As usual I agree with exactly what Wookie said. The Co-Ownership of a boat is very similar to a plane and the commercial aspects are probably very similar. In aviation in order to "collect" more than 49% of the cost you need to have a commercial license. If you are doing a Co-Owenership review the information in the link. You want to make sure that you have everything setup well so in the future you don't have any issues with other owners.
Co-Ownership: Navigating Airplane Partnerships | PlaneAndPilotMag.com
Co-Ownership: Navigating Airplane Partnerships | PlaneAndPilotMag.com