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What JH said.
Depending on the frequency of the wave train, a mast-intact boat may have a better reaction to that frequency that a mastless boat. Having anchored beam-to a small swell, I can attest that there isn't a lot of roll dampening in modern sailboats. Otherwise we wouldn't care or notice the defference much.
Note that the wave train frequency that sets up roll oscillations would be limited to some very specific frequencies. At the dock, jump off the side of your boat and time how long the side of the boat takes to go down and back up again (start the timer when the side of the boat is at its highest). For more accuracy, time over several cycles and divide the time by the number of cycles. The answer you get is the same as the wave train frequency that will set-up the worst roll oscillations of your mast-intact boat. (Actually, harmonics of that frequency would likely have a similar effect, e.g. a wavetrain frequency that was a third of what you measured.)
With your mast gone, the boat will have a higher roll oscillation frequency, and would react to a different wave train frequency, perhaps the one currently facing your just-dismasted boat.
If anyone who is taking their stick down wants to do this test before-and-after, it would be a great YouTube video.
P.S. Of course, if you have forward movement, you could change your heading to alter the apparent wave train frequency. If hove-to with a sea anchor, changing to a smaller/larger sea anchor -- to add/subtract downwind drift speed -- could theoretically affect the apparent frequency, conceivably enough to matter. Perhaps a better and easier tact would be to let the sea achor act as a roll dampener by running some of it's (characteristically dampening) force to an off-centerline cleat, via a snatch block on the sea anchor line.
P.P.S. Theoretically, when not moving, altering the angle of the boat to the waves doesn't fully alleviate the runaway roll problem, since the underlying wave train has the same frequency, if not the same strength-per-individual-cycle. This is why people buy rocker-stoppers and other roll dampeners.
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Last edited by Bene505; 03-01-2012 at 11:33 AM.