Technology Vol 27 No 3

Scientific and Archaeological Diving Special Issue

Autumn/Winter 2007

A Personal View

The past, present and future for scientific diving

MDJ Sayer

Technical Papers

Scientific diving: bibliographic analysis of underwater research supported by SCUBA diving 1995–2006

MDJ Sayer

Abstract: There is little quantitative information by which to assess the recent importance of diving to the scientific community. This review is a bibliographic analysis of the papers published from 1995 to 2006 that have been supported by scientific diving. Diving supports scientific research through efficient and targeted sampling (including numerous new species and reports), quantitative survey, observing animal behaviour, making in situ measurements, undertaking impact studies, a variety of ecological analyses, the evaluation of new techniques, by mapping underwater areas, profiling subtidal geology and by deploying and retrieving underwater apparatus. Each section is reviewed in detail. However, by comparing the database searches against a selection of publications known to have used scientific diving in the same period, possibly only 7% (with 96% confidence limits of 0–15%) od papers were captured. It is suggested that the significance of scientific diving is vastly unrepresented by the literature and that the divers themselves should try to ensure proper acknowledgment in order to preserve and promote scientific diving as a valid and cost effective underwater research tool.

 

Scientific diving in the United States: the value of SCUBA as research methodology

M Lang

Abstract: The US scientific diving regulatory, medical, training and operational framework has resulted in a remarkably low decompression sickness incidence rate. In this particular segment of the diving community, diving safety research on dive computers, ascent rates, multi–day repetitive diving, polar diving, reverse dive profiles, oxygen–enriched air and advanced scientific diving contributes to the conservative risk management approach of scientific diving. The importance of scientific diving as a valuable research tool by placing the trained scientist’s eye under water is illustrated by a number of Smithsonian Institution research projects that could otherwise not have been performed, with results published in the scientific literature. The peer–review publication process validates the viability and effectiveness of SCUBA as a research methodology.

 

The investigation of submerged Stone Age Landscapes using diving as a research tool: an example from Denmark

O Grøn

Abstract: Diving offers a research tool that permits access to well–preserved submerged sites of highly significant archaeological and cultural interest. As an example, this account presents a summary of an excavation of a dwelling and a grave at a submerged 7000–year–old Danish Stone Age site and discusses the implications of the presence of extremely well preserved Stone Age sites and entire Stone Age landscapes under water. Submerged Stone Age sites may yield a wealth of archaeological information because of the quality of preservation and the relative lack of disturbance. Diving presents an effective tool for unlocking the secrets of these sites.

 

Use of diving computers in brittlestar surveys

KJ Collins and B Baldock

Abstract: Dense beds of brittlestars (Ophiothrix fragilis) were discovered in 1975 in water depths of 10–20m off Broad Beach, Kimmeridge, Dorset, within the Purbeck Marine Wildlife Reserve. Drift dives carried out during 2001–2003 aimed to map the extent of these aggregations. This paper describes the methods employed: tracking drift drives with GPS positions of the dives surface marker buoys in combination with sport diving computers recording time and depth plus ‘events’ (ie, the start and end of aggregations). The combination of GPS and dive computer enabled mapping of these aggregations in three dimensions. The brittlestars were found to be associated with the upper slopes of reef ridges but absent from the summit and troughs. Application of the techniques to biogenic worm reef (Sabellaria spinulosa) and maerl (Phymatolithon calcareum) surveys are described.

 

The influence of census technique on estimating indices of macrofaunal population density in the temperate rocky subtidal zone

