Eric, it can be like brokering a 4-way marriage. Dog or cat? Apartment or House? Minivan or sedan? Steak or chicken?
If you cna figure out a way for everyone to come into it with their heads in the same place, same expectations, full and unreserved agreement to a set of partnership papers drawn up by an attorney...it might work. The LLC is a good idea and in order to get insurance, you may need to get commercial ($$) insurance if a corporation or LLC owns the boat. Ask your broker what's possible! Remember, one day someone will need to leave the partnership, so your papers also need to consider a voluntary sale, a forced sale, a dissolution, how to get money if someone files bankruptcy but the boat needs repairs...What if one partner says "I'm out, here's my replacement" and you don't like the replacement he's already sold out to?
It works very nicely for some folks, very casually for some folks, but scares the heck out of those who might get caught up in a "bad marriage" that way.