Beta Marine Beta 50 Operator's Maintenance Manual page 14

PROPELLER CLEARANCE
There must be a propeller clearance between the tip of
the propeller blade and the underside of the hull.
12 Propeller Clearance
EXHAUST SYSTEMS
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.
EXHAUST BACK PRESSURE
Exhaust back pressure should be as low as possible; it
is increased by long exhaust length and sharp bends.
Keep exhaust systems to a minimum length and have
gradual bends avoid tight angled elbows. 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).
This should be a minimum of 10 < 15% of the diameter of
the propeller to reduce 'tip noise'.
x
Engine
Beta 10 to Beta 25
Beta 30 to Beta 60
Beta 75 & Beta 90
Beta 90T, Beta 105T & Beta 115T 85 to 115 mm Hg
12
10% of Prop Dia.
Exhaust Back Pressure
Max. 70 mm Hg
Max. 80 mm Hg
Max. 90 mm Hg