The Evolution of a Nearshore Survey Vessel

In recent years an expansion in the telecommunications industry has led to a growing market for cable-route landfall surveys. Added to this, the increasing interest in coastal-zone management (which may require surveys to be conducted) has led to a demand for specialist ‘near shore’survey vessels.

Titan Environmental Surveys Ltd has been specialising in nearshore and shallow-water geophysical, oceanographic and environmental surveys for over ten years. During this period the company has successfully surveyed in many different environments and parts of the world, utilising a variety of vessels of opportunity. Working conditions have ranged from conducting a geophysical survey in baking temperatures on board a rusting harbour tug with no air conditioning in the middle of the summer in Africa, to mapping thermal plumes from a small open boat in sub-zero winter temperatures for a full tidal cycle of thirteen hours.

Birth
Given the difficulties often encountered in sourcing suitable survey vessels, and the need to remain cost-effective in a fiercely competitive marketplace, Titan elected to commission their own inshore survey vessel from Cheetah Marine, based on the Isle of Wight. Working on many different vessels over the years had highlighted the specific design characteristics required for a specialised inshore vessel - the vessel had to be stable with room for all of the required survey equipment; be of shallow draft and fast so as to reduce transit time to and from site and yet still be small and light enough to give the flexibility of easy mobilisation to site by road.
At the end of a lengthy design and consultation period the first of three specialised survey catamarans - Titan Surveyor - was delivered in June 1998 after a six-month build period. A second vessel (Titan Explorer) was delivered in June 1999, and a third (Titan Voyager) in May 2001. All are driven by outboard engines, with inboard generators providing electrical power for equipment, and all are certified to the ‘Brown Code’(the MCA Code of Practice for the Safety of Small Workboats and Pilot Boats). With safety being paramount over any survey requirements all the vessels are equipped with a full range of safety apparatus as requested by the governing body, the MCA, such as EPIRB, VHF/GMDSS radios, life-rafts, radar, etc. In addition, the vessels have additional buoyancy built into each hull in the form of individual, sealed containers so that even if both hulls become holed in the course of duty (which is a constant threat when surveying the most rocky of coastlines) then there is sufficient additional buoyancy for the vessel to remain afloat.
The basic construction of all three vessels is generic:

• Hulls
  
• Superstructure
  
• Bulkheads
  
• Deckheads
  
• Gunwales
  
• Windows
  
• Pods
  

The base design is a GRP catamaran, but with each vessel having been tailored and modified through time so that the three ‘cats’complement each other and some are better suited to some tasks than others.
For its inaugural survey, Titan Surveyor was trailed to Milford Haven in South Wales to conduct a bathymetric and side-scan sonar survey of one of the deepest natural harbours in the world. The logistics of the survey meant that a vessel had to have the speed to cut down on transit time, good fuel economy to maximise time spent on line, shallow draft to ensure that the rocky coastline of Milford Haven was surveyed to the limits of safe working and sea-keeping qualities that would enable operations at the entrance to the Haven, exposed to the weather and open seas from the Atlantic Ocean.

Adolescence
Inevitably, as with most vessels, compromises have had to be made. A vessel that is small enough to be readily towed to site at a moment’s notice has more limited space for survey equipment, personnel and client’s representatives, and has to return to shore for refuelling, crew changes, etc. Conversely, a larger vessel may offer living accommodation for boat and survey crew, and several days of operations before requiring to return to port, but is likely to be too big to be easily transported by road, and may be restricted by larger draft from surveying shallow and difficult waters in the intertidal and immediate subtidal zone.
Since launch, Titan’s vessels have undergone small but important metamorphoses to adapt and improve them to provide the safest working platform for a particular situation. Each vessel starts out as a Cheetah Marine standard catamaran, with a lockable wheelhouse and 19" rack system to house survey equipment. Electrical power is supplied by a marinised diesel generator, and propulsion is via a pair of outboard engines. This basic layout has then been variously modified with each succeeding vessel, and Titan and Cheetah Marine continue to develop the craft to improve the overall package. Modifications have taken the form of:

• Small increases in length of the Titan Surveyor and Explorer, to improve the vessels attitude in the water and increase transit speeds
  
• Various cable ducts added (to ease mobilisation and daily operations)
  
• 19" rack system altered (to increase work surface area)
  
• Stern gear modifications (increased gantry size to ensure towed equipment such as side-scan sonar bodies are removed as far as possible from the motion of the vessel and vessel noise)
  
• Masts and topside metalwork is a maximum of 2m above the wheel-house roof and yet folds neatly away for road transport
  
• Items which need to be side mounted have specially designed brackets and supports which are easily mobilised and de-mobilised
  

The ongoing development and improvement of the vessels is a feature of the close relationship with Cheetah. For the Titan Surveyor, further changes were made to enable her to be launched and recovered from a mother ship for an extensive survey in the Red Sea. Weight had to be minimised to keep the vessel and her launching cradle within the working limits of the deck crane. To this end the Titan Surveyor was refitted with a lightweight diesel generator, lightweight stainless steel 19" racks and diesel outboards as opposed to petrol so that the survey vessel could refuel direct from the mother ship’s tanks.
Inevitably, specific modifications made to a vessel for a particular purpose (as described above for the Red Sea project) can easily become potentially limiting factors on the next project. For instance, the lightweight generator fitted to the Titan Surveyor for the Red Sea was of lower electrical output than the unit it replaced, so on return to the UK an additional power source was required for working with a full spread of equipment for geophysical surveys. The optimum solution is to add a second lightweight generator to the vessel, to power the high-voltage geophysical system (bang box, boomer, etc). Keeping the power supply for this system separate to that for the rest of the survey equipment greatly reduces the likelihood of interference from the high-voltage system affecting other instruments. Although there is a slight penalty in weight, in that the two smaller generators together weigh a little more than one larger unit, the advantages of separate power supplies, the reduced purchase cost of the smaller unit, and the fact that one can be easily removed when not required, strongly outweigh the disadvantages.

Maturity
As the vessels mature, old age will begin to catch up sooner than we all think possible and sight must not be lost of the maintenance of their to ensure a safe and reliable working environment. Often the more equipment is used, the further behind the care and maintenance schedule falls and in such a demanding environment routine maintenance is essential.
All vessels involve a degree of compromise, and our survey catamarans are no different in this respect to other nearshore vessels. However, operations over recent years have demonstrated the soundness of the concept of a light yet stable catamaran as a suitable platform for many aspects of nearshore survey work, and can be supported where required by vessels of opportunity hired to undertake specific operations (e.g. vibrocoring) for which the catamarans are not designed. The success of the vessel’s concept is demonstrated by the fact that other survey companies have subsequently followed the same route, and commissioned their own similar specialised craft for nearshore work. Clearly there is a need for this type of vessel which can be rapidly mobilised to site and can survey in areas most other vessels cannot.