You draw up and agreement and you both sign. It only works because you both agree to make it work. The agreement needs to spell out all the issues (as in everything you can spell). If it is complete then it should be most fair. That is until someone becomes unhappy and then the partnership
fails. If both parties are not satisfied then the whole thing crumbles. If you are adding a partner and you want a 50/50 split then it really is important that you make sure you can come to a good understanding before you enter into the agreement. If you don't want to split the deal 50/50 then it will be difficult to maintain any partnership
agreement where you call all the shots and they get what ever you decide you want to give. Something like that screw the whole deal down the road.
Critical issues would include division of expenses, labor, boat use, and responsibilities. It would be wise to have a good insurance
policy as the accident
of one impacts the other. This would be a time for good insurance
coverage. making an agreement that outlines responsibilities is not enough when things go bad.
I know one friend in partnership with a boat and the deal works but they don't always turn out that way.