catalinajack
Guru
Most folks? I don't think so, only those with, perhaps, smallish water tanks. Many boats have large or fairly large tanks. We did the Great Loop two years ago, not one Navy shower. We did shower efficiently but not miserly.
The propane heaters have an operational hassle. AS water is never unlimited mot folks will use the Navy shower system.
Wet down, soap up, then rinse the soap.
Usually the water is shut off while scrubbing and only turned back on to rinse.
The hassle is when there is no water flow the water heater burner shuts down , so the start of the rinse off is with cold water.
An ancient RV unit has a 6 or 10gallon tank , works fine , has 120v element for dockside.
A more modern RV unit has a tiny tank , but internal plumbing to keep the burner on.
Simple system is a funnel and hose leading to the FW tank.
The water can be left running so the temp is fine , at the cost of a bit of propane.