Two types of waves were used for this test program; natural wind-driven waves formed on local bodies of water, and a continuous breaking wave formed by the wake of a power boat.
To test the 1/10 scale model in conditions simulating ocean storm waves driven by a 60 mph wind, it was necessary to select natural waves 3 feet high and a wind of 19 mph. It was not difficult to approximate these requirements in actual tests. Visually, 3-foot wind-driven waves appear to be generally similar in shape and behaviour to large wind-driven waves. The wind forces cause each wave to form a cusp-shaped crest which grows and steepens until it collapses forming a whitecap. As with the boat models, all the forces within the waves scale correctly except the viscous forces. It appears that viscous forces do not have a large effect on wind-driven wave shape at wave heights above 1 or 2 feet. The effect of Reynolds Number on wind-driven waves in this size range has not, to our knowledge, been studied in detail. For the purposes of this investigation it is believed that the scaled natural waves will provide useful information regarding full-scale experience.
The second type of wave used in this investigation is a breaking wave formed by the wake of a power boat. The size and wave crest momentum of the wave could be varied by changing the type of powerboat or the speed. A wave was chosen which would violently capsize the models when no drogue was used. Scaled to full size it would represent a breaking wave 20 to 30 feet high moving at a speed of 20 to 25 mph. The test wave had a large mass of moving water in the crest and thus represented a very dangerous configuration. At this time no information is available which would permit a more accurate simulation of a full-scale breaking storm wave. Perhaps the best that can be said is that the breaking wave used for the tests would capsize the models with as much and probably more violence as the Fastnet capsizings described by the crews of the affected yachts.