Feature 7 | ADVANCED HULLFORMS
incorporated trunks in the catamaran hose sizes, may be somewhat more diffi cult. for tumblehome wave-piercing forms in
section. Th is allows a conventional exhaust However, systems can be connected aft er general, may become a limitation in severe
location with respect to the catamaran the hull is extended, and disconnected seas states, and further hydrodynamic
superstructure. However, it demands the prior to retracting. Personnel and material research and the development of
design of a watertight seal detail (at or near access arrangements presumably will appropriate analytic tools, as discussed
the level of the wet deck of the catamaran require a system of double watertight below, will be extremely helpful if this
section). These seals must be made hatches to trunks, with locations provided concept is to be further developed.
eff ective when the centre hull section is for use in the extended and retracted The hydrodynamic performance of
extended, and can then be ‘broken’ before hull positions. Details of these systems the adjustable-length trimaran was
disengaging the locks and retracting the have not been developed, but they are studied using three diff erent numerical
centre hull section. Th e development of considered feasible. techniques together with a large-model
seals for these arrangements is considered The adjustable-length trimaran is an test programme. Calm water resistance
challenging but feasible. interesting vehicle for the extremely was predicted using a code based on
Distributive systems and personnel access challenging HSSL speed, range, payload thin-ship theory and the CFD soft ware
to the centre hull present another peculiar and austere port access constraints. At FLUENT. Seakeeping motions were
challenge to the designer. Important systems least to the level of a concept design predicted using a program based on
that have to be able to connect the centre weight estimate, it meets the basic HSSL classical strip theory. The powering
hull and catamaran sections are electric mission requirements. In exchange for experiments tested the trimaran in six
power, fuel fi ll and transfer, and internal this, however, the concept presents several diff erent confi gurations of varying overall
communications, control and monitoring. unusual design challenges. length, beam, and draft . Th e seakeeping
The centre hull and catamaran sections Apart from primary structural loads model tests were done in a wide range of
can (and probably will) have independent and locking arrangements, which are sea states, heading angles, and two forward
ballast and bilge systems, fi re main, seawater obviously key areas for further analysis, speeds, with the model possessing the
cooling, and other auxiliary systems the low freeboard of the centre hull lowest-resistance, large-length, narrow-
such as lubrication oil, fi re extinguishing, (assuming stagger with the centre hull beam confi guration.
compressed air, and ventilation. forward) is a leading concern. While Th e adjustable-length trimaran geometry
Th ere are, however, sound reasons to wetness of the centre hull is not necessarily has sub-hulls that are located relatively
keep the electric generating plant entirely an intractable design issue, it will require closely to each other; these sub-hulls are
in the catamaran section. In this case, careful attention. heavily loaded, particularly upon departure.
electric power to the centre hull will have to Th e relatively small reserve buoyancy These attributes challenge the viscous
be transferred by internal ‘festoon’ or cable and breadth forward has been observed prediction that is used for calculating
and reel systems. Signal connections that (during model tests) to permit wave total drag with the thin-ship theory code.
must be hard-wired may also use a similar impacts to occur on the forward surfaces of Consequently, the viscous prediction was
festoon or cable and reel, or possibly some the cross structures. Also, asymmetric pitch sensitised to the closeness of the hulls by
wireless connections can be incorporated. responses (bow down peaks substantially estimating the increase in velocity realised
Fuel fi ll and transfer systems, due to large greater than bow up) of the kind noted by the inter-sub-hull fl uid.
Adjustable-length trimaran with aft stagger of the centre hull.
68 Warship Technology October 2008
WT_Oct08_p61+64+66+68+70.indd Sec4:68 10/10/08 1:20:28 PM
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