Here are some possible issues with sailing a Proa downwind. These are from a theoretical viewpoint
since I have never sailed a Proa.
When sailing downwind the heeling moment from the sail will be aligned in a fore and aft direction along the LW hull,
and will tend to bury the bow end of the LW hull. The righting moment (from the weight in the WW hull) is aligned
at right angles to the heeling moment, and thus will do nothing to counter it.
Also when sailing downwind the aerodynamic force will be positioned at the LW hull, while the majority of
the hydrodynamic force will be positioned at the WW hull (since this is where the weight is). This would
result in a large moment attempting turning the Proa into the wind. The rudder force needed to counter this would
add drag.
These issues would be in effect even when the apparent wind is directly on the beam.
A possible mitigating factor for a Proa is that they may sail fast enough for all courses to be close reached.
Gardner, thanks for putting your questions out there. I have learned a lot from your questions - and the answers.
Malcolm
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