Just a cautionary note: propane water heaters can be DEADLY on a boat. There are numerous instances of CO poisoning resulting in death from these devices.
See, e.g, the following:
Quote According to the U.S. Consumer Product Safety Commission, 164 CO-related non-fire deaths were attributed to heating and cooking equipment in 1994.** The specific types of equipment were:
* Gas-fueled space heaters (70 deaths)
* Gas-fueled furnaces (48 deaths)
* Charcoal grills (15 deaths)
* Gas-fueled ranges (9 deaths)
* Liquid-fueled heaters (9 deaths)
* Gas-fueled water heaters (7 deaths)
* Solid-fueled heaters (6 deaths)
Propane is nothing to fool with on a boat. Moreover, it's unnecessary since there are other less dangerous ways to provide hot water (electric HWH, engine-heated HW, etc.).
Sorry if this sounds gratuitous, but many folks just aren't aware of the dangers of gas hot water heaters on boats.