On-board systems of power boats vs RVs

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Tom

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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.

Hopefully I don't over-simply or over-complicate this, but I thought a simple comparison might be useful &/or informative. The following lists are by no means comprehensive, just the items that come to mind as I write; I'll add to the lists as I think of more items.

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.
  • Inverter/charger.
  • Converter.
  • DC lights.
  • AC lights.
  • AC receptacles and GFIs.
  • Kitchen/galley extration fans.
  • Generator.
  • 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 either 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 through the hull where the prop shaft(s) enter.
  • Steering is by rudder (except in the case of jet drives). Some power boats also have bow &/or stern thrusters to provide maneuverability in close quarters.
  • Gear shift may be cable, hydraulic or electrical.
  • No suspension components to worry about.
  • No brakes or ABS to wear out or fail.
  • No wheel bearings or chassis lube points.
  • Communications usually VHF for inland or near-shore cruising. Cell phone coverage is often adequate.
  • Air conditioning and heating usually use reversible heat pumps fed by sea water to transport heat into or out of the heating/cooling unit. You won't find an LPG furnace on board, but some boats have a diesel-powered heater similar to the AquaHot systems on some diesel RVs.
  • 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 lighting 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. These have to be changed periodically, more frequently in salt water.
  • Impellers in sea water pumps need to be changed periodically.
  • 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 ingress, water immersion and corrosion.
  • 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 electrical components need to be ignition protected &/or located outside the engine room.
 

caltex

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Not a lot of difference, another common iten is the need to constancly maintain all the systems. Boats and RVs have everything a house has and more, and is seems that they require more work than a house.
 

Tom

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You're right about the constant maintenance of all 3 (house, RV, boat) Robert.
 

Carl L

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Boats, especially those on salt water, need a lot more maintenance -- a lot more! 

One peculiarity is that you do not dare to use unsoldered connectors and the connectors and splices must be protected with adhesive coated shrink wrap or liquid insulator.  Ordinary electrician's tape has a life measured in days on salt water.  Unsoldered, uninsulated connections can corrode all the way up the wire, turning the copper brittle.  Of course there is no frame to ground your system too.  Therefore, each fixture needs a positive and an negative line leading back to the battery.

Any metal under the waterline must either be galvanized or made of bronze.  Under salt water brass will go away in weeks, steel not much longer, stainless steel in months.  (Stainless needs to be exposed to oxygen.)

I learned all this the hard way having to had to rewire a used boat entirely as well has replace a number of not so stainless fitings and screws.
 

Tom

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Good points Carl, from someone who learned the hard way.

Your point about the negative/corrosive effects being magnified when in a salt water environment is well taken. We're spoiled boating here in the fresh/bracken waters of the Delta, but I'm mindful of the salt environment when we go down to San Francisco Bay &/or down the coast.

An example of the difference in required maintenance is the underwater zincs. Here in the Delta I can go 12-18 months without changing them (I usually go 12) but, when we were in your neighboring port of Marina Del Rey, the divers were telling me they change zincs for folks every 3-4 months.

Of course there is no frame to ground your system too.  Therefore, each fixture needs a positive and an negative line leading back to the battery.

Ah yes, electrons don't flow very well through fiberglass.

Any metal under the waterline must either be galvanized or made of bronze.  Under salt water brass will go away in weeks, steel not much longer, stainless steel in months.  (Stainless needs to be exposed to oxygen.)

That's an interesting one. My SS shafts don't have shaft zincs because the boat manufacturer determined they were having too many shaft zincs works loose and slam against the props struts. Every time I have the boat hauled I check those shafts (see photo) and haven't seen any sign of problems. Again, this may be because we're in "fresh water".
 

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dsharp

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When i set up my battery, the only wires I have running to it are from my plotter. On advice from a friend, what I did was soldered the wires from my unit cable to my battery leads, then covered the connections in grease, then shrink tubed them. Terminals and leads are covered in just grease. It has stayed good for almost two years now.

 

Karl

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Tom,
Bottom paint to retard growth which would significantly affect speed/performance.
I'm assuming you're talking about vegetation growth; not the length of the boat ;D ;D ;D

There are many different alloys of S.S., some of which are essentially immune to galvanic deterioration. Looks like that's what you have.
 

Tom

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Karl said:
I'm assuming you're talking about vegetation growth

LOL Karl, the other kind is called "fiberglass fever".
 

Carl L

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dsharp said:
When i set up my battery, the only wires I have running to it are from my plotter. On advice from a friend, what I did was soldered the wires from my unit cable to my battery leads, then covered the connections in grease, then shrink tubed them. Terminals and leads are covered in just grease. It has stayed good for almost two years now.

To save messing around with grease, there is a marine grade of shrink tube that has a thermosetting adhesive inside which gives a full,  and as near as I could see, permanent seal against the wet.
 

Tom

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It's readily available at marine stores Carl, such as West Marine.
 

dsharp

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If I recall, the reason I used it is because we could get it at almost half the price it was at West. I'll mess with the grease and save a little money because I only have 1 connection. I'll probably have the excess for the rest of my life. If I had more...I see your point. ;D

Now I see there is a marine grade COLD shrink tubing. I have used cold brew tea bags, but how does cold shrink tubing work?
 
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