Transmission Lesson

" Question for the experts out

" Question for the experts out there. I have a BW transmission. 1:1 ratio, and I see the same transmission with 2 or 3:1 ratios and I am wondering about the effective differences. I imagine that means 2 or 3 revolutions to the prop for every 1 rotation of the engine. Basic common sense tells me my transmission will provide better acceleration, with lower top end speed. In a 32' Fairliner(or similar vessel) with twin 318s, how well does it perform with the various transmissions? "

"Actually, it's just the o

"Actually, it's just the opposite for the reduction ratio. 2:1 means two engine revolutions to 1 revolution of the prop. It's like low gear in your car, multiplying torque and allowing the engine to rev higher for a given prop RPM.

Generally, reduction gears are used in larger, heavier boats where a 1:1 ratio combined with a common prop size would overwhelm an engine. Prop sizes (diameter and pitch) can be used to accomplish the same thing, but within a limited range of efficiency. So a reduction gear combined with an effective prop size are used to match engine speed with a targeted boat speed.

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