at constant speed; therefore deceleration could not be quantified. However, comparison of the results was quite revealing. While momentary resistance when transiting through a wave was indeed higher for the wave piercing hull than for conventional hull moving over the wave, by the average 22% in Sea State 4 and 28% in Sea State 6, the cumulative amount of energy over time, computed for the full cycle of the wave spectra, demonstrated that the wave piercing bow hull used only around 80% of energy of that of a conventional hull, which had extra resistance recorded while slamming and diving into incoming waves. What could not
be quantified,
unfortunately, was the effect of the observed stern emergence, prevalent in the conventional hull and nearly absent (zero incidents in Sea State 4 and two in Sea State 6 over the cycle of 50 wave crests) in the wave piercing hull. Tis suggests the difference would be greater if one assumes that a conventional hull would decelerate when propellers emerge, and would have to accelerate again to full speed. Also for the first time, the difference in motions at zero speed were observed, which is of particular importance for vessels operating in dynamic positioning (DP) mode, demonstrated that the wave piercing bow reduced motions, albeit less so than at higher speeds, which in this case were around 70% of those of a conventional hull.
Interest from ABS The results of this phase attracted attention of classification society ABS who were interested in the potential for reducing structural loads in the bow area, and resultant scantlings reduction. One year later under a co-operation agreement with ABS the final phase of research in the towing tank was carried out. Tis time, the model was self-propelled
and fitted, upon request of ABS, with seven pressure sensors (on one side of the hull) both below and above the wave piercing wing. Again, the model was tested in Sea States 0, 2, 4 and 6, and this time, the hull modified based on the results of the previous tests, demonstrated zero incidence of slamming. A new phenomenon was observed, which may have contributed to that, and which
Warship Technology October 2014 45
55M naval vessel design concept
certainly contributed to accelerations (at the bow, amidships and at the stern) being further reduced to only around 25% of the values measured on a conventional benchmark monohull at the earlier phases of testing. Pitch amplitude was not reduced any
further staying at about 45% of the values recorded on a conventional hull. However, it was observed that at higher speeds, around 25knots and higher, the wave piercing wings, by supressing the bow wave, generated a fix of water, spray and air under them, which seemed to produce additional cushioning effect. Te pressures measured on the bow below and above wave piercing wing were reviewed by ABS and found to be significantly lower than the values assumed for this type and size of hull in the High Speed Craſt Code rules. As the result, a letter was issued stating that in principle in this new type of vessel the scantlings in the bow area are permitted to be reduced by 15%, subject to separate review. A valid allegation of the research programme up to that point was that all
testing was limited to head and following seas, for obvious reasons in a towing tank. Tat led to the final phase of testing, which involved converting the last 3m-long model into a self-propelled (with four propellers as opposed to two tested in the basin), weather proofed, radio controlled technology demonstrator. Te logistics prevented the scope of testing originally wished for and the model was not instrumented, although fitted with a video camera in the wheelhouse. Several runs in the open waters of English Bay, in British Columbia, demonstrated motions in oblique seas not very different from head and following seas, leading the designers to believe wave-piercing bow technology is viable. Te most recent design was tested in
October 2013, with and without retrofit of canard wings on a hull of a 73m reefer with service speed of 14knots, under construction, to operate between Seattle, WA and Western Alaska. Model tests carried out in Copenhagen demonstrated reduction in motions in Sea State 5 and reduction of incidents of slamming by 75%.
The SHARC wave piercing bow
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