Folding prop question

[puffcard]

My dad bought a new Tayana 42, sailed all over. On a transatlantic the tranny went out, second time in five years. He went into the Canaries and the mechanic verifies that the transmission was installed backwards and it had been running in reverse for years. That was a Hurth. So those will operate in reverse as the main gear, but I believe that it will shorten it's life. After he swap the linkage and bought a new tranny and prop, it ran well for many years.

[Compass790]

Originally Posted by DougR

There are a couple of things to consider here:

- clutch - if it's a cone clutch there probably won't be a problem with the clutch using "reverse" as the primary drive gear as normally the cone surface area is the same on both the forward and reverse side of the cone. If it's a plate clutch it's important to know that the torque handling capacity is the same for both forward and reverse clutch packs, i.e.. Same number of plates on both packs. An example of this is that Borg Warner " Velvet Drive " gearboxes have smaller capacity reverse clutch packs and cannot be run continuously in reverse.

- Reverse mechanism- many transmissions that use horizontal input and output shafts lying parallel to each other obtain their reverse function by directing the power across an idler gear. Frequently this idler gear and it's shaft are not as robust as the main shafts in the transmission, so the manufacturer places a limitation on the amount of power that can be used continuously in the " reverse" gear position. Common examples of this are the mechanical Hurth/ZF gears.

As you point out "the gearbox is massive for the power" so it may be that running in "reverse gear" for forward propulsion will be OK......but it can't hurt to inquire.

One other thing to consider is that many naval architects purposely offset the prop shaft relative to vessel centerline to counter the effects of prop walk and steering torque while underway in forward gear. To change prop rotation in such a case might result in heavily loaded steering while underway.

DougR

whoops I forgot to add you are right it does go thru an idler gear. Not too worried about that tho as all looks more robust than my old motorcycle engine gearbox with 10x the horsepower. Glad you pointed it out tho. Guess there will be a small power loss from spinning an extra gear & shaft but I can live with that

[Wotname]

Originally Posted by Compass790

whoops I forgot to add you are right it does go thru an idler gear. Not too worried about that tho as all looks more robust than my old motorcycle engine gearbox with 10x the horsepower. Glad you pointed it out tho. Guess there will be a small power loss from spinning an extra gear & shaft but I can live with that

I think you will find the forward gear train also includes an idler gear (i.e. forward idler gear) so I expect the end result will be the same.

Mind you, I am not a gearbox expert!

[EWOL Props]

Hi Compass 790, if the engine manual says that sense of rotation can be changed you can do that, otherwise I really suggest to avoid doing it. When someone designs the gears for a gearbox one of the informations needed is if it has to turn preferably in one direction (and which one) or both. That is because the gear teeth can be designed with specific shape to match the type of use.
What happens if you use a transmission in the wrong sense for long ? Well simply: noise, overheating and you can seriously damage the gearbox.

You can do a simple test to prove that...all cars have transmission that are made to turn preferably in forward, if you do some few yards in reverse you will hear a strange whistle noise coming from the transmission....would you run 10 miles like that ? I hope not....

[Compass790]

Originally Posted by EWOL Props

Hi Compass 790, if the engine manual says that sense of rotation can be changed you can do that, otherwise I really suggest to avoid doing it. When someone designs the gears for a gearbox one of the informations needed is if it has to turn preferably in one direction (and which one) or both. That is because the gear teeth can be designed with specific shape to match the type of use.
What happens if you use a transmission in the wrong sense for long ? Well simply: noise, overheating and you can seriously damage the gearbox.

You can do a simple test to prove that...all cars have transmission that are made to turn preferably in forward, if you do some few yards in reverse you will hear a strange whistle noise coming from the transmission....would you run 10 miles like that ? I hope not....

Hi Ewol,I think that i need a more complete mechanical explanation for a reason not to do it actually related to a Kanzaki gearbox than a blanket no with all due respect. The forward & reverse systems in this gearbox are virtually the same, all gear wheels are straight cut. Feel free to laugh if i report back that it's a fail :-). Dont worry I'll be alert to strange noises & overheating issues if I can hear anything above the banging of a 1 pot diesel :-( Actually it never ceases to amaze me what you can notice above the racket.
I lust after your props but I'm not in a position to buy one.

[Compass790]

Originally Posted by Wotname

I think you will find the forward gear train also includes an idler gear (i.e. forward idler gear) so I expect the end result will be the same.

Mind you, I am not a gearbox expert!

Hi Wotname,
Yes it does but if you look in Chapter 9 page 3 of the YSM8 manual you will see fwd idle gear is always in use & reverse idle gear is added to the drivetrain for reverse. At least thats my understanding of their diagrams & ratio tables. I'm obviously not a gearbox expert either.

[Compass790]

Originally Posted by puffcard

My dad bought a new Tayana 42, sailed all over. On a transatlantic the tranny went out, second time in five years. He went into the Canaries and the mechanic verifies that the transmission was installed backwards and it had been running in reverse for years. That was a Hurth. So those will operate in reverse as the main gear, but I believe that it will shorten it's life. After he swap the linkage and bought a new tranny and prop, it ran well for many years.

Thanks, glad to have a real world experience to ponder.

[Wotname]

Originally Posted by Compass790

Hi Wotname,
Yes it does but if you look in Chapter 9 page 3 of the YSM8 manual you will see fwd idle gear is always in use & reverse idle gear is added to the drivetrain for reverse. At least thats my understanding of their diagrams & ratio tables. I'm obviously not a gearbox expert either.

Yes of course, I foolishly was thinking that as the reverse idea gear was engaged, the forward one wasn't - my bad.

