A water rudder will definately not solve that problem. Water rudders are for taxiing only. They should not be in the water when the plane is on the step. Water rudders that are in the water when on the step usually cause the problem you described.

If you are using Gee Bee floats, that is your problem. If not, it sounds like you have too much positive incidence in the wing. Make the top of the floats parallel to the bottom of the wing (That will give you about 1 1/2 degrees of positive incidence and that's plenty.)

Jim