Westerbeke 21A Installationshandbuch PDF herunterladen (Seite 22)

Exhaust Back Pressure (cont.)

Back pressure should not exceed 1.5 psi or 41” WC.

Excessive back pressure can be reduced by increasing E,

increasing the size of the water lift muffler, reducing J, and

reducing G. However A, C, and B should not be compromised

to relieve back pressure.

Back pressure should not exceed the following

specifications:

3 inches of mercury

41 inches of water in the water column

1.5 psi (0.1 kg/cm

)

Sea Trial

A sea trial must be conducted to confirm that no water

intrusion takes place, either via the exhaust outlet or via the

sea water intake seacock. Do not operate the engine during

the trial. Disconnect the exhaust hose at the muffler outlet

and place it in an empty bucket (bucket #1). Disconnect the

sea water hose entering the exhaust elbow and place it into a

second empty bucket (bucket #2).

Select the worst sea conditions available. Operate the boat as

aggressively as possible, putting it through as large a variety

of operating situations as you would ever encounter. Operate

the boat in this way for as long as possible.

Periodically verify that no water enters either bucket. Any

water in bucket #1 is water intrusion via the exhaust outlet.

Any water in bucket #2 is water intrusion via the sea water

intake seacock. Either instance of water intrusion shows that

the installation is not adequate, since you will someday

experience conditions worse than the sea trial.

EXHAUST SYSTEM INSTALLATION

Exhaust Hose

To ensure that engine/generator vibration doesn’t transmit to

the hull, most installations use flexible rubber exhaust hose

for the water cooled section of the exhaust line because of

the ease of installation and flexibility. This exhaust hose must

be marine certified. Provide adequate support for the rubber

hose, to prevent sagging, bending, and formation of water

pockets. Always use corrosion resistant carriers and hangers.

For dry or custom pipe exhaust systems, use a flexible

section, preferably of stainless steel, no less than 12” (30 cm)

overall, threaded at each end and installed as close to the

engine as possible. This flexible section should be installed

with no bends and covered with insulating material. The

exhaust line should be properly supported by brackets to

eliminate any strain on the manifold flange studs.

Make sure that the water discharge into the rubber hose

section is behind a riser elbow or sufficiently below the

exhaust flange so that water cannot possibly flow back into

the engine. Also, in custom systems, make sure that entering

raw water cannot spray directly against the inside of the

exhaust piping. Otherwise excessive erosion will occur.

Dry components of the exhaust system between the exhaust

manifold and the water injected exhaust elbow must be

properly insulated to hold in the heat, prior to the cooling

water being injected.

Scoop-Type Intake

Where generators are installed in very high speed vessels

(50-60 knots), it has been necessary to use a scoop-type raw

water intake to insure an adequate supply of cooling water to

the generator. Generally, this is not recommended, but if it

needs to be done, the generator must be mounted high

enough so that the exhaust piping has a continuous

downward pitch from the muffler to the exhaust outlet in the

hull. The pitch should be adequate so that the muffler will

continuously drain and no water can back-up into the engine

(see illustration).

▲ WARNING:

Do not install rubber hose with sharp

bends as this will reduce efficiency. Do not use rubber

hose on dry type exhaust applications. Doing so may

cause hose failure and leakage of deadly exhaust gas.

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