If your motor is in good condition and your boat is under performing it may be because you have the wrong size propeller!

            We estimate that 30% of older boats have the wrong propeller. Many of the more popular boats were sent from the factory with an undersize propeller.  If your motor gets up to speed before your boat gets close to your hull speed then your propeller may be too small.  If your engine cannot get up to its rated speed your propeller may be too large and bogging down your motor. Fill out a sizing sheet and call 607 749 3165 for a free consultation.

The higher the gear ratio the slower the propeller rotates and propeller diameters are needed. One popular motor supplier offers three transmission ratios for their “20 HP” model. This results in 6 potential propellers:

transmission    propeller          2 blade prop               3 blade prop

Gear Ratio       Shaft RPM      Dia.     Pitch                Dia.     Pitch

2.2                   1455                14        9                      14        9

2.6                   1231                16        10                    15        10

3                      1067                17        12                    17        12

 Obviously gear ratio selection is important to selection of the propeller.

            Many boats were designed for a direct drive gasoline engine operating a  12 inch propeller at 3000 rpm. To save the expense of new molds and designs many of today’s boats still are produced using the same molds and propeller space. If the propeller is not considered when selecting the motor and gear ratio your new motor could need a 17 inch propeller but your boat will only allow a 12 or 13 inch propeller.

            Include the propeller in the motor selection process. Here are a few tips to get started in the sizing of motor gearing and propeller.

Go to Motor and gear selection notes

Go to Determining maximum propeller size