Here is a picture to match (almost) what Chapter 9, page 3 denotes. This is the YSE8 gearbox which is much the same at the YSM8 box except it is cast iron, not alloy.

It is looking aft. The O/P shaft (and gear) is at the bottom left(ish). The gears above that to the left are the forward idler while the reverse idler is to the right.
All the gears shown are in constant mesh.

The input shaft/gears engage either the top left train (forward) or the right gear train (reverse).

Thus if you do trial this reverse pitch prop, you will be using the right hand gear along with the left gear when the the boat is moving forward (gearbox selector "reverse"). The shaft is the same size for both sides although the OD of the right side bearing is smaller that the left side bearing. Nevertheless, the size of all the components is way bigger than necessary for 8 (max) hp - IMO.

I mentioned earlier that the clutch did't care but on reflection and a closer look at the clutch - I was wrong. The forward and reverse operations use different fiction material i.e. one side of the single plate clutch is forward and the other side is reverse. Are they actually different thickness or composition - I don't know; my understanding of the manual suggests they are the same and my gut feeling is they are the same but I haven't yet pulled the clutch apart to have a look. Is the friction plate reversible ??? A quick look would tell but right now I don't have the time. Maybe another reader has a YSM8 (or any YS series) clutch plate sitting around and could check?

I do recall reading a couple of years back on another forum about a pommy guy who swore his YSx engine needed a RH prop and everyone telling him otherwise. Turns out that he hadn't realised a PO had done the exact same thing as what you propose. They had also connected the shift cable so that while the position said forward, reverse was selected. He had never realised and apparently it had done no fatal harm.

[Compass790]

Thanks for your post & pic Wotname. I'm 90% sure clutch friction disc is the same both sides.Gud to hear someone else has done it. If you remember the name of the forum you saw the post on about R/H prop i would be keen on contacting original poster. I've cracked & contacted Yanmar but I'm still going to try it whatever they say. Good point about reverse bearing being a bit smaller but i agree as everything seems over-engineered for the h.p. I'm not overly concerned. Suspect they would use the same gearbox on the 15& 20hp twins but I'll check that sometime.
Cheers

[Wotname]

Originally Posted by Compass790

....... If you remember the name of the forum you saw the post on about R/H prop i would be keen on contacting original poster. .......
Cheers

I think it was YBW, similar to (but not) this one Yanmar yse8 rotation
It might have also been a link in one of their threads...
Good luck in hunting it down - it was a few years back IIRC.

[Compass790]

Well Jim I finally took your advice, here is reply from Yanmar FYI

Your enquiry was forwarded to us by Yanmar.

YSM8R gearbox could be run in reverse if used for pleasure application. Not sure of life expectancy as it’s a very old unit.

If you are after parts I could suggest you talk to

Bill Falconer at Falconer Marine 0274849244 he has used parts available and knows this product well.



Regards



Brian Macken

General Manager

Power Equipment Est 1990

Power Equipment Ltd: 156 Beaumont St, Westhaven, Auckland 1010, New Zealand,

This is the NZ agent for Yanmar , not their technical division but at least he did not rule it out.

[Jim Cate]

Originally Posted by Compass790

Well Jim I finally took your advice, here is reply from Yanmar FYI

Your enquiry was forwarded to us by Yanmar.

YSM8R gearbox could be run in reverse if used for pleasure application. Not sure of life expectancy as it’s a very old unit.

If you are after parts I could suggest you talk to

Bill Falconer at Falconer Marine 0274849244 he has used parts available and knows this product well.



Regards



Brian Macken

General Manager

Power Equipment Est 1990

Power Equipment Ltd: 156 Beaumont St, Westhaven, Auckland 1010, New Zealand,

This is the NZ agent for Yanmar , not their technical division but at least he did not rule it out.

Well, good onya! To me, that sounds like it would be quite all right to carry on with your experiment. After all, you are unlikely to run for long periods at WOT settings, as is implied in industrial applications.

Let us know what you decide, and how it works for you.

Jim

[Compass790]

Originally Posted by Jim Cate

Well, good onya! To me, that sounds like it would be quite all right to carry on with your experiment. After all, you are unlikely to run for long periods at WOT settings, as is implied in industrial applications.

Let us know what you decide, and how it works for you.

Jim

Yea Jim. I will be proceeding with the experiment. Tried to fit r/h prop yesterday but will have to machine it's boss & cut down blades & as it was a tidal install I had no time. Will be a few days before we can have another go.
After my cursory dive inspection had guessed that new prop would fit . Wrong! So put single blade back on. Luckily keyway & taper are the same size tho. Yes we definitely wont run for long periods at WOT. We try & avoid motoring as YS8's are noisy shakey beasts but at least they are simple enough for me to work on.
cheers Paul

[Jim Cate]

& as it was a tidal install I had no time. Will be a few days before we can have another go.

That sure brings back memories of cruising in NZ where tidal grids were common. Are they still in common use there? Seem to be extinct here in Oz, which is a shame. I guess the combination of safety worriers and marina operators not wanting folks to DIY anything has overpowered the Aussie "get her done, mate" ethos.

Ahhh, progress...

Good luck with getting the prop to fit.

Jim

[Wotname]

Originally Posted by Jim Cate

That sure brings back memories of cruising in NZ where tidal grids were common. Are they still in common use there? Seem to be extinct here in Oz, which is a shame. I guess the combination of safety worriers and marina operators not wanting folks to DIY anything has overpowered the Aussie "get her done, mate" ethos.

Ahhh, progress...

Good luck with getting the prop to fit.

Jim

Plus the issue of putting in marinas where once there were none.