Marine engine environment
14
Typical sample of a planning hull and how displacement and engine output tolerances effects
performance
Nominal engine output
Engine output ±3%
Propeller precision
tolerances ±3%
Nominal displacement 13 tons
Displacement ± 3%
Thrust/
power
Speed
Knots
20 22 24 26 28 30 32 34 36 38 40
20
22
24
26
28
30
40
38
36
34
32
Max. tolerance
range
Displacement / hull
resistance
C
Engine output / Thrust
A
B
C)
A)
B)
Production tolerances
In order to ensure optimal performance of the vessel
and long engine life, correct propeller size is essential.
Selecting the correct propeller will enable the engine
to develop its full power and provide the performance
that is expected.
There are a number of factors with their tolerances
that can greatly affect the performance of the vessel.
These must be recognised for correct engine/propeller
selection. These factors are:
A) Engine power can vary within international power
standard tolerances.
B) The calculated hull resistance/displacement may
vary within certain limits.
C) The power absorbed by the propeller with regard to
propeller manufacture precision tolerances general-
ly affects engine rpm.
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