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There are three methods employed for watercooled marine petrol and Diesel engines:
1. direct -
2. heatexchanger -
3. keel cooling
.
Direct cooling of the cylinders and heads by sea-water is un
satisfactory, because the engine - which was probably originally designed for radiator cooling - will run too cold and the seawater will eventually ruin the cylinder block and heads.
Keel cooling is suitable for small boats operating in shallow weedy water, but the need for pipework external to the hull is a severe limitation.
Heatexchanger cooling is the most common method,
the sea-water being isolated in components which can be designed to withstand its corrosive effect. The closed fresh-water circuit can be thermostatically controlled so that the engine operates at its design temperature.
Heatexchangers offered by us are high-quality products incorporating both the best materials and the latest technical features. The tubestack is fully floating, thus minimizing thermal
stresses, and it can easily be removed should cleaning be necessary.
The special structure of the
heatexchanger header tanks prevent aeration of the engine-water circuit which must be designed so, that the system is self-venting on initial filling. It is usual for all the components in the sea-water circuit to be in series,
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the gear-box oil and engine-oil coolers being on the suction! side of the sea-water pump and the heatexchanger and any
sea-water cooled exhaust manifolds being on
the discharge side. In the case of turbo-charged engines the charge air cooler should receive the sea-water first, so that the lowest possible air temperature is obtained. The sea-water outlet from the heatexchanger should be from the end cover equipped with the upper connection, this ensures that the tube stack is always full of water.
The gear-box cooler size will depend on the type of transmission used, but it will usually be a size smaller than the engine-oil cooler.
A water-jacketed exhaust manifold is necessary on marine
engines to reduce the temperature of the engine-room air space, the exhaust pipe and the noise, too.
If the exhaust manifold is in the sea-water circuit it should be installed with the sea-water inlet at the back and the outlet at the front on the top to ensure that it operates completely full of sea-water.
If the manifold is in the fresh-water
circuit a small by-pass hole must be provided in the thermostat to ensure that some water is circulating through the manifold at all times.
An E.-J. Bowman , development is the
C o m b i c o o l e r.
This device
combines a water-jacketed exhaust manifold with the heatexchanger and header tank, which is particularly suitable for small series-produced engines; the manifold is cooled by fresh water and as a result
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a keel-cooled engine can be made by
omitting the heat exchanger tubestack and the sea-water pump. On installation, the fresh-water outlet from the manifold would be connected to the keel pipes and the return taken back to the engine fresh-water pump. Alternative type numbers are listed for these assemblies are listed here.
Combicoolers are heavier than ordinary marine manifolds and must therefore be supported on the underside using the fixing lugs provided!
When automotive engines are being converted for marine
use the existing centrifugal-type pump should be retained for the fresh-water circuit and an additional pump fitted for the sea-water circuit. The seawater pipe bore should be
chosen so that the velocity does not exceed 2 m/sec on the suction side and 3 m/sec on the discharge side of the pump. If the engine is being used to drive auxiliary
equipment in a ship and the seawater supply is taken from the ships main, ensure that the recommended flow rate cannot be exceeded.
If preferred, the oil coolers can be fresh-water cooled; these will
need to be larger owing to the higher water temperature but need not be suitable for seawater. More information can be downloaded from the brochure engine and transmission oil coolers.
When ordering
please state type, number and output power of the engine, as this helps to size the right cooler for your application
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