The JSD is designed to keep the boat from being damaged by breaking waves. It allows the boat to move a bit, but doesn't hold it in place like a sea anchor does, which makes the boat a big target.
From the JSD website:
Contest 40, 250 mi. N. W. of Bermuda. "
Gusts were furious now. The seas were 25 ft with faces at 45 degrees and breaking crests. Deployed drogue. Slowing effect was phenomenal. Deploying the drogue was like jumping off a 30 ft. wave with a 40 ft. yacht. The feeling of being elastically tied to the sea itself is hard to imagine. We slowed to 1.5 knots with the stern pointed aggressively into the sea. It was as though we had entered a calm harbor of refuge. With the reduction in the yachts motion our situation seemed to be not too bad. We were exhausted and took the opportunity to get some sleep".
Many skippers have commented on the bungee type feel to the boats motion with the drogue deployed. This important characteristic was developed from model testing in the U.S. Coast Guards flow channel, which has glass walls so the underwater motion of drogue models could be observed. In a major storm, a yacht moves forward as it passes over the crest and backward in the trough for a distance of 50 ft. or more. The length of the drogue and the weight at the end is designed so that the drogue normally assumes a hook shape with the weighted end hanging almost vertical. When the boat is passing over the crest the drogue tends to straighten out and more of the cones take up the load thus checking the boat. In the trough, the weight sinks, taking up the unwanted slack in the towline. Thus the drogue is always aligned to respond to a dangerous breaking wave strike. The cones are attached at both ends so they cannot turn inside out if moving backward.
Model tests clearly show that the behavior of a parachute or cone drag device is unacceptable. As the device is pulled forward, it forms a wake behind it. When the towline goes slack the water in the wake continues to move forward and turns the chute or cone inside out, often causing it to tumble or foul the shroud lines. In the Coast Guard full scale tests in breaking waves on the Columbia River bar, the series drogue performed flawlessly and was retrieved with no damage, while a cone type drogue was destroyed.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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