Left Handed Prop

[jongleur]

Could my Universal M25XP be spinning
in reverse when I think it's in forward?

Is there any chance that I need a left
handed propeller? If I put a left handed
prop on what problems might I be
incurring?

[ddsailor25]

Your owners manual will tell you what rotation you need for your prop. If you put a left rotation prop on bad things would most likely happen if it's suppose to be a right rotation.

[ddsailor25]

If you google your engine like I just did the first hit says R rotation.

[captain58sailin]

First check to make sure your linkage is not attached wrong, so that when you think you are putting the reduction gear ahead, it is really engaged going astern. Try putting the reduction gear ahead by hand with no linkage attached and see what happens. If you are at the dock, make sure your mooring lines and cleats are sufficient to withstand the strain. Need some more information before useful advice can be given, How did the unit come to be in your vessel? Is it original equipment or a repower? Is the RH propeller original equipment or a new addition? I went to the Universal site, do you have a hurth reduction gear on yours?

[jongleur]

58:

Yes, good questions. I have read some literature.
The mechanic that checked out the motor said the
shaft is spinning left handed while in what he said
should be "forward" for this engine and trans, but it
has a right handed prop on. I asked a diesel mechanic
and they said this diesel rotates "left handed".
Yes, the linkage is connected "backward". Yes, it
has a Hurth transmission.

I recently bought the boat from the original
owner who is not able to answer any questions.
Yes, it is a re-power, apparently from an Atomic
4 to the M25XP somewhere in the 1980s or 1990s.

Backs up well but going ahead is for squat.

That's why it's so confusing.

[captain58sailin]

I am not conversant with hurth reduction gears, but on a Borg Warner you are able to switch the selector valve on the transmission to the other side and change the rotation. These transmissions are just a pump and if you redirect the flow it will change the rotation. I don't know about Hurth's though, they may have a specific way they need to rotate. I would guess the prop is probably from the original engine configuration, which depending on the hp and gear ratio, of each unit, you may need to change your prop anyway. Maybe not, but it will take some digging to find out. If you have to change your prop due to gear ratio then you might as well get a LH one rather than changing your reduction gear rotation.

[jongleur]

58:

" Borg Warner you are able to switch the selector valve on the transmission to the other side and change the rotation."

That would be awesome if I could just change
the way the transmission turns.

Anybody know if Hurth has a selector valve?

[captain58sailin]

http://www.nathape.com/res/Logoundan...anualowner.pdf

[Jim Cate]

Originally Posted by jongleur

58:

" Borg Warner you are able to switch the selector valve on the transmission to the other side and change the rotation."

That would be awesome if I could just change
the way the transmission turns.

Anybody know if Hurth has a selector valve?

No, the Hurth is a mechanical tranny, not hydraulic, so you are outta luck there, mate.

Jim

[Lodesman]

Originally Posted by jongleur

Backs up well but going ahead is for squat.

Is the prop on backwards?

[jimbunyard]

If you have a Hurth transmission, I believe that you can use either position for forward or reverse. The difference is the final gear ratio, one position is higher geared than the other, because of the additional internal gearing necessary to change the direction of the rotation. There is also a slight decrease in rated power input allowances for a 'backwards' configuration. This may or may not be an issue, depending on what model gear you have, in respect to the hp of your engine.

Based on your statement "not going ahead for squat", I'm curious if the forward clutch plates might be worn. If this is the original (repowered) gear from the 1990s, it might well be expected that the reverse plates are still good since far more time is spent in forward than reverse.

Regards

[cappy208]

It would appear that the original shaft and right handed wheel was used. One would think , ah. No problem. Just use 'reverse' as Fwd. And 'forward' as reverse. Except for the difference in reduction between the fwd and reverse gear.

You will have to get the reduction gear SN and numbers to find the manual. You will probably find a 3:1 (or so) ratio for ahead. And 4:1 or 5:1 reverse.


On the other hand, the clutch bands could just be out of adjustment.

You have a double tough job, since you DONT know what you have, and even the ex owner isn't sure what was done.

Is the 'lack of oomph' equal every time you use it? Or does it vary? If it stays relatively the same I would suspect the transmission is simply being used in reverse already.

[jongleur]

jimbunyard:

Thanks for that. It eases my mind a bit.

cappy208:

Thanks also for your info. Apparently the
previous owner ran in reverse, thinking it
was forward. It is always slow in forward.

Years ago, I was told that a transmission
doesn't lubricate as well when going in
reverse. It may not apply here. I hope
it doesn't.

[jongleur]

58:

Don't know where your link was supposed to
take us. I got a 404 error.

[cappy208]

Do you have the manual? Or can you find one? It should have a diagram of Fwd and Rev. I would bet dollars to donuts that yours is simply being used backwards. The solution would be to get the proper rotation prop. But before you go for a haul out, ensure the facts of the F. N. R. Lever on the transmission. See which way the lever actually lays when it is in F. Compare that to the manual.

An interesting aside, Most 30 to 40' yacht transmissions are not actually reduction gear, but simply F N R controls. Sailboats because of their relatively low speed and very low HP usually do have reduction in the gear. Especially reverse. Or the little engine would stall when put into reverse


Next time you check out powerboats note the phrase 'direct drive' when the transmission is discussed. That's a straight 1 to 1 right out the back of the engine to the shaft. If that were your case, then there would indeed be no difference between F and R. But I suspect your transmission is geared desperately for F and D.