It is apparent that this method of conducting breaking wave tests on model boats is a useful and economical technique. Breaking waves were created which capsized the 36-inch model with as much violence and severity as that experienced by the boats in the 1979 Fastnet Race. Definitive records of the capsize dynamics were obtained on movie film. The weakness of this kind of testing is the f act that the boat and drogue are not riding on large regular waves prior to the breaking wave strike. Thus the amount of slack in the drogue towline may not represent a true storm situation.
The tests clearly showed that a drogue deployed from the stern can pull the boat through the breaking wave crest without capsize. However, if the towline has excessive slack at time of the wave strike, the boat can be capsized before the drogue pulls. The computer simulation of a boat/drogue system riding regular waves indicates that the towline should have little slack at the time of wave strike. It would be desirable to conduct model tests under natural wave conditions to confirm this analysis.
A very important observation emerging from these tests and the tests of reference 1 is that in a severe breaking wave strike, the boat can be brought up to wave speed before the load builds up in the drogue towline. This fact provides a "worst case" situation which in combination with a simple computer simulation, can be used to predict a maximum design load for any specific boat, drogue and wave combination. Using this concept, we can calculate that a 30-foot boat trailing a 4-foot diameter drogue could experience a maximum' drogue load of 7800 lbs. if struck by a breaking wave with a wave length of 300 feet and a crest velocity of 39 ft/sec. This "worst case" load estimate applies to relatively small boats, perhaps under 15,000 lbs. displacement, where the mass of the boat is small compared to the mass of the water in the breaking wave crest. For boats with higher displacement it is reasonable to assume that the acceleration caused by the breaking wave strike will be less and thus the relative drogue load should be smaller.
The tests described in this section provide an initial basis for the design of a full-scale drogue system for sailing yachts and other small vessels. Further model tests in natural waves would be useful.