MDJ Sayer and C Poonian

Abstract: Several studies have attempted to compare subtidal animal population estimates obtained in a variety of ways using SCUBA diving and have reported a lot of variations between the estimates obtained. This study investigated individually scale–, tidal–, equipment– and observer–induced variation through analysis of animal population density indices obtained using a number of techniques based on SCUBA diver visual survey. The study was based on shallow subtidal sites on the west coast of Scotland including natural rocky slopes and recently deployed artificial reef sites. Groups of species investigated varied in levels of size, abundance, mobility and detectability. Variability in estimated densities between different sizes of sampling unit, state of tide, type of SCUBA equipment used (open circuit versus rebreather) and observation technique was found to be considerable. A decreasing asymptotic relationship with quadrant size was evident in the majority of cases for estimated density, coefficient of variation and number of samples required to attain a given precision. However, the size of the sampling unit employed  had to be large enough to encompass the variability in spatial distribution of the target organism. Improved precision for estimates of cryptic species was obtained from relatively small sampling units, which focused the observer’s attention onto a specific area. Underwater photography as a population estimation technique produced data comparable with that from visual surveys but was limited by the size of the sampling unit. The use of remotely deployed infrared video demonstrated that certain animal species and life–stages actively avoid divers and were largely absent from the diver–based surveys. Although larger quadrants generated more precise estimates, the longer sampling times involved reduced their overall efficiency for most groups surveyed; optimum sampling unit sizes are suggested for particular animal groups.

Tech Briefing

The use of archaeological diving, survey and literature–based techniques to evaluate potential protected status for shipwrecks

DM McElvogue

Abstract: Unlike military aircraft, shipwrecks do not automatically gain protected status under the 1986 Protection of Military Remains Act. Irrespective if whether or not there was any loss of life or whether the wrecking occurred during peacetime or in combat, the determination of protected status for shipwrecks, commonly referred to as designated war graves, usually depends on a judicial review process. Where there is no good historical evidence to support the case for protection, the determination of status may then be based on information obtained from present–day surveys. This technical note gives an overview of how archaeological survey methodologies can be employed in attempting to provide evidence to support, or otherwise, a claim form protected status. This account is based on the example of the SS Storaa.

Book Review

The Profession Diver;s Handbook, Second Edition – by John Bevan PhD

Reviewed by DR Shiers

Underwater Technology Vol 27 No 4

Oceanography International Special Issue

Spring/Summer 2008

A Personal View

The threat and promise of methane hydrates

D Hazelwood

Technical Papers

The progression and impact of the latest generation of multibeam acoustics upon multidisciplinary hydrographic–based applications

C Malzone, D Lockhart, T Meurling and M Baldwin

Abstract: The progression of hydrographic echo sounding has been driven by navigational, socioeconomic (EEZ, Law of the Sea, Offshore Oil/Gas) and research (habitat mapping, coastal erosion, etc) requirements. Since the first installation of a multibeam echo sounder (MBES) in 1963, the progression of the technology has provided a steady increase in the number of soundings, as well as increases in sampling rates, data volumes and system resolution. Recent improvements incorporate better signal–to–noise ratios, multiple frequencies, calibrated arrays and new signal processing functionality. These advancements, combined with parallel improvements in data acquisition methods and post–processing techniques, make the data more accurate, thus providing more reliable survey products. MBES technology now makes use of all aspects of the inherent acoustics to provide additional data products, such as beam intensity, pseudo–sidescan, seafloor backscatter and raw time series backscatter. The latest generation of MBES now contains the processing power to log concurrently all datagrams with the same sampling and ping rates as the International Hydrographic Organization (IHO) Special Order bathymetry data (34.5kHz and 40Hz, respectively). The result has been the incorporation of multibeam derived products for multidisciplinary hydrographic–based applications, such as nautical charting, habitat mapping, fisheries biomass surveys and sediment transport studies. This paper explores recent improvements in MBES systems in comparison with their older counterparts and discusses the effects these advancements will have on the future of multidisciplinary hydrographic–based applications in both shallow and deep waters.

 

Environmental impact and appraisal – planning consent for the South West of England Wave Hub

N Harrington and I Andina–Pendás

Abstract: Wave Hub is an innovative demonstration site for generation of wave energy located in the South West of England. In simple terms, Wave Hub consists of an offshore electrical ‘socket’ to connect arrays of wave energy converters to the national grid via undersea cables, allowing technology developers to demonstrate and monitor the operation of their devices in real sea conditions. A key element in the development of the proposed Wave Hub was to gain consent from the relevant UK regulatory bodies. This paper describes the process for the consent application followed and highlights the main issues encountered during the preparation of the environmental studies to support the application, and subsequent discussions with regulators and stakeholders.

