How to find the gear box ratio

Started by offken, September 08, 2009, 19:34:16 CET

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offken

I have two hurth Hsw 250 A gear boxes in my boat and I would like to know there ratio, the problem is that there is no name plates on them . Can some one tell me how can I find the ratio please .
                                 Thanks
Coronett powered by twin Isuzu 2.8

Granitu

normally they are 2:1

the instructors manual should have
Good season so far.....

nando_s

Quote from: offken on September 08, 2009, 19:34:16 CET
I have two hurth Hsw 250 A gear boxes in my boat and I would like to know there ratio, the problem is that there is no name plates on them . Can some one tell me how can I find the ratio please .
                                 Thanks

Hi offken, there are two available options for that gearbox. In the first case the forward and reverse ratio is the same namely 2.737 : 1. The second configuration you have different forward and reverse ratios, 2.737 : 1  and 2.227 : 1. Which ratio is used as forward in this case depends if you are using a right hand or left hand prop.

Although most gearboxes for light duty and pleasure are 2:1 or close enough you cannot assume anything. Each boat/prop/engine setup is unique.

joe

#3
turn the main shaft one full rotation and see when looking at the prop how much it will turn.

nando_s

Here is the spec sheet for your gearbox. Note that Hurth changed all the gearbox model names and this is what your HSW 250 A is equivalent to today.