I found a answer:
Boat vs RV systems
Many, but not all, systems aboard a power boat are similar or identical to the systems aboard a motorhome and a subset are similar to the systems found on other RVs. As a result, I’ve been able to apply much of my systems experiences and learning interchangeably between the two. The following comparisons are by no means comprehensive, just the items that I think of as I write; I’ll add to them as more come to mind.
Some examples of similar or identical systems are:
* Fresh water system, including fresh water tank, pump(s), plumbing and filter(s).
* Electric water heater (most boats don’t have propane water heaters due to the explosion risk with LPG leaks).
* Shore power, except that some marine hookups use different plugs and 50A marina comes in two flavors for a boat.
* Basic engine, but a boat may have one or two engines. (I’m ignoring I/O or outboard engines for the purpose of this discussion.)
* Power steering.
* Starting batteries.
* Emergency start/crossover.
* House batteries.
* Inverter batteries.
* Battery disconnect switches.
* DC lights.
* AC lights.
* AC receptacles and GFIs.
* Kitchen/galley extration fans.
* Navigation system (PC-based, stand-alone, or handheld), but road/street maps are replaced with navigation charts.
* Electric stove.
* Microwave or micro/convection oven.
* Fire extinguishers.
* Fiberglass/gel coat. Few recreational boats have the equivalent of ‘full body paint’ used on many RVs.
Examples of systems that are usually quite different in a boat are:
* Engine cooling will be either sea water directly or sea water cooling via a heat exchanger. (The latter is often referred to as “fresh water cooling”, but usually uses coolant similar to road vehicles). Either one requires a sea water pump.
* Similarly for generator cooling.
* The transmission will be a simple forward/neutral/reverse.
* Propulsion is eiher by propeller(s) or jet pump(s). Some layouts require V-drives. Tires and wheels bearing issues are replaced by a host of others.
* Preventing or minimizing sea water leakage around through the hull where the prop shaft(s) enter.
* Steering is from the rear, by rudder (except in the case of jet drives). Some power boats also have bow &/or stern thrusters to provide manouverability in close quarters.
* No suspension components to worry about.
* No brakes or ABS to wear out or fail.
* Communications usually VHF for inlland or near-shore cruising. Cell phone coverage is often adequate.
* Air conditionning and heating use reversible heat pumps fed by sea water to transport heat into or out of the heating/cooling unit.
* Toilet flush is typically vacuum flush with some water added. This is also being used on some RVs to allow “remote” location of the black water tank.
* Grey water is either discharged directly overboard or drains to a sump and pumped overboard from there.
* Black water is either pumped directly into a holding tank, or via an on-board treatment system. Rules for overboard discharge of treated sewage varies, but is allowed in some inland waters. No discharge of untreated allowed unless outside the 3-mile limit. Emptying a black tank usually requires involves a pump, either on board or dockside.
* Below-water through-hull fittings are something the typical RVer doesn’t need to worry about. For the boater, a failed or leaking fitting could result in unexpected sinking of the vessel.
* Exterior ighting systems have significantly different requirements; Boats are required to have navigation and anchor lights.
* Anchoring system.
* Radar is essential for foggy conditions or night time navigation. Many of the maintenance issues are similar, but some that are unique to boats are:
* Zinc anodes on external metal parts and internal metal parts that come in contact with water.
* Bottom paint to retard growth which would significantly affect speed/performance. Some caveats:
* As with RVs, boats come in a large variety of sizes and with a different set of amenities. Clearly, a small trailerable fishing boat doesn’t have most of the systems and amenities I’ve mentioned above, but neither does a tent trailer.
* The U.S. Coast Guard has regulations and standards that govern many things aboard a boat.
* Because of the marine environment, many components need to be protected against moisture or water.
* Much of the wiring aboard will be flexible and often will have individual strands tin plated for corrosion resistance.
* Because of the high explosion risk aboard gasoline-powered boats, many components need to be ignition protected &/or located outside the engine room.