Okay, ofcourse doing muscles exercises, especially round the pelvis, are good, even very good. In Chi Kung the pelvis and the belly are the centre of all (the "tandien").

But sailing and catsailing in particular require dynamic action of your body. So the coordination of these enforced muscle groups is even important as the strenght itself. You don't want to end up as a weightlifter who cannot move swiftly anymore.
That's why I emphasized on trapezing on bumpy waters.

(And be assured that only a fool like me waste his fully trained body too much in any sport he does)