If you can prove you are half owner (which sounds like it may not be crystal clear since your name is not on the title), your friends creditors should have no rights to claim your half of the boat, just your friends half. Unless your buddy borrowed money and pledged the boat as collateral without telling you... possible since his name is on the title. This sounds like even if things end up working out for you, you will get tied up in bankruptcy proceedings. The creditors don't want a boat, they want cash, so an offer to buy the other half of the boat may be well received by both the court and creditors.
Definitely time for a lawyer. Start collecting all the documentation you can that would prove or at least support that you are indeed half owner.