How to find the gear box ratio

[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

[Granitu]

normally they are 2:1

the instructors manual should have

[nando_s]

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]

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.