I did the same thing and I know what your talking about. (my boat was the Malubu at walmart) I had the same proplem. I experimented a few times needless to say the best working thing I came up with was a new hull. When I did it I refused a new hull I wasted usefull time of my life. I finally made a balsa wood catamaran and It never turned to one side again. :-) But If you insist on the same hull try other things mabye you'll get lucky!

Electrolight