When I'm driving my '89 at idle speeds the steering wheel turns very easily, I can spin it lock-to-lock with one finger, there's no perceptible drag, no obvious problems. However, once on plane, turning the boat becomes a chore. Anything more than just a slight correction is definitely a two-hand job, it takes a fair amount of strength and concentration to do it. This makes me think the rudder is binding when under load, and not necessarily a steering cable problem.
Any advice as to how to go about looking into this? Does the rudder have a bearing that needs to be lubed/replaced?