 

Improved measurement technologies for floating wave energy converter (WEC) mooring arrangements

L Johanning and GH Smith

Abstract: Large–scale experiments were conducted under real sea conditions to support the investigation of non–linear mooring line effects and their importance to moored wave energy device installations. The problems associated with such testing are described, and a discussion of solutions to overcome these is given. An improvement of the experimental apparatus and procedures resulted in meaningful data that could be compared with tank testing and numerical models. The lessons learned have provided confidence in the future implementation of an offshore mooring test facility off the Cornwall coast.

 

Synthetic aperture 3D buried object imaging

S Schock

Abstract: A towed synthetic aperture sonar called buried object scanning sonar (BOSS) performs synthetic aperture processing and generates orthogonal projections of 3D subsurface data to view objects buried in the seabed. The development of BOSS is reviewed, including significant results. During an experiment in St Andrews Bay, Florida, the latest version of BOSS, called BOSS–160, generated images of small cylinders (simulating ordnance) buried at two shallow water sites with 3m water depths, and with sand and muddy sand bottom types. Image projections show the orientation, length and burial depth of cylinders with diameters of 5, 7.5, 10 and 15cm.

 

The role of autonomous underwater vehicles for marine search and rescue operations

AJ Murphy, MJ Landamore and RW Birmingham

Abstract: There is an ever–increasing adoption of new technologies to improve safety of life, and autonomous technology is no exception. The use of robotic machines for assisting in search and rescue (SAR) operations is evident in land and air based scenarios, and European calls for research into the use of remotely operated or autonomous systems specifically address this requirement for marine based search and rescue. This paper addresses the current state of autonomy in the search and rescue field, as well as the current technologies available for marine applications. A concept for using autonomous underwater vehicles (AUVs) in marine search roles for SAR scenarios is provided, and the feasibility of such a system is demonstrated. Existing commercially available AUVs are shown to be capable of providing a viable search area coverage rate, and sensor technology is sufficiently mature to enable detection of survivors from the proposed autonomous platform. The technical challenges for further development of the concept are also addressed.

 

The role of autonomous underwater vehicles for marine search and rescue operations

AJ Murphy, MJ Landamore and RW Birmingham

Abstract: There is an ever–increasing adoption of new technologies to improve safety of life, and autonomous technology is no exception. The use of robotic machines for assisting in search and rescue (SAR) operations is evident in land and air based scenarios, and European calls for research into the use of remotely operated or autonomous systems specifically address this requirement for marine based search and rescue. This paper addresses the current state of autonomy in the search and rescue field, as well as the current technologies available for marine applications. A concept for using autonomous underwater vehicles (AUVs) in marine search roles for SAR scenarios is provided, and the feasibility of such a system is demonstrated. Existing commercially available AUVs are shown to be capable of providing a viable search area coverage rate, and sensor technology is sufficiently mature to enable detection of survivors from the proposed autonomous platform. The technical challenges for further development of the concept are also addressed.

 

Development and field testing of the Doppler Volume Sampler

PE Plimpton and JW Mullison

Abstract: In 2004 the Pacific Marine Environmental Laboratory (PMEL) sponsored a Request for Proposals (RFP) from industry to develop a new instrument that combined ocean current measurements, highly accurate temperature measurements and inductive communication in a single package. To support global ocean monitoring, the new instruments would be deployed on PMEL’s deep ocean surface moorings at selected depths from the near surface to 750m, with data telemetered to shore via satellite in near real time. From the proposals submitted, PMEL selected the Doppler Volume Sampler (DVS), a point current meter developed by Teledyne RD Instruments, for testing. This paper discusses the DVS engineering design, measurement capabilities, including features for data quality assessment, and the testing performed during the instrument evaluation.

Meeting Report

Subscribed Content Selected Highlights of the 29th Consultative Meeting (LC 29) of Contracting Parties to the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972 (London Convention 1972) and the 2nd Meeting of Contracting Parties to the 1996 London Protocol (LP 2) to the London Convention (London Protocol; LP), held at the Headquarters of the International Coffee Organization, 5–9 November 2007 in London

P Verlaan

Book Review

Admiralty Salvage in Peace & War 1906–2006: ‘Grope, Grube and Tremble’ – by Tony Booth

Reviewed by J Bevan

Underwater Technology Vol 26 No 1

A Personal View

Who should bear the cost of quality?

