How big a boat?

An engine from a T-bird might just do. All it needs is a trip through
the car wash to get the oil and crud out of it. No big deal.

I used a truck engine to moor my SC22 for years, and the local marina
guy dropped a concrete mooring he cast in his own yard into my
beachfront for 250 bucks, delivered. He told me it needed to cure on
land for a couple of weeks to satisfy the enviromaniacs.

Terry K