Sounds to me like you're making a monster out of a molehill. If you can live with the tendancy and compensate by an occasional paddle stroke correction, that would be the simplist cure.

A simple adjustable skeg would also be far easier then trying to determine the optimal correction angle and location with a calculator.

If you're really concerned with being able to optimize the correction angle for various boating conditions, use a rudder.

> After listening to lots of good advice about my kayak that has
> a tendency to pull to port, I have tentatively decided to put what
> some are calling a "trim tab" on starboard side. I definately
> have a very modest curve at end of boat which I can see in the bottom
> chine and which I think is rejplicated on sides of panels. I will
> also experiment this weekend with some foam to build up side that
> curves away from center, so as to resymetrize boat as Paul suggested.
> If I like the result I may turn this into a more permanent fix with
> real materials. For the meantime, I will proabably go with the trim
> tab on the side.

> This is my question. I suspect but do not know that water does
> not flow front to back under the hull of a kayak. If you just plop
> boat down into the water the displaced water would flow at a perpendicular
> angle to boats longitudinal axis - from midline to sides. I imagine
> that as speed increases the flow tends to straighten out but is never
> exactly front to back. The result of this for an off center fin that
> is under hull but not on midline would be that for any given speed
> there would be an angle of fin/skeg that would not apply corrective
> pressure because it would be in line with true direction of water
> flow. Conversely, a fin that ran parallel to boats direction of travel
> would have greater pressure on inboard side of fin and this would
> try and turn boat even though fin was straight. The least amount of
> drag would be at some angle to centerline, with the exact angle depending
> on the boats velocity. For best effect (least drag, most corrective
> action), I wonder if skeg should be angled for maximum performance
> at a specific speed (like 3 knots). On another list, I was also informed
> that current designs on sailboats and so on have an endplate at bottom
> of rudder or what have you to increase efficiency, presumably because
> this prevents water from "cheating" by sliding under rudder
> from the high pressure to the low pressure side. This simple idea
> adding a trim tab is getting complicated, although perhaps the impact
> of all these variables is negligible in reality.

> Dave