The relationship of the Torque, Thrust and Gear Ratio
The «Deadrise» of the hull and its importance
The relationship of the Torque, Thrust and Gear Ratio
The «Deadrise» of the hull and its importance
High Gear Ratio vs Low Gear Ratio
It is a fact that every manufacturer of outboard engines installs different gear ratios while we see that as the horsepower decreases the gear ratio gets higher (numerically), which means the revolutions per minute of the propeller decrease.
As we have seen in previous articles, everything is a matter of Torque and combination of propeller’s diameter and pitch.
Let's see the gear ratios that Suzuki and Mercury use on some of their 4-stroke outboard engines:
Suzuki
300hp 2.08:1
250hp 2.29:1
200hp 2.50:1
Verado
300hp 1.75:1
250hp 1.85:1
200hp 2.08:1
We note that at the same horsepower, Suzuki’s gear ratios are higher (numerically) than Mercury’s. That means e.g. on a Suzuki 300hp, at the same engine’s rpm, the propeller shaft rotates more slowly than a Verado 300hp.
At 4000rpm the prop shaft of Suzuki 300hp rotates with
4000 / 2.08 = 1923.07rpm, while of Verado 300hp rotates with 4000 / 1.75 = 2285.71rpm.
At 6300rpm, the prop shaft of Suzuki rotates with
6300 / 2.08 = 3028.84rpm, while on Verado at 6300 / 1.75 = 3600rpm.
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