tack and speed differential

[balthazor]

<div>My July cruise up north confirms that my 382 seems to do at
least a knot more on the starboard tack, a knot less on the
port, especially close hauled. The rig looks equal on each in
terms of sag, bend, etc. The problem is surely not the knot
meter, which is virtually centerline. And, anyway, I can feel
the difference. At the same time, the weather helm is greater
on the starboard tack, as we go faster. Any suggestions or
comments? thanks.
</div>

 

[bschnur]

Terry,
The next time your boat is hauled, take a very close look at the rudder. Sight from the aft edge, looking forward, and compare the amount of curve on each side of the rudder. You may find that the rudder is essentially flat on one side, yet is well curved on the other. I've heard from others on this board that they found the same condition on their stock rudder. I discovered this problem while enlarging my stock rudder, so I was also able to correct the shape at the same time.
If your rudder has the same problem, this could easily cause extra drag on the opposite tack. Said another way, because of the difference in shape between the port and stbd sides of the rudder, one tack will require considerably more helm to hold the same relative angle while pointing, and this translates to more drag and slower speed on one tack.
I'm sure that there are several other possible causes, but this one is sneaky and you really have to look for it. Good luck.

 

[balthazor]

So, do I want my rudder to be flat sided or curved?

 

[bschnur]

You'll want identical curvature on both sides. The curve is like an airfoil, thicker at the front edge and tapering towards the rear edge. Also, while examinining the rudder, check to see that it's perpendicular to the long axis of the boat. Mine had a "kick" of about 3" to port in the lower third. I'm not sure what effect that had on handling, but it couldn't have been good.