Underwater Vehicles
UNDERWATER A major limiting factor of small shipshaped survey vessels is the wave heights in which they can work. This prompted Chichester-based engineers ASV to design a new unmanned semi-submersible vehicle with, and on behalf of, C&C Technologies. It can carry out operations in wave heights out of the range of many traditional vessels. The first vehicle is currently being transported to C&C Technologies’ base in Louisiana for the next phase of testing. The company contends that this vehicle could result in lower survey costs surveys by not having to employ larger boats.
Enterpris Payload space for sonar, process and storage electronics
Air inlet and communications housing
Called the USS 6300, the unmanned semi submersible is an evolution of the SASS survey and surveillance platform which was designed by ASV back in 2001. It broadly retains the same cruciform shape of its predecessor, although modified to meet specific survey demands. C&C envisages using the USS 6300 to support or replace the traditional hydrographic survey launch. These conventionally-shaped vessels, with their hull-mounted sonar, are typically around 30ft but are limited to waves of around 0.5–1m which can restrict their application. “A boat has a relatively large waterplane – the projected area of hull lying in contact with the water relative to its displacement,” said Dan Hook, technical director of ASV. “As a wave passes across the boat, the buoyancy afforded by this large waterplane pushes the hull up and down. “At the other end of the spectrum would be a vessel with no waterplane at all – a submarine or conventional AUV. This allows it to work independently of waves but is limited in other ways. The USS 6300 ASV can be considered as a hybrid compromise between the two extremes, with the hull being submerged and only a tower or mast protruding through the surface. Because this has a much smaller waterplane, the vertical accelerations are of an order of magnitude smaller than the boat, which accounts for the greater stability. “The original SASS design featured
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Releasable nose-cone for launch and recovery
Multibeam sonar
Annotaded diagram of the unmanned semi
Attachment for the sidescan sonar transducers
submersible USS 6300
Lead-filled keel gives the vehicle stability Variable fuel space enough to give 4kts
a very high tower, balanced by a long keel,” said Dan Hook. “One of the design requirements demanded by C&C Technologies, however, was the ability to launch it from the back of a vessel in a similar way that it deploys its suite of Hugin AUVs. This meant a smaller keel section and similarly, a smaller tower section. “The sonar engineers at C&C had a very good fix on what motions were allowable and what weren’t. The design we developed together allows surveying in a maximum of 2m wave heights although it can survive in much greater sea states.”
for four days or 8kts for two days
Left: The more cruciform SASS. The lower keel is foreshortened in the USS 6300 Right: The USS6300 undergoing sea trials