Westerbeke 21A Installationshandbuch PDF herunterladen (Seite 34)

RAW WATER INTAKE

Raw water should be supplied to the raw water pump

through a standard-type through-hull fitting, located on the

hull so as to be below the waterline during all angles of boat

operation.

The raw water should be directed from the through-hull

fitting through a seacock, to a visual-type raw water strainer,

and then delivered to the pump. The strainer should be of the

type that may be withdrawn for cleaning while the vessel is

underway, and should be mounted below the waterline to

ensure self-priming. Seacocks and strainers should be at least

one size greater than the inlet thread of the raw water pump.

Hoses routed from the through-hull fitting to the strainer and

to the raw water pump should be wire-reinforced to prevent

the hose from collapsing during the engine/generator’s

operation (suction from the pump may collapse a

non-reinforced hose).

Make sure this system is in proper order. Check that the hull

inlet, seacock and strainer are unobstructed. Inspect the raw

water lines to make sure there are no collapsed sections

which would restrict water flow. Make sure there are no air

leaks at any of the connections; use double clamps on hose

connections below the waterline.

Be sure that the raw water intake is clear of any cavitation

created by the propellers.

The raw water intake to the engine or generator should be

separate and not combined with any other inlet for the main

engine(s) or air conditioners. The use of “sea chest” intakes

is permissible but they must be engineered to provide an

adequate supply of water for all equipment connected to

them.

A through-hull fitting that is completely flush with the

surface of the boat’s hull and without an external strainer

may be necessary for the generator raw water intake on very

high-speed boats. The protrusion of a standard type through-

hull fitting and a strainer can cause a venturi effect on the

intake of a high speed boat, creating a suction which works

against the raw water pump causing an inadequate supply of

cooling water to the engine.

If a generator set is located above the waterline of the boat, it

is good practice to provide a loop or loops above the inlet of

the raw water pump in the raw water supply hose from the

raw water strainer. The loop(s) provide a head of water on

the raw water pump which, on start-up, lubricates the pump

impeller until the pump starts drawing water from the intake.

RAW WATER OUTLET

Wire-reinforced flexible hose should be used between the

raw water outlet on the heat exchanger and the exhaust

system. This reduces vibration and permits the engine to be

moved slightly when it’s being realigned.

FITTINGS

All pipe and fittings should be of bronze. Use sealing

compound or tape at all connections to prevent air leaks. The

neoprene impeller in the raw water pump should never be

run dry. All hose joints should be double clamped with

304/306 stainless-steel hose clamps. T-bolt clamps are even

better but must be 304/306 stainless.

COOLING SYSTEM

▲ CAUTION:

Do not use a high speed scoop-type

through-hull fitting for the raw water supply for

generators and auxiliary sailboat engines as it will tend

to encourage siphoning. Water pressure against this type

of fitting while the vessel is underway with the

generator off or when sailing can push water past the

raw water pump impeller and into the exhaust system,

filling it and the engine as well.

▲ CAUTION:

Water intrusion into the engine through

the exhaust system is not covered by warranty.

▲ CAUTION:

On some extremely high-speed boats,

the use of a sea scoop type strainer may be necessary to

provide an adequate supply of cooling to the generator

when the boat is underway. If this is necessary, the

exhaust piping from the generator must have a

continuous downward pitch to the outlet at the transom

so that no water can be trapped and back-up into the

engine. A solenoid operated shut-off valve can also be

installed in the raw water supply to the raw water pump

and wired to close when the generator is not in

operation.

▲ CAUTION:

The use of common street elbows is

not recommended in plumbing the raw water circuit.

These generally have a very restrictive inside diameter.

The use of machine-type fittings is preferred.

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