Steyer Motors 4 Cylinders, Руководство по установке

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Z001007/0_4_September 2007 Page ENGINE INSTALLATION-13
ENGINE INSTALLATION INSTALLATION INSTRUCTION
5. 15. PROPELLER
Too less attention is paid to the propeller and in particular to its efficiency even though it is responsible for
transformation of engine energy into mouvement. Sizing and selection of the propeller mean a positive or nega-
tive decision as to driving qualities as well as fuel consumption.
Voluminous books have been written about right sizing and computation of a propeller. For this reason, the
following information shall serve for better understanding of the complexity and impart basic knowledge.
Of all driving possibilites developped so far, the propeller shows the best efficiency. Sizing of the propeller is
determined by the boat type, the engine power and speed.
5. 15. 1. Dimensions
A propeller is designated by diameter, pitch, number of blades, blade surface, sense of rotation and hole in the
hub.
Diameter of the propeller is determined by:
a) engine power in horsepower or kilowatt-hours
b) propeller speed (number of revolutions of engine divided through reduction of gear)
c) speed of the boat.
It is a wrong assumption that the propeller determines the speed, but it is the combination of engine power with
adapted hull and matching propeller.
The propeller diameter can be approximately computed based on the diagram enclosd, but this only for "water
displacers". Before using the diagram, the max. speed of the ship is to be computed. Only use this diagram for
an approximate computing of the diameter, e.g. for determining the height of the propeller frame. Computing of
the correct diameter and of the pitch is to be done by a specialist. STEYR MOTORENTECHNIK offers this
service to their dealers and customers. If required, please fill in the enclosed form.
5. 15. 2. Propeller pitch
The pitch is the theoretical distance the boat runs at one rotation of the propeller, which is being determined for
100 % by the speed of the boat. Every propeller rotating in water will have a slip. Thus the advance of the boat
will be approx. 60 to 75 % per rotation of the pitch.
Computation of pitch:
A propeller the pitch of which is not exactly adapted to the speed of the boat, will always show a lower efficiency.
To reduce the diameter and then increase the pitch for the same size, which sometimes is required when the
actual diameter cannot be housed, will thus reduce the efficiency.
pitch =
speed (m/min)
rotation of propeller
x slip (%)
pitch =
1200
300
x 0,7 (30% slip)
pitch = 0,357 m