IMO, I own the boat, the non boater is responsible for atleast 1/2 the cost. You have the boat payment, insurance, wear & tear, care, maitenance etc.
Thats not including the gas, oil.
I have had that happen to me before. I dropped a guy that tourney fished with me for this very reason. I let him slide once and he pulled the crap the second time. After that he wondered why I didnt want to fish with him anymore.
If it was me and you really like fishing with the guy I'd express my concerns and let the chips fall where they be.