Propellers have two basic dimensions; diameter & pitch. Diameter is the distance measured across the propeller hub line from the outer edge of the circle that is made by the propeller's blades during rotation. Pitch is the distance that a boat will travel if rotated one revolution without any slippage. When describing a propeller both the diameter and pitch are given. The diameter is referenced first and the pitch is second. Therefore, a 11" x 9" propeller would have a 11-inch diameter and a 9-inch blade pitch.

Theoretically, a propeller with a 11-inch pitch, when rotated one full turn, would advance a boat 11 inches through the water. In reality, no 11-inch pitch blade will advance a boat 11 inches with one full turn. This variance is referred to as slippage. In general, changing to a higher pitch prop will increase your top-end speed but reduce your acceleration (reduce your "hole-shot" power). On the other hand, decreasing the pitch will increase your hole-shot but sacrifice some of your top-end speed. If the hole-shot speed is important to you, for example if you pull water skiers most of the time, then you would want to go with a lower pitch prop and sacrifice some of your top-end speed but increase your hole-shot speed to get the skiers up faster. UNDER NO CIRCUMSTANCES SHOULD YOU EVER USE A PROP WHICH WILL ALLOW YOUR OUTBOARD TO OPERATE ABOVE THE OUTBOARD'S RECOMMENDED MAXIMUM RPM's! Remember that in any application, discrepancies in performance can result due to the different boat hull designs, the final carrying load and your particular needs. NOTE: It is highly recommended that the outboard be checked with a tachometer to ensure that the engine is operating within the correct MAXIMUM RPM RANGE.

2016-07-13

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How can I tell what shaft length my outboard needs to be?

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