What is "form resistance"?

Question

What is "form resistance"?

Answer 1

The results of an experimental study of the resistance reduction from modification of the pressure field around displacement hulls creating fore-aft pressure re-distribution are presented. The fore-aft pressure re-distribution is achieved by hull surface porosity created by orifices through the hull which are connected to each other by fore-aft ducting. This affects the fore-aft pressure gradient when moving. Tests were completed with Model A, which has parabolic shaped waterlines, wall sides, a flat bottom and no parallel midbody. Resistance and surface pressure measurements were obtained with and without the pressure re-distribution orifices. The extent of pressure re-distribution was varied by using three ducting sizes. The resistance measurements and surface pressure data show that in some cases there is a large fore-aft surface pressure gradient and the fore-aft pressure re-distribution results in a significant reduction in the vessel resistance. The test results suggest that fore-aft pressure re-distribution may have benefit in reducing displacement hull and/or SWATH strut resistance.