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gearbox ratio

im having a 58ft semi trad built with a beta 43 engine and 150 gearbox.i intend to use canals and rivers, would you recommend a 3:1 or 2:1 gearbox ratio.

Asked by: d baird  | 7.25pm, Thursday 14 April

WW says:

I does depend on what size propellor you want to fit (or can manage to accomodate)- most people would go for a 2:1 gearbox, and a suitable prop, but it depends on what you can fit. A 3:1 prop will turn more slowly, but need to be correspondly bigger and, depending on your draft, height of sternpost, etc, you might not be able to fit a suitable size- though you can trade off increase in diameter with pitch.
For best advice, consult your builder about the prop size you can fit, then consult a propellor specialist. Sizing a prop/gearbox combination is not just a matter of choice, there are calculations which need to be done.
A mismatched prop and gearbox would cause the engine to labour, or not deliver enough power at a suitable speed.
Hope that helps!

Mark Langley  | 9.40PM, Thursday 14 April

You might also want to consult a prop specialist, such as Crowther, or one of the new designs, such as Axiom, for their advice.

Mark Langley  | 10.41AM, Friday 15 April

Readers say:

thanks for the reply, will ring and consult beta themselves as there is a lot more involved than i thought

d baird  | 7.51AM, Friday 15 April

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