R Pond

Letter

A regional initiative to manage the Bay of Bengal’s coastal and marine environment and its living resources

P Verlaan

Review

Lander techniques for deep–ocean biological research

PM Bagley, IG Priede, AD Jamieson, DM Bailey, EJV Battle, C Henriques and KM Kemp

 

Excess pore pressures induced by installation of suction caissons in NC clays

J Cao, R Phillips, R Popescu, JME Audibert, Z Al–Khafaji

 

Laser stripe imaging to determine three–dimensional information on fish shoals

S Tetlow, S Creaven, EG Jones and DG Reid

 

Mapping seabed biotopes using sidescan sonar in regions of heterogeneous substrata: Case study east of the Isle of Wight, English Channel

CJ Brown, AJ Hewer, WJ Meadows, DS Limpenny, KM Cooper and HL Rees

 

Interfaces between the submarine cable industry and other seabed users around UK coastal waters

N Irvine and R Borwick

 

Technical diving

M Caney

Book Review:

The Sea’s Enthrall: Memoirs of an Oceanographer, by Dr Timothy Parsons

Reviewed by M Angel

Underwater Technology Vol 26 No 2

Summer 2005

A Personal View

Marine Renewables — Will the UK drop the ball (again)?

P Wolfe

Technical Papers

Trends in scientific diving: an analysis of scientific diving operation records, 1970–2004

MDJ Sayer and J Barrington

 

Closed loop identification of a remotely operated flight vehicle

M Wang and R Sutton

Technical Briefings

The use of renewable energy systems in coastal defence

JW Griffiths, DE Lennard R Kirby, T Thorpe

 

Seabed coring in the ice–covered waters of the Arctic Ocean for the Integrated Ocean Drilling Program

D Evans and A Skinner

Meeting Reports

Current status of marine minerals

David Cronan

 

The 6th Renewable Energy Finance Forum (REFF) and marine renewables

Don Lennard

Book Reviews

Dive, Dive, Dive — Submarines at war, by Michael Gunton

Reviewed by DR Wardle

 

Raising the Kursk, by Hans Offringa

Reviewed by Roger Chapman

Underwater Technology Vol 26 No 3

Winter 2005

A Personal View

The role of Subsea UK

DL Pridden

Letter

Second letter from Madras: Progress in the Bay of Bengal Large Marine Ecosystem (BOBLME) Programme

P Verlaan

Review

A review of the uses of work–class ROVs for the benefits of science: Lessons learned from the SERPENT project

IR Hudson, DOB Jones and BD Wigham

Abstract: This paper reviews the contributions of underwater science in continuing to develop new technology to explore the marine environment and how collaborations taking place between the oil and gas industry and science are facilitating this process. A case study focuses on some of the results and highlights from the SERPENT Project. SERPENT (Scientific and Environmental ROV Partnership using Existing Industrial Technology) is a collaboration programme that was designed to make better use of remotely operated vehicle (ROV) technology and data available through links with marine operations in the oil and gas industry. Oil and gas exploration and production activities in the marine environment are increasing. The amount of global hydrocarbon reserves removed from below the seafloor is set to increase over the next 5–10 years with exploration heading into deeper, more remote waters, many of which have yet to be fully explored. The only way that these remote areas may be documented is through a working relationship with industry, with mutual benefit for both sides, and learning from technology that is already in place for the benefit of science.

Technical Papers

Research on the pressure compensation for the underwater hydraulic motor

YM Li and QF Wang

Abstract: Considering the influence of underwater ambient pressure (UAP) on underwater hydraulic motors (UHM), and utilising the state–of–the–art of pressure compensation of underwater hydraulic systems (UHS), this paper proposes a pressure compensation technique for the UHS where the hydraulic power unit is installed inside a deep diving submersible or a submersible drilling platform with atmospheric pressure, some actuators of which are directly surrounded by seawater and others are installed inside it. An underwater ambient–pressure–compensation valve (UAPCV) has been developed. The pressure in the return line of the external sub–circuits of the UHS is compensated by this UAPCV, but not that of the internal sub–circuits. Theoretical analysis, simulation and experimental results show that reliable pressure compensation can be ensured with a small flow–rate by the UAPCV. The operational performance of the UHM is further improved after its leakage pressure and return pressure are compensated.

