Re: Weather Cocking Thoug

Posted by Laszlo on Jul 29, 2006

Weathercocking per se has nothing to do with the shape of the bottom. It's caused only by the displacement between the center of gravity and the center of effort. CG is where the boat's weight balances, CE is where the boat's sail area balances. For kayaks, "sail" is anything above the waterline that the wind can blow on.

If the CE is aft of the CG, the boat will turn into the wind. CE forward of the CG, the boat will turn away from the wind. Both in same position, the boat won't care about the wind. The greater the distance between the CG and CE, the more the boat will want to turn.

You can control the amount and direction of the turning simply by changing the direction and amount of the displacement.

So in an ideal world, if you're weathercocking and don't want to, you can move some weight around the boat and it will stop. I actually do this in my flat-bottomed, undecked pirogue. Going into the wind, I put my lunch & anchor up front. Away from the wind, in back. When it's really gusty (the way it was at Okoumefest, I sit in the exact center of the boat and lean back and forth to compensate for the gusts.

Underwater lateral plane area, such as skegs, keels, rudders and the shape of the hull, can fight weathercocking by generating a counterforce caused by the displacement between the center of gravity and the center of lateral plane. Same deal below the waterline as above, except that one set of forces is caused by moving air, the other by moving water.

Underwater lateral planes have the advantage of working without you having to think about it, but they may add weight and wetted area, increase required depth and catch on weeds. Active control of the CG/CE displacement doesn't do any of that, but it may be difficult in a decked boat.

The most efficient thing is to reduce sail area above the waterline to a minimum. That's why performance kayaks have cutdown flat rear decks. Of course, the biggest thing sticking into the airstream is the kayaker, but if the kayaker is sitting at the CG, they will make a negligible contribution to weathercocking.


In Response to: Weather Cocking Thoughts by Mac on Jul 29, 2006



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