Rigging?

Is your mast in-column? That is to say: Is it straight up-and-down, from side-to-side, and straight? It sounds to me like it's not. Is the standing rigging appropriately tensioned? I would not be surprised to find it's not.

You might wish to read Giulietta's "Adjusting You Rig" how-to, which is sticky'd at the top of the Gear and Maintenance sub-forum. Also illuminating is Ivar Dedekam's Sail and Rig Tuning. I recommend obtaining a Loos Pro wire tension gauge. I think they're well worth the investment. But you can get by w/o one, if necessary.

Jim

Thanks for your post SEMIJim; I thought it probably had something to do with that.
Thanks also for pointing to that excellent post

JJ

If it's not the rigging, could be the fairing on the keel and/or rudder. More lift on one tack.

More Junk....

On one side. Example do you have a bunch of sails and if so are the all stacked on top of each other on one side? How about water tanks? If you have one on each side, is one filled more than the other? If you have 40 (2x20 gal tanks) gallons of water, and only on of the tanks is filled, that's an extra 160 lbs on one side. That might not seem like a lot, but that is the equivalent of a extra person on that side. Another easy way to tell if you have extra weight on one side versus the other is to take a float around your boat and look at the hull, does one side list a little more than the other? If so that could mean that side has more weight.

A good starting point, before you look at the rigging, is to see if you have an unbalanced load of stuff on one side of the boat, especially towards the bow. If so, redistribute and try again (sailing) and see if that helps. If it doesn't then look at the rigging.

DrB

Lots of possibilities here. There was a Tartan 37 in our harbor whose keel was built skewed off center. Hopefully your issue is with the rig, which can be fixed pretty easily.