I know two guys named John and Jon. No, really! They both have partners. Jon's partner, just to complicate matters, is also named John! Really, still!!!
Anyway, Jon's partner John didn't like doing any work on the boat and didn't want to pay for any upgrades. These included sails, new running rigging, a GPS, a heater, an inverter, you name it. So Jon bought it all, and John got the use of it. Eventually, Jon bought out John 'cuz John was getting too long in the tooth to enjoy the boat, but he got all sorts of improvements and this was a new 1998 boat. Guess it worked both ways and worked out, 'cuz even if Jon paid for all the toys, he got to use 'em, too, and now owns the boat. Wouldn't have worked out the other way though.
Now, the second John has had two different partners, and is perfectly happy. He does all the work on his boat and the other guy just sails it. He says it keeps his costs down, as he's retired. His deal is more of an ongoing "rental" thing that an outright half-purchase/share of the boat, IIRC. Maybe not. He lurks this board sometimes, maybe he'll chip in.
You could also do a simple search on this board under "boat partners" or "Partnerships" - I know it's been discussed before, some at length.
If it was me? I had a sailing buddy who had no investment in our boat, but he volunteered to help with everything, and did. I'm glad it's still "my" boat, though. That may be the best "partnership" ever!
'Cuz I didn't have to figure out the "end game" which is what you really should do up front. That flipping a coin can lead to hard feelings if both want to keep the boat. Why not simply continue the partnership?
"End game" and expenses and upgrades should be in writing. But:::is a GPS an upgrade? Lotsa different issues. Make a list or wing it.
Good luck.