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EXHAUST BACK PRESSURE
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).
EXHAUST HOSE
Wet exhaust hose should be matched to the injection
bend diameter. An engine correctly installed in
accordance with this handbook will meet the emission
requirements of the RCD (Recreational Craft Directive).
PROPELLER CLEARANCE
There must be a propeller clearance between the tip of
the propeller blade and the underside of the hull.
19
Propeller Clearance
Engine
Beta 10 to Beta 25
Beta 30 to Beta 60
Beta 75 to Beta 105
Engine
Beta 10 to Beta 60
Beta 75 & Beta 90
Beta 105
This should be a minimum of 10% of the diameter of the
propeller diameter (some say 15%) to reduce 'tip noise'.
10% of Prop Dia.
x
x
15
Exhaust Back Pressure
70 mm Hg
80 mm Hg
90 mm Hg
Internal Hose Diameter
50 mm
60 mm
75 mm
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