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Marine generators - raw water to keel cooling

Its seems most of the small second hand marine generators advertised are raw water cooled. Can these be converted to keel cooling by diverting the water flow from the exhaust elbow injection point to a calorifier to keel tank and fitting a dry exhaust or is it not as simple as that?

Asked by: Mark  | 1.54pm, Tuesday 4 December


WW says:

It is possible to convert a generator fro raw water to keel cooling/dry exhaust, with a couple of provisos. The water pump for a raw-water system is an impeller pump, which is designed to run with cool water and at an increased pressure. Most keel cooling systems use a simpler, low pressure circulation pump. Impeller raw water units might also not be happy running with an antifreeze mixture (depending on the unit).
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The exhaust elbow may require changing, as it will not now be cooled- and this can effect how the engine runs- it will also be very hot so would need adapting.
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Raw water cooled engines are also designed to run without any form of header tank, so this would need to be incorporated, and would have to be a low-pressure system. re-plumbing the engine cooling water flow might be tricky, but not impossible. The thermostat would most likely have to be changed, as raw-water cooled engines tend to run around 65 C or so, to avoid scaling in the cooling passageways.
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The best advice would be to contact the base engine manufacturer- such as Fairyman, Briggs and Stratton, etc- as they may have kits to convert.
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On the plus side, a raw water cooled engine can be made to be very very quiet, compared to one with a dry exhaust, and possibly endear you more to boaters around you when the generator is running. A water-gas seperator, muffler and waterlock can make a system very quiet indeed.

Mark Langley  | 6.08PM, Tuesday 4 December

The majority of marine generators are designed for the sea going boats rather than inland craft and use raw sea water for cooling. It should be possible to convert a second hand unit to keel cooling.
The cooling impeller pump should be fine, but the extra restriction from a keel cooling system might need an additional or more powerful circulation pump which could be electric.
Ensure that the keel cooling tank is big enough (do not be tempted to plumb it into the main engine cooling circuit) and that there is a vented header tank.
Normally the raw water ends up being injected into the exhaust gases, so plumbing a return pipe might need a modification to the manifold as Mark says.
The extra heat from the dry exhaust might make the use of a cocoon cover impossible without overheating the generator.

Rupert Smedley  | 10.51AM, Wednesday 5 December

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