Domestic water heating via heat exchanger to coil to wet exhaust

[Blackbadger]

Hello,

We are liveaboards and in the process of building our floating home and now installing the hot water supply so we can use an on-board shower facilities instead of marinas. I have fitted a domestic stainless steel indirect cylinder which will plumb into shore power. This is a brand new installation as the boat is an unfinished project.

Whilst completing the plumbing and designing the supply I am wondering if anyone has successfully heated their hot water supply using plumbing into the bowman heat exchanger, redirecting the waste water after the exhaiust manifold through the cylinder coil then return to the wet exhaust. What i am unable to find is the water temperature post exchanger. There are examples of raw water cooled engines adding extra pumps which I would avoid. This would be pressure fed using the jabsco raw water pump, the only alterations needed would be to extend some hose, poetntailly lagging the supply from the engine to coil retaining the heat.

The tank would be connected via rubber hoses and is mounted on a wooden platform, the 220v supply via galvanic isolator should help prevent galvanic corrosion (obviously leadinga a separate discussuon).

Logically this seems to be the simplest method without diverting the closed water supply, complicating the plumbing and at worst, easily to refit the existing loop (which will be retailed) in an emergency should that side fail. Having read about localised cooling and having a ford lehman where overheating could be a problem this method will negate the need to alter the basic cooling system setup which seems fine. Another logical advantage is the engine not heating sufficiently ot taking longer may be a problem like to smoke until reaching operating temp.

Or simply bite the bullet for the cost of a few meters of hose worth trying?

Any advice gratefully received ��,

Thanks Carl.

 

[kashurst]

Hi
the usual way to heat up a hot water tank is to connect the heating coil in the tank to the engines fresh water (i.e. antifreeze side) of the cooling system. This water supply is at @ 90 deg C when the engine is up to working temperature and will heat your hot water quickly. Also you should not have problems with galvanic corrosion. Its usually worth fitting a temperature control valve (one of those things that mixes the hot with some cold to make sure the water at the taps/showers is @ 45 degs max) on the hot water exit as the water can be too hot.

The raw water side of the system that exits into the exhaust elbow should not be more than @ 15 -20 degrees above the sea water temperature if everything is working properly - so not hot enough to heat up a hot water tank. The amount of water going through the raw water system varies with engine speed etc and you don't want to put anything in line to restrict the raw water flow into the exhaust etc otherwise you will have lots of other problems too.

If you find that you want to heat up hot water but not move the boat, and you do not have shore power, it's better to use a seperate generator than run your engine at idle for an hour or so. If you use your main engine very rarely to heat water, your engine will be OK. Do it a lot and you will get other expensive engine issues. You also need to be very very careful about exhaust gases getting back into the boat, its very easy to kill yourself with CO poisoning - so get a CO alarm as well.

 

[Momac]

Hello,

We are liveaboards and in the process of building our floating home and now installing the hot water supply so we can use an on-board shower facilities instead of marinas. .

If you are in a marina simply use the immersion heater which will presumably be supplied with the calorifier . The immersion should be low wattage to avoid overloading the shore power supply.
As stated the heating via the engine for use when on the move should the antifreeze circuit .
Do not consider running the main engine at idle to heat water as it probably will not work because the engine will probably never get up to normal working temperature . Also prolonged running at idle will do the engine no good.

 

[dragoon]

As a previous live aboard, I would keep things as simple as possible. An electric supply with a timing circuit for the immersion heater will be best. If you move a lot, you can use the coolant side of the system to heat a calorifier. Raw water is not suitable - it will likely corrode, block the coil and dezincify any brass internals of the calorfier as well as potentially present a problem for the cooling system of the engine. You'll also ruin an engine in double quick time, as you'll need to leave it at high idle for long periods of time, glazing the bores and generating condensation in the head as it won't get up to correct temperature. It will likely also annoy any neighbours.