Yanmar (2002) gearbox reverse

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DogWatch

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I need new props for my catamaran and believe it would be desirable to have one left and one right hand prop instead of the current 2 x right hand props as currently fitted.

Is there a reason why I can't swap the cables over in one of my morse throttles and run the gearbox in reverse, is the ratio the same as fwd (currently 2.21:1)?

Also, which is the most desirable, an inward thrust so the prop wash hits some point aft or outward thrust? Inward would seem the most sensible to me, but I am happy to be corrected.

Any recommended prop suppliers?

As an auxiliary question, would someone mind checking my maths on my tapers (which are different like everything else on my soddin boat!) Measured with a digital vernier but unable to remover props (they will probably not come off without damage and the boat needed to return to the mooring), so measured as best I could around the shaft. They are meant to be 1" shafts, so the wide diam. shows my measurements are pretty close. I have not tried to round the numbers, but wrt the tapers, are they close to any standard tapers (is there such a thing) that I will be able to order say wrt port an 11.82 taper for example (hope that makes some sense).

Port

Wide diameter - 0.979
Narrow diam - 0.78
Length - 2.348
My calculation - 11.79 ???

Stbd

Wide diameter - 0.99
Narrow diam - 0.809
Length - 2.072
My calculation - 11.45 ???
 
1" shafts would normally have a 12:1 taper. 1" per foot.
WRT your gearboxes, you don't specify the type, but if they are mechanical, as Yanmars often are, then they most probably can't be run in reverse as you are suggesting. The reverse rotation is produced by introducing an idler gear in the train, which reduces the continuous power rating. For example, the TMC40 gearbox on my Beta has a reverse rating of only 33% of its listed power rating.
At least, ask the manufacturers or agents.
 
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I have found the original receipt for the props currently fitted and it states 1:12 taper, but I know I can't swap them over as the tapers are not identical (prolly find one is metric, par the course on my boat to be honest).

The gearbox was just standard from barras <sic> I don't know without clambering about the engine room what they are, just a normal looking yanmar box, I didn't stipulate anything when I ordered the engines. I suspect I will continue with 2 rt hand props, it was just a thought. I have to change one prop urgently as it had a fight with a mooring chain and came off much worse (one blade is half missing and another has about 1/3 chopped off, it is too pink to try repairing. I need to fit shaft anodes, but don't have much space, will have to either cut one in half or find a supplier of thick ring anodes.

Do you know any good suppliers, my google searching is not going well at all?
 
Acshully >> As one of the props is shorter than the other, see above, I wonder if that is all they did, make them both 1:12 and shorten the stb prop so it would fit. No no no, the taper would be different, wouldn't that mean the prop would go on, but would rattle about? Just thinking out loud you understand?
 
Suggest replace the shafts. 1" imperial is 1:12 taper and new props will be machined for that. as already said, your gearboxes cannot be run continuously in reverse. Not sure about contra rotating props on a sailing catamaran. Don't think that is common/normal. Suggest you talk to Sillette for advice.
 
DogWatch said:
Not rich enough, seems a bit drastic.
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Well, it seems you have a problem if you want to change the props. You don't say what the problem is or why you think contra rotating props are needed. Maybe better to correct the mistakes in the current setup, which might mean only one new shaft and new props. Shafts are cheap compared with props and at least you start off with the proper setup. You asked for recommendation and I suggested Sillette who are prop suppliers and specialise in catamarans.
 
Tranona said:
Well, it seems you have a problem if you want to change the props. You don't say what the problem is or why you think contra rotating props are needed. Maybe better to correct the mistakes in the current setup, which might mean only one new shaft and new props. Shafts are cheap compared with props and at least you start off with the proper setup. You asked for recommendation and I suggested Sillette who are prop suppliers and specialise in catamarans.
Click to expand...

I hadn't realised Sillette was a company, it sounded to me like a PBO user, I'll have a search.

I don't have 'a problem' the boat steers pretty well under engine and will play happily on a single engine, just be nice to have that extra kick when manoeuvring. I don't really see how having slightly odd tapers is a serious problem as long as I know what they are. I mentioned the problem I am trying to fix immediately, there are bits of my port prop on the river bed at my old mooring! :(
 
Not sure contra rotating props will help in that respect. They are normally fitted on powerful high speed craft to help keep the boat straight.

For manoeuvring you use one engine in forwards and the other in reverse - but I am sure you know that already.
 
Yes, but I just thought if it was possible and I was changing the props it would be an opportunity to do it properly and make them contra. Having found one site willing to publish the prices which are similar to Sillette I have decided to change one prop at a time, even though the stbd prop is beginning to pink. I should have bought copper rather than keep savings making zero, seems to have gained more than gold!
 
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