Verbal contracts are enforceable
It is always better to have written contracts. The Statute of Frauds (has nothing to do with fraud) states that certain contracts MUST be written; such as for the sale of real property; leases greater than one year; a person agreeing to pay the debt of another; and something else to do with being the executor of an estate. You could sue the individual and have a decent chance of winning. You have the 1/2 insurance payment documentation as well as your check to the previous boat owner to help establish an interest in the boat. If you can provide a witness to the verbal contract, that should be a clincher. If the current "owner" is truly a friend he should wish to settle the matter out of court. If you get a judgment against him, that could cause damage to his credit scores, and hurt him more in the long run. I hope your friend listens to reason. Life is just too short to spend it on unpleasant matters.