As a career captain, I have done this with several owners, and it has worked out well. But, this guy seems to be trying to take advantage of you. Obviously, your expenses are going to increase as well as wear and tear on the boat. Therefor, you are not in any position to "share" any expenses or costs. As a matter of fact even the captain's wages should be born by the chartering, when under charter, if he is pocketing anything beyond a commission for booking the charters.
If you want to try this, "rent" him the boat on charter days. Figure out what you will need to make to recoup the added insurance, maintenance and possible repairs; you will almost certainly not make a profit. That way he has all the legal responsibility with the CG and local LEO's. Have your lawyer draw up a bareboat charter contract (you can perhaps get one from a bb charter company?) Do not accept that this guy has any insurance coverage; that is YOUR responsibility. If you are paying him a monthly salary, then figure what the daily rate is and add that to the "rental" fee; no need to pay him twice.
You will have no way to check if he's being honest with you about the number of days he works, (especially if you do not live locally) but a record of engine hours may help. I would hope that this fellow is entirely trustworthy, but best to be cautious. Pm me if you'd like more info.
