The detail below was provided to us by the late Don Jordan, who supported and encouraged our efforts to build series drogues.
Research and Development Program — Don Jordan
With the data from the 1979 Fastnet Race in hand, I started by making scale models of some of the boats in the race and testing these models in natural waves and man-made waves. It is a fortunate fact that small waves behave like large waves and small models behave like full scale yachts if some simple dynamic similarity rules are observed in the model design and testing. I had no preconceived ideas on what these tests would reveal.
At the same time, extensive tests were being conducted in the U.S. and Europe to determine whether the Fastnet tragedy was caused by the design features of modern yachts compared to traditional designs. ” Killer Yachts” they were termed by some leading naval architects. After much effort, it was concluded that there was no significant difference in the capsize vulnerability of modern yachts or traditional designs. I repeated these tests and got the same results. The Fastnet disaster was caused by the severity of the storm, not the boat design or the tactics of the skippers.
I then undertook a program of basic research and development to understand and find a solution to the storm survival problem. In this effort I was greatly assisted by the U.S. Coast Guard, who made all their applicable facilities available for my use, and finally tested the series drogue in breaking waves at their motor lifeboat test site. The program, which continued for four years, led to the following general conclusions:
1. To protect a yacht in a hurricane, an outside force must be applied from a drag device.
No design changes to the boat and no storm tactics on the part of the skipper can result in a significant reduction in risk.
2. The drag device must be a drogue, i.e. the boat must be tethered from the stern.
(I have found this to be the most difficult concept to get across)
3. A sea anchor cannot be designed to protect the boat. When tethered from the bow, the boat will yaw and develop unacceptable loads. The reason for this is that all boats must be designed to be directionally stable when moving forward – or it would not be possible to steer the boat. Therefore, if moving backwards, the boat will be unstable and will yaw and turn broadside to the sea.
4. The drogue must consist of multiple drag elements strung out along the tow line. A single drag device of any size or shape will not provide protection.
5. The drogue must be designed so that a significant number of the drag elements are deeply submerged and do not lie on the surface.
6. The design of the multiple design elements must be such that, in a “worst case” breaking wave strike, peak transient load will not exceed the design value for the drogue components or the boat attachments.
7. The strength of the drogue and the number of drag elements must be adjusted to be compatible with the displacement of the specific yacht.
8. With a proper drogue, a yacht and crew can survive a storm of the severity of the Fastnet or 1998 Sydney-Hobart storm with no serious storm damage or crew injuries.
I am an old aircraft engineer. In the design of aircraft, certain machinery and equipment is in a separate category, “safety of flight”. These items must be absolutely reliable and must be capable or enduring the worst environment that the aircraft may encounter. The series drogue is designed to this strict safety standard. None of the other various drogue and sea anchor types can meet this requirement.
However, there is only a very small chance that any one drogue will ever encounter a worst case-breaking wave. I have made a strong effort to prevent any compromise or substitution, which might reduce the size, weight or cost of the drogue but might compromise the safety.
All series drogues are built to a rigorous specification various skippers have proposed ways to “simplify” or reduce the cost of the drogue – such as using 3 strand line or using larger and fewer cones. I have managed to hold the line so far – but I have no control over individual builders.