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.
Why some outboards will overheat while running?
Generally speaking, there are three reasons for this problem. The first reason is the cooling water passage was blocked, so you should check whether the outlet of the outboards has normal water current. We recommend you change your impeller every year at a minimum depending on the amount of use you put on your outboard. One thing to remember is that even if you only use your outboard a couple of times a year you still need to have your impeller checked/replaced every year. Water pump impellers are made of rubber and will deteriorate over time even without being used (commonly referred to as “dry rot”); this can be just as damaging to your water pump as wear and tear. The second reason is that the oil is too short. The last reason is that the end users start the engine out of water and then make the water pump to be damaged.
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