The use of Trim Tabs
The use of Trim Tabs – part 2
The relationship of the Torque, Thrust and Gear Ratio
The relationship of the Torque, Thrust and Gear Ratio
The use of Trim Tabs
The use of Trim Tabs – part 2
The relationship of the Torque, Thrust and Gear Ratio
The relationship of the Torque, Thrust and Gear Ratio

The lower unit Gear Ratio and its importance

By Thomas P.

The propeller rotates at the same speed with the propeller shaft, while the propeller shaft usually rotates much slower than the engine crankshaft turns, at the same throttle setting. This is due to the reduction gear which exists on all the outboard engines among their crankshaft and propeller shaft. 

Gear ratio (or reduction ratio) is expressed by the number of crankshaft revolutions for one revolution of the propeller.

In other words, if an engine has a 2:1 gear ratio means that for one revolution of the propeller the engine crankshaft turns twice.
We can easily find the propeller shaft rpm by dividing the engine rpm with the gear ratio.

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The lower unit Gear Ratio and its importance
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