Venture 23 (C Dory) Hot Water Heater?

Playing around with some water heater formulas and suppliers on the 'net. Back of the napkin:

Let's say I just wanted 2 gallons of warm(-ish) water to shower with and I was willing to run my engine either during a trip (duh!), or idling at anchor.

The idling case above is the worst case:

The Honda BF150 says it can generate 20A while at idle (maybe).

At least one online water heater formula says that #WATTS / 2.42 * degF rise in an hour = number of gallons of water.

So, if I generate (with no battery depletion) 20A*12V=240Watts and I am willing to tolerate 30degree warmer water than the temperature of what is in the cold water tank, then:

240 / 2.42 * 30 = 3.3. Meaning a 240 watt 12V element will heat 3 gallons of water in one hour of the engine idling. There are lots of 100, 200, 300, and 600W, 12V elements on the net.

A 2 gallon tank would then only take 2/3 of an hour of idling, I assume. Any errors in the calculations could be assumed to be taken up by the house battery bank.

Seems to me a dual element (120V for shore power and 12V for engine/battery) and a smallish 2-gallon water tank with TONS of insulation might be an interesting thing to consider.
 
Ray":lz8rhxys said:
Playing around with some water heater formulas and suppliers on the 'net. Back of the napkin:

Let's say I just wanted 2 gallons of warm(-ish) water to shower with and I was willing to run my engine either during a trip (duh!), or idling at anchor.

A 2 gallon tank would then only take 2/3 of an hour of idling, I assume. Any errors in the calculations could be assumed to be taken up by the house battery bank.

Seems to me a dual element (120V for shore power and 12V for engine/battery) and a smallish 2-gallon water tank with TONS of insulation might be an interesting thing to consider.
Click to expand...

Great calculations and all true, but a 2/3 of an hour idling a 150 HP outboard is a very inefficient way to heat water 30 degrees. (fuel use, wear and tear on the motor, plus noise, exhaust etc) Solar water heating (assuming that you hail from an area where the sun shines, running a 1000 watt generator for 10 minutes, or 2000 watt generator to heat the 6 gallon tank--again, are far more efficient fuel wise--assuming that you have need for the generator.
 
Thanks.

I was holding off on typing the obviousness of that just so I could get through the exercise..

:lol: :wink: :lol: :wink: :lol: :wink:
 
I can tell you from recent memory on our Pender Harbour / Princess Louisa Inlet cruise that per the Victron the BF150 at idle is NOT putting out 20 amps. Don't remember exactly what it was, but remember being surprised at how low it really was. I am not going to jeopardize my batteries with some large current hog on an inverter. I would power any hot water heater with the generator for sure. We have a Honda 2000i, since we decided we did not need a microwave, I am wondering if we would not have been better of with a 1000i. Water under the bridge now of course.

But I will for sure be looking at the Home Depot 2 gallon point of use water heater to mount under the galley, assuming it will fit behind the ARB freezer. Or some other small size point of use hot water heater with more amenable dimensions. Unless the water heater is close to where the hot water will be used, there is just too much waste while the hot water gets to the faucet. If not, we are happy with low tech solutions like heating water in the tea kettle for washing dishes, or showering like Kerri On's garden sprayer! Plus at Powell, we can use lake water for this (if we need hotter water than just jumping in the lake!).
 
Pat,

Since you took out your factory 6 gallon unit, it would seem almost a slam-dunk to install a small tank unit near the sink. OTOH, as I've thought about the issues in this thread, the question I'd have is: How long after the water is hot (say 2 gallons) does the water remain useably hot? I'm going to assume that the insulation in these small units is not as good as the 6 gallon unit. So once the generator is turned off, how long does one still have the benefit of at least mildly hot water?
 
JMO but after a day of boating, hiking, crabbing whatever....a nice hot shower is FANTASTIC. Twenty minutes of generator noise and I go to bed clean.
 
I Installed a Nautic Boiler (Quick makes them). My goal was to keep every appliance 700 watts or less. This water heater is 25 L, round, 600w draw, 316 stainless tank (well insulated). It heats in about 1 hour and holds heat for many hours without power.

We had our boat built with the sink to the rear of the cabin, so the WH is mounted on the rear bulkhead and under the sink (almost instant hot water).

If I were redoing this installation, a better choice might have been the 20 Liter model which would mount horizontally under the helm seat (save some space but slightly smaller capacity).
 
I had a PM which asked about non pressurized tanks in the rapid heat flow thru tanks. The spigot is open to the tank, with no valve between. The tanks is much easier and cheaper to build if it is not pressurized (and I suspect does not need the same certifications of pressure to 80+ PSI). When you open the faucet handle it allows water to flow into the small tank, where it is heated, and then hot water flows out the top of the tank thru the spigot. Thus there is very little pressure in the tank--but normal pressure in the water lines.
 
Thanks to some excellent suggestions from thataway, I've devised a relatively easy to install scheme to eliminate the waste of water that occurs when one must run the galley hot water faucet for a while. wasting that amount of water, until the hot water arrives from the hot water heater located on the other side of the boat.

I sort of high jacked this thread to rise this issue; so once I get around to testing and implementing this scheme, I will post the results to a separate thread in case someone else is interested in solving this issue.
 
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