David:
You might look into credit unions (they have some good programs) but be careful (they do not work the same as a bank, on the pay ahead thing = must make "at least one" payment every month) or pay it all off.
Best direction for you, is to get a loan (if you have OK credit and do a bit more research) you may come up with a winner ! also documented vessels may be a bit easier to get a loan on.
In any case
Best of luck
Oh David: If you are Disabled (I am not sure you know what you are getting into, sailing can be a handful) but if it is a mental impairment, you should fit right in. Within the sailing community, most are pretty open minded and do march to their own drum.
Lastly: if you think you can pay 1.6K for a 40K Boat and sail off to (Tonga or ?) here is hoping that the seller is a little wiser than that.