Feature 3 | ADVANCED HULLFORMS


commercial client, both models were tested in Sea States 4 and 6. The wave piercing bow has evolved


Evolved hullform from wave piercing crewboat showing how the bow form evolved from wedge with deflector added


concept was the only one that could meet all the requirements; however, the vessels were never built. It was noted in the operator’s final analysis that one of the main reasons the SWPM was selected was its ability to physically accommodate the size of the power plant necessary to achieve the specified speed. Te proposed tri- and catamaran hulls were too narrow to accommodate this. In the following years, a partnership was


formed with the National Research Council Canada and American Bureau of Shipping (ABS) to embark on a systematic research with the objective of developing and optimising a monohull that would result in reduced motions in waves. A total of six separate research projects were undertaken, all involving model testing at the total cost approaching US$1 million, spanning 10 years, from 2000 to 2010. Te result of this research programme


not only met the objective of reducing motions (vertical accelerations and pitch amplitude) by 25% but exceeded this goal by the factor of two. Several other phenomena were identified that were not initially anticipated, and that has resulted in a further enhancement of the platform in terms of motions, speed, reduced construction and operating costs. Te initial phase of research involved


the type of bow originally proposed for the military concept craft, testing the new type of hybrid propeller and waterjet propulsion. In that research, general motions and accelerations were not as


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much a concern as the ability to keep propellers in the water in all weather conditions. Te navy’s objective was to develop a hull that would minimise the incidence of propeller emergence and hull deceleration. In testing, prior to year 2000, the type of bow that fulfilled those objective was wedge shaped and it reduced incidence of stern emergence by keeping the bow down, moving through waves. Such wedge-shaped bow was therefore


selected as the starting point for the systematic research programme, the first phase involving model testing in a local small 70m model basin, involving a model with two interchangeable bows, one conventional and one wedge shaped. The wedge-shaped bow did indeed


prove superior in reducing pitch amplitude, accelerations (measured at three points along the hull) and observable incidence of slamming. However, it also demonstrated excessive wetness on deck which was recognised as not practical for fully functional vessel operations taking into account safety of crew and the topside equipment. Mitigating that effect was the subject of the following phases of research.


Conventional vs wave piercing A much expanded scope of testing programme followed in a large model test facility in Newfoundland, Canada. Tis time, two hulls were tested in the same conditions, one wave piercing and one conventional, in an array of wave spectra and amplitudes. Mindful of the recent requirements of the


from a wedge, into a set of wings which uses inverted NACA profile to generate vertical force which prevented the bow from liſting in waves and from initiating pitching motion. Te bow was now fitted with a wave deflector designed to protect the deckhouse and the topside equipment. Te results were even more encouraging. A marked reduction of motions and accelerations in Sea State 4, with topsides dry, with admittedly impressive magnitude of the spray generated by wave deflector. But the wheelhouse remained dry. In Sea State 6 the difference in response of both models was far more pronounced. At wave height of 6m, the wave piercing hull would still not slam, the stern would not emerge, and it would either ride the long waves in the spectrum, or move through the short ones.


Conventional hull The conventional hull model test gave credence to operational limits imposed by authorities in the operation of crew boats at Sea State 4. Te hull not only would emerge from waves and dive into another incoming wave, water exploding against the front of the wheelhouse, it actually physically broke off the carriage on two occasions until the test facility refused to continue testing that particular model in Sea State 6. Te video footage was edited to match the


wave spectra for both hulls and combining one model runs above another, so that both could be viewed, at speed scaled down to full-scale speed, simultaneously. Tis was done for speeds up to 20knots in Sea State 6, as above that speed the conventional hull suffered physical damage and could no longer be tested. It is also noteworthy that this round of testing addressed a recurring question about resistance increase while moving the hull through the waves as compared to a conventional hull moving over the wave. That question was prompted by the


observed magnitude of spray thrown by the wave piercing bow and its wave deflector, seemingly larger than that for a conventional hull. Resistance was measured on both hulls, for all runs. Te models were not self-propelled, but towed


Warship Technology October 2014


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