Performance Propellers

Extendo Propellers

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Is Prop too small due to repowering?
 
Was your original prop to small?
 
The extendo propeller, a solution to prop space problems.
 
extendo prices start at $360
If your prop is too small, no amount of experimenting with number of blades or pitch will give you quiet cruising in calm conditions, crisp maneuvering astern, low drag under sail and the ability to punch through a head sea. Only larger diameter props give you all these benefits.

Our Extendo props are a simple, bolt on way to get rid of undersized props. We designed a prop with an integral 6 inch long extension on the front. Because of the downward slope of the shaft and the upward slope of the hull, the 6 inch hub extension lets you swing a 2 to 3 inch larger prop on boats with fin keel/skeg rudders.

The Extendo concept is particularly useful for vessels replacing Atomic 4 direct drive motors with modern diesels that have a gear reduction. Most boats that were designed for use with the Atomic 4 direct drive only have room for a 12-13 inch prop. Diesel replacements usually work better with 15-16 inch props. The Extendo hub makes it possible to use a larger propeller with the new engine.

old bronze prop__________3" larger extendo
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The Extendo design clearance

Sometimes the best standard propeller for a motor is larger than will fit on the boat. If the prop is in open water, The special extended hub propeller mounts on the existing shaft but positions the propeller 6 inches aft. This change in position of the propeller, due to the angle of the propeller shaft to the hull, can permit a 2 to 3 inch larger propeller.

 

 

angle hull to shaft                       10        12        14        16        18       20                   

dia chg allowed                         2.12     2.55     2.99     3.44     3.90    4.37                

additional extendo clearence   1.06     1.28     1.50     1.72     1.95    2.18                

 

For example a 12 inch propeller on a boat that has a 16 degree angle propeller shaft to hull can be replaced by a 15 inch extended propeller.

From the chart the radius changes by 1.72, by adding the radius change to the shaft to hull dimension previously found the new hull to shaft dimension is:  8+ 1.72=9.72 about 9 3/4”  The change in propeller location allows 14% clearance on a 15 inch propeller.

 

The extended propeller can make a difference when re-powering from an older gas motor as the Atomic 4 with direct (1:1) drive to a modern diesel with a gear reduction. There are several popular boat models where a more powerful geared motor needing a 14 or 15 inch propeller was placed in a boat designed around a 12 inch propeller than can benefit by using the extended propeller.

For boats with propellers in tight apertures, the Extendo hub is not an option so you have to settle for just the gains of better aerofoil shape and flex pitch.

information on our flex (variable) pitch technology used in the extendo propeller.

guide to propeller design and selection

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Performance Propellers


44 James Street                                     Phone 607-749-3165

Homer, NY 13077                             Fax 607-749-4604

Email performance.props@verizon.net