Propeller Basics

The follwing information is provided to help you understand the basics involved in selecting an appropriate propeller for your boating use. It is not meant to provide expert advice. The best fit for your propeller application is determined by several factors, including your boat's current performance and condition. If unsure whether a propeller is right for you, or if you have specific questions about a propeller's application, consult your local boat mechanic.

New and Used boat props

3 or 4 Blades?

A 3-blade propeller usually offers top speed performance while a 4-blade propeller provides maximum thrust and smooth cruising operation.

Diameter:

Diameter is the distance across the propeller from blade tip to blade tip. Calculate the diameter of the propeller by measuring from the center of the shaft hole to the tip of a blade and then multiply by 2. (Example: a Propeller measures 7 1/4 inches from the center of the shaft to the outermost tip of one of its blades. The diameter = 7 1/4 X 2 = 14 1/2 inches)

Pitch:

Pitch is the distance a propeller will move through the water for each revolution. For example, a 21" pitch propeller should move a boat forward 21" each time it rotates, assuming there is no slippage.

Right Hand or Left Hand Rotation:

This refers to whether the propeller rotates clockwise or counter-clockwise. In most cases, right hand propellers are used for single engine applications, and both a right hand and a left hand propeller are used for twin engine application to achieve better steering control.

Cupped Blades:

This is a technique used to enhance the performance of propellers under certain conditions: a cupped propeller will exhibit very high efficiency at high speeds as well as minimize cavitation under heavy loads. To determine if you have cupped blades, feel the blade tips of your prop. They should curve upward on the edges.

Rake:

Rake is a special design feature. Positive rake benefits from normal bow lift to permit the use of a larger diameter propeller, while negative rake can provide extra blade strength for use in very high speed application. A propeller with 20 degree rake has blades that meet the propeller shaft at an upward 20 degree angle

Quality boat propellers

Additional propeller replacement considerations:

• Year, brand, model and horsepower of your exisiting motor.

• What is the current propeller's diameter? (see Diameter heading)

• Aluminum or Stainless Steel?  

• Type of boat do you have? Cruiser, Ski, runabout, bass, pontoon...

Choosing the right propeller for your boat can be one of the most important choices for a boat owner.  There are manufacturer websites available designed to help you determine the best propeller for your boating application based on specific information, but it is always a good idea for you to check with your local dealer.