The ultimate proof of the drogue is, of course, using it in actual breaking sea conditions. Finding personnel, vessels, and instrumentation able to withstand the severe testing environment is neither safe nor practical. Nevertheless, it was desired to test in as large a sea condition as possible while maintaining a reasonable amount of control. The Coast Guard's National Motor Lifeboat (NLMB) School in Ilwaco, Washington, was considered one such place where a full-scale test could be conducted. The school is located at the mouth of the Columbia River and has a substantial sand bar running across the entrance, forming an area of significant surf. Because of the experience of the personnel at the NMLB School and the availability of their 44-foot motor lifeboats, it was decided to conduct our tests there.
Our test instrumentation consisted of a load cell capable of handling 10,000 lbs, a knotmeter to measure actual drogue speed through the water, a tape recorder, and both series and cone drogues. We tested in 12-14 foot waves with a 2-3 knot current. Some of the waves had breaking crests.
The water depth was 20-40 feet. This, obviously, did not represent deep ocean conditions. The shallow water influenced the actual drogue behaviour in that under normal operating conditions the free end of the series drogue would have a 30-35 lb. weight attached. This allows all the drogue elements to lay fully underwater. For these tests it was not possible to weight the drogue sufficiently to keep all the elements underwater. During large pulls, the first 10 elements were pulled out of the water. This caused some secondary jerking on the load cell following the passing of a wave.
The results from the NMLB School testing were another verification of the use of a series drogue vs. a conventional type. The series drogue developed a maximum pull of 2500 lbs. Under the same conditions the cone drogue developed 2000 lbs. maximum pull. The boat rode better with the series drogue; there was not as large and sudden a jerk on the boat as it was pulled through the wave. Also, even though the cone drogue was deployed in the same wave conditions and was used for about 20 minutes less than the series drogue, it was destroyed at the end of the test. The cone had turned inside-out and one of the longitudinal seams was completely torn.
The only problem noted with the series drogue is that it was difficult to retrieve at the end of the test. Under actual storm conditions, it is most likely that the drogue will be used through the entire storm and not pulled in until the waves and wind have subsided. During this test we were pulling against the waves. Also, it should be possible on many, if not most, larger sailing yachts to run the drogue through an aft winch which would make retrieval easier after the storm had passed.
Despite the fact that the test boat was heavier than what the drogues were designed for, they were held stern-to the waves. These tests, along with the previously described work, have shown the use of a stern-deployed drogue is a viable technique for stabilizing yachts in breaking seas.