There should be a zinc anode very close to the prop - somewhere on the foot, in the
water. That should take care of it.
I'm reluctant to go with the wingnut answer. Wingnuts are finger tight, not properly torqued. Having a hydrofoil pull loose while on a plane could be spectacularly messy.
Are you having trouble getting up on a plane? Is that the problem you are trying to solve? If so, consider a finer (less pitch)
propeller. Think of prop
pitch as choosing a
gear - the finer the lower, the coarser the higher. Struggling to get up may be starting in too high a
gear. Hydrofoils help at the other end - more
lift - but the
price tag is more drag.