Shaft Savers

[millennium]

Installed in the shaft coupling, they are suppose to shear if the prop hits something.

Opinions on them??

Does anyone know:

Is it ok to align the shaft with the saver installed?

Should the couplings be connected with a jumper wire for electroloysis.

Thanks. Bill

Waiting on the Hudson for the Champlain Canal to open. 3 weeks now$$.


-- Edited by millennium on Friday 27th of May 2011 09:57:08 AM

 

[jleonard]

I discussed this with my marina several years ago when the repower engine installers put the new engine 1 inch too far forward. I needed to add 1 inch to the prop shaft to make room for a zinc.

They said if I do install one to buy 2 of them because they had seen many failures and I would need one aboard.

With that knowledge I had a 1 inch thick steel spacer made. Never had a problem.

 

[Nomad Willy]

I've run one that I got from Hamilton Marine in Seattle and all went well. I've heard that failures are rare but some products have a fail-safe system. I have plastic (polymer) engine mounts and consider them a high quality product. They (PolyFlex) have plastic disc couplings also . See**** http//www.polyflex.com.au

 

[FF]

You do the line yp without them , then slide the shaft back.

Purchase a pair as the units frequently are poorly made and will add vibration to some instalations.

 

[RED]

Here is what happens when a drive saver failed.* This occurred shoertly after I recomissioned the boat when we purchased it.* As you can see, it did not fail completely, and the shaft was held by a single bolt, resulting in the shaft turning in a wild eccentric, which destroyed the shaft.* In my post failure analysis, this was the result of several issues.* I was concerned that the shafts might have been bent in overland transport and they were removed to have them checked.* When they were replaced, the yard re-used the old bolts and lock washers, and I think the washers had collapsed.* The globe drivesaver company gave me excellent service and advice, overnighting replacements to me.* They also advised me that drive savers have a limited service life and must be replaced on a regular schedule, which I was unaware of, and these were obviously past their service life.

*

 

[Nomad Willy]

RED,

I'll bet almost all the failures of these Shaft Savers is the result of people running them intentionally or otherwise as a vibration damper** ...and of course they are not. I see split washers and it looks like they did'nt fail (at least 3) and the bolts are too short. Split washers can break and then you've got nothing. Ideally the bolt head should be fwd and the bolts should be long enough that at least half a nut height sticks out beyond the nut. If the whole system is aligned and the engine mounts are in good shape these shaft savers should perform well.

 

[RED]

Eric
My picture didn't capture everything. After the event, I found two of the bolts in the bilge, which suggested to me that they had backed out. I was not (attempting) to use the drive savers as vibration dampers; I had trued the shafts, and had the shafts aligned at the yard. I understand your comment about having a bolt long enough, but that cannot be the case with drive savers, since the bolts go blind into the drive saver - they are not through bolted, by design.

I wasn't trying to disparage drive savers; in fact I installed new ones. For me, there are at least two "take aways" from this failure.

Drive savers have a limited service life (5 years max per the manufacturer).

Never reuse bolts and lock washers in a high vibration environment.

A couple of other thoughts: part of the engine room check should be the drive shaft fastening (particularly if you have drive savers).

An open question: does anyone use drilled and wired fasterners on the drive shaft?

 

[millennium]

Safety wiring coupling bolts: I don't, probably a good idea. I use lock washers for whatever good they do.

How about a wire jumping the drive saver to reduce electrolosis? If the prop and shaft are not in contact with any other metel ( drive saver and cutlass bearing) will they be subjected to stray electrical currents?

Incidentily, I hit a rock in the SC ICW rockpile, the drive saver did nothing. prop damaged and keyway broke. Maybe not enough force to shear the drivesaver.

 

[Nomad Willy]

If you want a good flexible coupling consider the PYI flexible coupling. I despise the owner and think he owe's me a rebuilt gear. Make sure the bolt heads don't touch the gear flange or it will hammer the thrust bearing and probably do damage. As power is increased the plastic discs flex and if you don't have the right coupling for the thrust of your engine the bolt heads will hammer the gear. But if you get one strong enough it seems to be a good coupling. I think it's made in England and sold by PYI. I think ther'es a better flex coupling made now***** .....anybody have knowledge of same?

I did a search and here's the product line that probably is better than the PYI that is actually an R&D product.
<table style="width:100%;" border="0" cellspacing="6" cellpadding="0"><tbody><tr><td align="center" valign="top" width="100%">

</td></tr><tr><td align="center" valign="top" width="100%">12 Moran Drive #4, Rockland ME 04841 USA | 207 593 9009
info@evolutionmarine.com</td></tr><tr><td align="center" valign="top" width="100%"></td></tr></tbody></table>
The coupling pictured is not the one I refer to. Did'nt expect the picture. See flexible couplings on thier home page.




-- Edited by nomadwilly on Monday 30th of May 2011 11:12:11 PM

 

[GregJ]

RED wrote:

Here is what happens when a drive saver failed.* This occurred shoertly after I recomissioned the boat when we purchased it.* As you can see, it did not fail completely, and the shaft was held by a single bolt, resulting in the shaft turning in a wild eccentric, which destroyed the shaft.* In my post failure analysis, this was the result of several issues.* I was concerned that the shafts might have been bent in overland transport and they were removed to have them checked.* When they were replaced, the yard re-used the old bolts and lock washers, and I think the washers had collapsed.* The globe drivesaver company gave me excellent service and advice, overnighting replacements to me.* They also advised me that drive savers have a limited service life and must be replaced on a regular schedule, which I was unaware of, and these were obviously past their service life.

*

*I have come back and looked at this post every day since it was posted trying to work out how a vibration damper, and that is strictly what it is, can be called a shaft saver.*

The very design of the thing screams that it will destroy the shaft if it strikes something hard enough to make the "drivesaver" let go by forcing the bolt section on the shaft flange to be forced away and over the bolt section on the transmission output flange, thereby bending the shaft sufficiently to cause*it to be unuseable.

After many hours studying the pic, I believe it was caused by being part of an incorrect mounting system, ie, the engine is soft mounted and the shaft is also soft mounted, add them to a flexible coupling as used in the pic here and you will destroy the couplling and shaft again probably well within the 5 years quoted, pick up some weed or light rope on one blade of the prop and that will set up a vibration trying to force the shaft to wobble at the transmission end, which will pressure the soft coupling and engine/transmission into performing wild figure eights due to having the 3 soft mounts.*

If the soft coupling is left out and the shaft is correctly aligned to the output flange, there really is no need for the soft coupling.*

If you feel a drive saver is really needed, then remove the grub screw from the shaft coupling, have a bronze or aluminium disc made and placed between the grubscrew and shaft, then remove the pin with*the split pin in it and replace the pin with an aluminium or other softer material with preferably a groove and C- clip to retain it rather than the split pin idea, reduces the number of places where it is possible*to damage your hands in the engine room.* If the prop strikes something, the shaft will break the pin then there will be sufficient friction left to supply reduced power to reach home or safety so one of the spare pins you had made when having the original soft pin made, can be fitted in calm water.

Edited to correct speeling mistakes

-- Edited by GregJ on Tuesday 7th of June 2011 10:10:04 PM


-- Edited by GregJ on Tuesday 7th of June 2011 10:12:38 PM