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

EXHAUST SYSTEMS
There are two main types of exhaust system:
1) Standard yacht - wet exhaust system with a water
injection bend and waterlock silencer
2) Dry exhaust system (see page 17)
STANDARD YACHT - WET EXHAUST INSTALLATION
Owners need to be aware of three major problems that
can easily occur when installing an engine in a sailing
yacht or motor boat and allowing the engine to 'hydraulic
lock'.
• Seawater syphoning past worn impellors in the
seawater pump, flooding the exhaust system, and
back filling into the combustion chamber when the
engine is stopped.
• Seawater washing into the combustion chamber from
the exhaust system due to either a very shallow
exhaust run from the injection bend to the waterlock
silencer, or because the waterlock silencer is too small
to accept the total amount of cooling water in the
exhaust hoses, or both. This can happen when the
yacht is sailing into a big sea and a surge is set up in
exhaust system as the yacht pitches - with the engine
switched off.
11 Standard Exhaust System
25 cm
Normal Sea
Water Level
We recommend care when designing your exhaust
system. The most important aspect is to ensure that water
cannot enter the engine's combustion chamber from the
exhaust system (this applies to both wet and dry exhaust
systems).
• Waves forcing water up the exhaust due a poorly
designed system with no 'gooseneck'. Small work
boats moored on exposed beaches are very vulnerable
to this as waves hit the stern before the boat can
swing into the wind on a rising tide.
It is therefore very important to ensure that the engine will
not 'hydraulic lock'. This can be a problem with engine
installations. Water enters the combustion chamber and
'hydraulics' against the rising piston, this results in bent
con rods, emulsified engine oil and a wrecked fuel pump!
It's best avoided!
If your engine is installed below the water line, the
potential for water entering the engine is considerably
increased. The important dimension that must be
measured is from the normal 'static' sea level to the point
at where the cooling water is injected into the exhaust -
this should be a minimum of 25 cms.
Waterlock Silencer
Rope Cutter
11
40 cm
Propeller Clearance