Westerbeke 21A Manual de instalación descargar pdf (Pagina 20)

Sea water Intrusion Through The Intake Seacock

Another means of water intrusion is though the sea water

intake seacock. This can occur when any part of the sea

water system or exhaust system are below the worst case

water level (other than the seacock itself which is already

below the water level, of course). What happens is that, upon

engine shutdown, sea water siphons from the intake seacock,

up through the sea water cooling circuit containing the sea

water pump, heat exchanger, and water injected exhaust

elbow, into the water lift muffler. This seawater will siphon

past the impeller of the sea water pump and fill the muffler

and all hoses attached to the muffler until the outside water

level is reached. If the engine exhaust manifold is below the

worst-case water level, seawater will simply pour into the

cylinders, destroying the engine.

This form of water intrusion is avoided by the proper

installation of an anti siphon valve in the sea water circuit

between the sea water pump outlet and the water injected

exhaust elbow inlet. Refer again to the generic drawing of a

below water line engine/generator installation utilizing a

water lift muffler.

K is the difference between the highest underside of the boat

deck near the engine/generator and the anti siphon valve. K

should be minimized. There is every reason to attach the

anti-siphon valve directly to the underside of the deck. There

is no reason to fail to take full advantage of this maximum

available height because it forms the only barrier to water

intrusion by siphoning. The anti siphon valve must be well

above the worst case water level under all conceivable condi-

tions of boat trim, boat operation, sea conditions, and heel

angle. The anti-siphon break and the exhaust hose point

should be located as near to the boats centerline as possible;

especially on sailboats due to large and steady healing. The

siphon must be accessible for maintenance,

Generator-Not in Operation Water Intrusion

Boat operators may be accustomed to seeing a propulsion

engine exhaust outlet dip beneath the water frequently when

underway and think this is acceptable for a generator exhaust

outlet as well. Not so! When the boat is underway, exhaust

pressure keeps water out of the propulsion engine exhaust.

But when the generator is not running, there is no exhaust

pressure to keep water out of its exhaust outlet. The exhaust

outlet of engines which may not be operating when the

vessel is underway – sailboat engines and generators – must

be well above the worst case water level.

Cumulative Process

Water intrusion between operations of the engine is a

cumulative process. If just a little bit of water spills over the

high point, but it happens many times, it will fill the muffler

and endanger the engine. This could easily be the case for a

power boat not using its generator or for a sailboat not using

its engine. If you suspect that water is intruding, run the

engine frequently until the suspected problem is confirmed

and fixed.

NOTE: Running the engine or Genset will normally preclude

water intrusion as the exhaust flow under pressure prevents

water from entering the exhaust outlet.

Cranking the Starter: Draining the Muffler

Prolonged cranking of the starter may cause excessive sea

water to build up between the engine and the high point.

Each time cranking is interrupted additional water may spill

back into the muffler. In time this cumulative spill back can

flood the engine. Unusual cranking and/or cranking

interruptions must be monitored and the muffler drained

before excessive water buildup occurs. This may be made

more convenient by installing a suitable, non-corrosive valve

at the muffler drain fitting.

EXHAUST SYSTEM INSTALLATION

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Westerbeke 21A Manual de instalación Pagina 20

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