The dimensions of a propeller are usually stated with two measurements, for example, 14 x 17 (this does not apply to DP propellers, the dimensions of which are stated by means of a special sizing code). The first of these two measurements refers to the diameter of the propeller – 14" (A). The second measurement refers to the pitch of the propeller – 17" (B).
A rotating propeller describes a circle (A) – the diameter of this circle is also the diameter of the propeller.
The pitch of the propeller refers to the distance (forwards or backwards) the propeller moves in describing one complete rotation –this can simply be likened to a screw being screwed into a piece of wood. As water is not a solid substance the propeller will move some 70 to 90% of this distance, D. The remaining 10 to 30% difference is known as “slipî, C.
When replacing a propeller it is absolutely essential to choose the correct type of propeller. Should the propeller rotate clockwise or anti-clockwise?
It may sometimes be difficult to find the size number on a propeller. In such cases, measure from the centre of the propeller hub to the tip of one of the blades and then multiply this figure by two.
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