 

Estimation of underwater noise – a simplified method

RA Hazelwood and J Connelly

Abstract: A set of procedures has been developed to allow preliminary estimates to be made of underwater noise and its effects on marine species. They do not require detailed acoustic survey data, either of the site or of the proposed plant. However, they still facilitate the comparison of different project proposals to assist in the optimisation of equipment layout and routing. Noise may be due to specific sources, such as ships and marine equipment, or assessed as a general background level. Some aspects of acoustic analysis applicable to more detailed environmental impact assessments are also described, particularly relevant when comparing noise spectra with audiometry data appropriate to different species of wildlife.

 

The use of fault tree analysis to visualise the importance of human factors for safe diving with closed–circuit rebreathers (CCR)

S Tetlow and S Jenkins

Abstract: Closed–circuit rebreathers (CCR) have been used for many years in military diving but have only recently been adopted by technical leisure divers, media and scientific divers. Rebreather divers appreciate the value of training, pre–dive checks and equipment maintenance, but it is often difficult to visualise just how important these factors are and how they inter–relate for a rebreather. In this paper, the well–known technique of fault tree analysis (FTA) is used to identify risk in a rebreather. Due to space constraints, only the branch of the tree for unconsciousness as a result of hyperoxia is considered in detail but, in common with the whole tree, end events are shown to be human–factor related. The importance of training to the emergency situation, the use of formal pre–dive checklists and the value of good design to prevent accident escalation are discussed further.

 

Results of cylinder detection and fitting from real three–dimensional underwater acoustic images

RC Patel and AR Greig

Abstract: For remotely operated underwater vehicles operating in the vicinity of offshore platforms, the object recognition and detection of cylinders is of importance because many platforms are constructed from connected tubular elements. This paper briefly reviews acoustic cameras and then presents a cylinder–based model matching procedure for 3D underwater acoustic camera images. Cylinder identification is achieved using a combination of information from the 3D acoustic image and the 2D intensity map. The paper concludes with some sample results of images of a scaled oilrig structure captured using a 3D acoustic camera.

Book Reviews

Oceans 2020: Science, Trends, and the Challenge of Sustainability

Reviewed by T Guymer

Underwater Technology Vol 26 No 4

Summer/Autumn 2006

A Personal View

Supporting new waves in marine technology

L Slade

Technical Papers

Transient free–surface waves due to impulsive motion of a submerged source

J–J Shu

Abstract: The problem of a viscous flow past a submerged source starting from rest and moving with a constant velocity, below and parallel to a free surface, is examined and asymptotic expressions for long–time evolution of free–surface elevation are obtained. The results show explicitly the viscous effect on the free–surface elevation and no surface tension effect on the asymptotic wave.

 

Extracting the cultural heritage: new challenges for the underwater archaeologist

G Momber

Abstract: Analysis of archaeological sites stratified within marine sediments can open a window to cultures that are now lost between the waves. These sites and their environmental context harbour a resource that can also provide index points for sea level rise during a period of acute climate change. A decade of archaeological investigations in the western Solent by the Hampshire and Wight Trust for Maritime Archaeology, utilising divers and geophysical survey data, has led to the discovery of Mesolithic sites within submerged landscapes. They lie between 6.5m and 11.5m below British Ordnance Datum. However, the discovery of these delicate and vulnerable sites is presenting new challenges to the maritime archaeologist. The need to record, rescue and interpret the remains underwater sampling techniques.

Technical Briefing

Sea bass (Dicentarchus Labrax) and a sea change for 21st century fisheries

J Hind

Meeting Reports

Selected Summary Highlights from the 53rd Meeting of the intergovernmental Marine Environment Protection Committee (MEPC 53) of the International Maritime Organization (IMO), 18–22 July 2005

P Verlaan

 

Selected Summary Highlights from the 27th Consultative Meeting (LC 27) of Contracting Parties to the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972 (London Convention 1972) held at IMO Headquarters, 24–28 October 2005

P Verlaan

Book Review

Diving and Subaquatic Medicine, by Carl Edmonds et al

Reviewed by J Bevan