A broker that I used to work with and bought and sold several boats through gave me an editable copy of the YBBA purchase and sale contract several years ago. The brokerage owner who was a former YBAA president had no qualms about providing that. So if you can find it, simply modify the agreement to remove all broker references and responsibilities and replace with what makes sense in a simple two party sale.

Also look on BoatUS' web site for advice on what to include in a contract. BoatUS used to have a sample contract as well as an escrow service, but alas I can't find it now.

David