How to Select a Boat Prop

Author: reikopena | Posted: 20.04.2012

A boat’s performance depends on the selection of the right propeller. Choosing the correct size and style of the propeller will keep the engine operating within its recommended rpm range and allow it to apply its maximum horsepower to the water.

Getting the right size:

To choose the correct size one has to refer to the diameter and pitch. Diameter is twice the distance from the centre of the hub to the tip of any blade. Generally smaller engines and boats have smaller diameter props and the larger engines and boats have large ones. Pitch refers to the forward movement of the propeller through one complete revolution measured in inches. Lowering the prop pitch will increase the acceleration and pulling power. A higher pitch prop will make the boat cruise faster as long as the engine has enough power to keep the rpms in the optimum range..

Number of Blades:

If the number of blades is changed, the pitch and diameter will require minimal adjustment to keep the rpm within the proper range. However 3 or 4 blades can be used interchangeably on the outboards and stern drives without much effect on performance.

Material:

Boat props can be made of composite aluminum or stainless steel. Composite props are durable, inexpensive and good in performance. Aluminum is the most suitable as they have various applications. Stainless steel propellers are the most durable and offer the best performance.

Cupped Propeller:

Propellers which have curved trailing edges are able to maintain performance at higher trim levels and at tight corners. They allow most boats to achieve higher top end speed and also promote efficient fuel consumption.

Wide Open Throttle:

The prop should be selected in a manner to allow the engine to reach its optimum WOT which is about 5000to5500 for outboards and 4400 to 4800 for stern drives depending on the engine type.

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