Micha,
I caught the yaw issue, but having the separation wider (fore/aft) than the beams didn't cross my mind. I guess I assumed that some boats having it on the beams was good enough. As it is... my beams are only 24' (out of 60') apart. So, I'd have the issues you're describing. So either I have to have all that appendage down the hull with the resulting loads through the hull and trailering issues, or I have to splay the beams. Too many things were relying on the beams being parallel. This will take some serious head scratching.
Thanks,
Dennis
From: Micha Niskin <micha.niskin@
To: harryproa@yahoogrou
Sent: Wed, July 28, 2010 6:52:46 PM
Subject: Re: [harryproa] Re: 60' Trailerable Proa
STEERING MOMENT. You also might want rudders on the leeward hull in order to enhance steerage. When Blind Date went from the standard rudders on the leeward hull, to beam-mounted rudders, it started rounding up into the wind. Just a meter or two on each end can be enough to go from laminar flow to turbulent flow, and that makes all the difference. The further apart those rudders are, the less rudder you'll need at speed in order to maintain a course.
Drag on rudders positioned to windward of the yaw axis could also result in the rounding-up moment you observed. This effect would be worse the farther to windward they are. The same effect (with an opposite sign, of course) would be observed for leeward-positioned rudders.
Micha
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