Gearboxes converting?

[ShipsWoofy]

I have to get new props, especially on my port engine. HAve been considering prop rotation.

Both engines are right hand and it would be better for steerage if they were opposite, so if I was to get a left hand prop,

1. Would it be a problem running an engine permanently in reverse?

2. Is it feasible to just swap over the final drive cogs in the gearbox to have a left hand box, can I do this without workshop presses etc.

3. Should I live with it, it is not a massive problem, but I feel slow speed manoeuvring would be improved, even though the props are 12ft apart.

Any advice, thank you in advance....

<hr width=100% size=1><A target="_blank" HREF=http://www.topcatsail.co.uk>Woof</A>

 

[Robin]

Some Volvo gearboxes are indeed reversible as standard. We had a new MD22L fitted into our last boat and ran the gearbox reversed merely because it left the prop kick as it was on the old engine, so I didn't have to think about it. All that was entailed was to change the cables on the gear control end. I don't know if you can do that on Yanmars/Hurth though.

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[boatmike]

Indeed it depends on the gearbox. There are cone types and disc types. Some can, some can't. Suggest you ask the official Yanmar agent in your area to be completely sure but there is a good chance that you can run in gearbox in reverse with no harm. Quote to him the gearbox make, model and year and he should be able to answer your question definitively.

<hr width=100% size=1>

 

[Robin]

You would also need to check if the reduction ratio in reverse is the same as in forward, since otherwise the propeller diameter and/or pitch will need to be different as well as the direction of rotation.

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[oldharry]

Contra rotating props will definitely improve handling. Running permanently in reverse would depend on how reversing is acheived in the boxes. Some boxes are designed to run either way, but most involve extra gearing to acheive reverse which will create more drag (= higher fuel consumption and less power available at the prop). Some types have a friction clutch to engage reverse, which is not designed for sustained use at high speed, and would fail quite quickly. Also some boxes have different reduction ratios in reverse.

You need to check out with the box manufacturers.

'...Swapping over final drive cogs...' ,might just work if you are lucky, but it is unlikely to be that easy. Similarly, the need for a press. It would depend entirely how the boxes are assembled in the first place.

The handling benefits to be acheived certainly make it worth investigating further.

Good luck

<hr width=100% size=1>

 

[boatmike]

Agreed,
I can think of several other considerations too thats why it is important to consult the specific specification of the gearbox with the manufacturers. If he is lucky its simple, if not they will be able to advise what is and is not possible on his specific gearbox.

<hr width=100% size=1>

 

[salamicollie]

I seem to remember that you have 1GM's - these have a different ratio for reverse than forward, therefore swapping the change round to put one in reverse might leave you going round in circles!

I guess its time to talk to Dickies (Grrrr...) I cant recall any mention of alternative rotation options in the workshop manual, but it could be possible to change the gearboxes to another type perhaps.

<hr width=100% size=1>

 

[steve6367]

On that note..........why do they have a different ratio? Mine is like that and just seems to be a pain really............is there a use?

<hr width=100% size=1>

 

[oldharry]

Re: Different ratios

Usually to do with the design of the box - making manufacture simpler or the box smaller by using a smaller reverse drive gear, and thus changing the ratio. Also possibly because props are much less efficient in reverse, particularly at high revs so the ratio is set to take account of this and give the prop a better chance to bite the water in a 'full emergency astern' situation.

<hr width=100% size=1>