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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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Old 04-21-2008
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gearbox ratio

I've ordered a new Beta 28hp engine for our 31ft Pacific Seacraft Mariah. The one thing I'm not sure about is the gearbox ratio. They offer 2:1 and 2.5:1.

Our boat is heavy for a 31 footer, at 16,000 pounds. I don't totally understand this area of propulsion. Can anyone offer an opinion? Note that we will be buying a new prop once the decision is made.

Thanks for any advice.
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Old 04-21-2008
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What was the existing gearbox ratio and prop? Did it move the boat well enough?

It is notoriously difficult to get this right. The designer normally puts quite some time into doing so.

It is similar to trying to match the engine, gearbox and wheel size (prop) on a motorcycle. If the wheels are too small, they spin all the time (and your prop is like a food whisk). If the wheels are too big, they labour the motor, (and your prop is like the paddle on a paddle steamer and too much drag on the motor... it never gets up to speed).
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