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warship, models exhibited unacceptable dynamic roll characteristics. With a shorter roll period, equivalent to that of a scaled mono-hull, this characteristic improved. Exploration of this phenom- ena during the trials of RV TRITON is a vital part of trimaran development. Tight control of the predicted roll period of the vessel was included in the specification. The contract for the design and build of RV Triton was placed with Vosper Thornycroft in July 1998 as the result of a competitive tender process. The ship was launched in May 2000 and deliv- ered to QinetiQ (then DERA) in August of the same year. Hull Form The main hull is of round bilge form with underwater sections approaching semi-circularity amidships. A gentle rise of buttock lines aft leads to a counter-stern transom with minimal immersion. The sidehulls are of multi- chine design on the outboard face with a plane inboard face for ease of manufac- ture. A parallel section is included extending above and below the waterline to avoid large changes in waterplane as displacement varies. Above this there is a flared section outboard and a haunch inboard to provide additional buoyancy as the opposite side hull emerges when heeling. Both hull and decks are longitu- dinally stiffened and supported by trans- verse frames at 1,500 mm spacing. Frames are fabricated up to two-deck level while above this both frames and deck beams are flanged. The steel grade used has a yield stress of 265 Mpa that is similar to the main structural steel used on frigates. Propulsion RV Triton is a diesel electric ship with both propulsive and ship service power provided by a pair of diesel generators. Drive is provided by a single conven- tional shaftline in the main hull, plus a right angle drive thruster in each side hull. The main shaft is driven by a single 3.5MW AC electric motor through a reduction gearbox. Side hull thrusters are driven by 350 kW electric motors. The prime movers are two Paxman 12VP185 powered 2MW diesel genera- tors backed up by a 400 kW harbour set and an 80 kW emergency set. A single fixed pitch propeller and rud- der are conventionally arranged under the aft end of the main hull. The capa- bility to fit a larger permanent magnet motor of up to 5 MW power has also been provided so that any related trials could contribute to the business case. Sea Trials Summary Report Since delivery to QinetiQ in August 2000, RV Triton has been conducting sea trials for the UK Ministry of Defence and the US Department of Defense to evaluate the performance of September, 2002 the trimaran hullform in various opera- tional scenarios and environmental con- ditions. All the trials were carried out under a Memorandum of Understanding between the two governments. These tri- als completed in March 2002. These trials were conducted in various sea states and at different speeds to ensure the ship encountered a diverse set of sea conditions. One of the perceived advantages of the trimaran hullform is the decrease in resistance and the lower power required to drive the ship when compared against the equivalent dis- placement monohull. In trials this has been proved as a reduction at high speed. RV Triton has good directional stabili- ty due to its long centre hull and the sea Navy trials have proved that she is far more comfortable in higher sea states than a monohull. Towing operations were con- ducted in one sea state higher than had previously been conducted for ships of RV Triton's size. 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