Feature 3 | ADVANCED HULLFORMS


NaviForm believes there are numerous potential military and commercial applications of the wave piercer


does not represent the need to postpone programmes already under way, or even vessels already under construction. SWPM can be applied to every type of warship hull, designed to operate at any speed.


The research continues using CFD,


which enables testing a much wider range of forms of SWPM than physical testing in a towing tank. Further improvements are anticipated.


Military applications NaviForm believes that application of SWPM bow to military craft offers a number of potential advantages. First, it would provide a platform more stable in heavy weather than conventional monohulls or multihulls, size for size, allowing for improved weapon and sensor system and faster reaction and target acquisition. It would improve crew performance by reducing fatigue and incidents of seasickness. Unlike multihulls that are subject to wave impact against underside of the deck spanning the hulls, monohulls, especially fitted with SWPM bow, do not have their operation limited by wave height to the same extent. Second,


the SWPM bow has the


potential to increase top speed and reduce fuel consumption. In certain operating scenarios, warships cannot reduce speed as much as merchant ships do in heavy seas. Propeller emergence is a well-known and documented problem in warship operation, and research to date indicates that fitting a SWPM would greatly reduce its incidence. In turn, it would reduce the incidence of deceleration associated with propeller emergence and broaching, the need to accelerate back to speed and as the result, the average speed would increase and transit time would be reduced. Quite apart from operational considerations, it would also result in fuel savings, which is


46


increasingly important under the current budgetary constraints. A version of a wave piercing monohull


was considered for a proposal of the builders of US naval craſt in 2005, was extensively analysed for its impact on the vital hull signatures, notably noise and radar. It was determined that noise signature was reduced, as slamming was eliminated in the particular 66m-long hull under consideration at the time. Radar signature, initially found higher due to the concave shape of the SWPM bow, was


“The use of wave piercing bows on naval vessels is increasing”


successfully reduced to match that of a benchmark hull fitted with conventional hull, by using a series of flat surfaces rather than a single curved surface. Te hull size limitation for the application


of the SWPM is, for all practical purposes, only at the lower end. Experience with a range of hull lengths tested indicates that for hulls shorter than 30m a full version of the SWPM is not practical. It is noted that the retrofit of the canard wings will benefit any size of hull. SWPM does not have to change the layout of the hull, or even the shape of the bow. It can be retrofitted to existing hulls, or considered for hull whose design and procurement is already well advanced. Consideration of SWPM bow


Further applications Te company believes that application of SWPM on commercial vessels involves a much wider range of hull types than the original concept involving a high-speed crewboat would suggest. Reducing motions and eliminating slamming is obviously beneficial to any type of hull carrying passengers, crews to offshore installations, or cargo. Apart from improved economics of the operation, primarily in the form of fuel savings, improved crew and passenger comfort, and reduction in cargo damage are compelling. There are certain types of merchant vessels that would not benefit from SWPM application, either because their size alone prevents excessive pitching and slamming, or the nature of their operation precludes fitting appendages. However, NaviForm believes that ferries and roll-on, roll-off (ro-ro) ships in particular stand to benefit from fitting a SWPM. The first commercial vessels fitted with SWPM are three FSIVs built in Singapore in 2008-9, which are currently in service in the Gulf of Arabia. “It can be expected, as it was proven


in model testing and on the first three FSIVs, that motions in waves will be reduced,” said van Diepen. “Vessels fitted with SWPM will also benefit from lower fuel consumption by avoiding propeller emergence and decelerations. In ro-ro vessels SWPM can be integrated in such a way that the ro-ro decks can carry their full width farther forward than conventional ro-ro, which invariably features narrowing forward decks that operators cannot fully utilise.” As van Diepen noted, the use of wave


piercing bows on naval vessels is increasing and includes high profile projects such as the US Navy DDX 1000 destroyers, Axe bow offshore patrol vessels and naval versions of the high-speed catamarans. Tere are a number of different approaches to wave piercing design but the goals are the same – improving operability in high sea states with minimum degradation in speed. WT


Warship Technology October 2014


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