Exhausts And Mounting Exhausts 7 - Beta Marine Beta 10 Operator's Maintenance Manual

Flexible Output Couplings
A flexible coupling should be mounted on the gearbox output flange and is strongly recommended in almost every case.
Flexible couplings do not accommodate bad alignment, they are designed to absorb torsional vibrations from the propeller
(transmitted along the propeller shaft).
Exhausts
We recommend care when designing your exhaust system. The most important aspect is to ensure that the engine will not
'hydraulic lock' - by allowing cooling water into the combustion chamber through the exhaust system.
The basic criteria is when your engine is installed below the water line, the potential for water entering the engine is
considerably increased. The important position that must be measured is from the water line to the point at where the cooling
water is injected into the exhaust - this should measure 30 cms above the water line.
In yachts, engines are mostly installed low down and often below the water line. There are several ways to avoid cooling water
entering the engine:
(a) Syphoning of cooling water can occur when the rubber
impellor of the sea water pump becomes worn. If our
standard injection bend is too low then we can offer a
high-rise injection bend that adds 15 cms to the height.
If this is still not enough then you have to fit an
'antisyphon' valve at least 30 cms above the water line.
These valves need to be checked regularly as they have
been known to block up with time.
(b) We recommend that you always fit a waterlock / silencer
to stop any water in the exhaust system back filling the
engine. The water lock should always be fitted at least
30 cms from the injection bend and about 15 cms below
the injection bend. The waterlock should have sufficient
capacity to hold an exhaust system full of water - draining
into it.
(c) We recommend that you always create a 'gooseneck'
with the exhaust hose (or purchase a propriety one) by
raising the exhaust hose 40 cms above the waterline
before exiting the transom at least 5 cms above the
waterline. This will stop any waves pushing seawater
down the exhaust.
Typical Yacht Exhaust Installation
Warning
(1) One of the most common problems with engine
installations (and often expensive), is 'hydraulic lock'
(water entering the engine combustion chamber). Water
entering the pistons / combustion chamber can cause
bent con rods, emulsified engine oil and a wrecked fuel
pump! It's best avoided!
(d) Keep exhaust systems to a minimum length and have
gradual bends (NOT right angle elbows). Exhaust back
pressure should be as low as possible; it is increased by
long exhaust length and sharp bends. Back pressure
should be measured; with the complete exhaust system
connected and the engine running at full speed. The
correct measuring point is before the injection bend (at
the manifold flange).
Beta 10 to Beta 25 maximum 70 mmHg;
Beta 30 to Beta 60 maximum 80 mmHg,
and Beta 75 to Beta 105 maximum 90 mmHg.
(e) Wet Exhaust hose should be matched to the injection
bend diameter.
Beta 10 to Beta 60 is 50 mm internal diameter;
and Beta 75 & Beta 90 is 60 mm internal diameter.
(f) An engine correctly installed in accordance with this
handbook will meet the emission requirements of the
RCD (Recreational Craft Directive).
(2) The diagram shows a typical exhaust installation. The
rubber hose connecting the heat exchanger to the
injection bend must be replaced by a hose of sufficient
length, connecting to a "T" piece or anti-syphon valve that
is above the maximum seawater level when heeled (at
least 30 cms / 12 inches above the water line) on the
centre line of the boat. The pipe then returns to the
injection bend and the seawater is pumped down the
exhaust pipe.
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