the above posts are correct.
you didnt mention if you had a "no sell" agreement, but only that you could use the boat whenever you wanted....
whether you sell the boat to a friend, an enemy, or someone you have never met and will never see again, it makes no difference... the market can fluctuate to increase or decrease the value, or a hurricane could blow thru and total the boat completly, none of which you or the buyer has any control over..... (would you be willing to refund some of his purchase price if he were to take a loss on it, or help pay to fix it, if it became inoperable for some reason?)
only you know what the minimum dollar amount you have to get for the boat when you sell it, and if you sell it for that low dollar amount, dont feel bad if the new owner makes a profit on it.... this is the american way, and we ALL strive to be able to see our "toys" appreciate in value, no matter if we want to sell them or not.
unless a written signed contract is in hand, never, never expect the lip service given during a sale to mean anything at all, because it doesnt. sometimes people follow thru on their word alone, but dont
expect it, friend or otherwise..
how you deal with your friend afterwards may say more about you that this deal does about him....
when you sell anything, you release all control over it. and this statement is NOT hypothetical
..