Drive Savers - pro or con?

[RED]

A couple of years ago I had a catastrophic failure of a Drive Saver.* I had shipped the boat across country and took the shafts out to be trued when I recommisioned the boat.* The boat had drive savers which were reinstalled at the time.* About 6 months later, one of the drive savers failed in a way that wound up bending the shaft.* After lots of reflection (and swearing), I came up with my own failure anaylsis;based in part on parts lying in the bilge.
Two primary causes of the failure were first reinstalling the drive savers with the original lock washers which I believe had collapsed.* The second was my failure to retighten the drive saver bolts after the first 10 hours of run time (as specified in the literature).* As a result, several of the bolts backed out of the unit, leaving just two until the unit shattered.

I also contacted Globe, who manufactures drive savers.* The were very helpful and went out of their way to expedite shipment of new drive savers;* they also gave me lots of helpful information, and I give their customer service great marks.

One thing I had not realized is that Globe specifies a service life of 5 years for these units, and mine were about 10 years old at the time of failure.* They also cautioned me about the need to retighten after installation.

So now my question is whether to leave them in.* The plus side, up here in the PNW, is if you hit a log, or someone mistakenly shifts at throttle, the drive savers are supposed to shatter, protecting the shaft.* The minus is if they don't shatter uniformly (like mine) the shaft can get ruined anyway.

 

[RED]

Sorry, I somehow managed to upload the photo twice.

 

[Forkliftt]

With loose fasteners the coupler would not fail as designed. Seems similar to a shear pin in my grandmothers old aircooled Wizard outboard. I would certainly consider installing them.Steve *

 

[FF]

Have never found the plastic units to be made well enough not to cause shaft vibration.

Great IDEA , waiting good construction.

FF

 

[Daddyo]

We had one but could never get the engine alignment right until we removed it and replaced with a stainless shim. No problems now but I would like to have one again to further reduce vibrations if they worked as advertised. How did your do with regard to vibration isolation? Did you ever run the boat with and with out for a fair comparison?

 

[BaltimoreLurker]

I've been considering one myself.* I would like to hear some real world results on their vibration damping ability.

FF's findings are discouraging.

 

[RED]

I haven't tried running without them. I'm doing some off season work, and the yard manager isn't very keen on them. He claims that the only real difference is alignment tolerance - tolerance specs for the drive savers is .005, while he wants at least .003 without them. My experience was that shaft vibration was somewhat reduced when I installed new ones after the failure, but that could also have been due to a good alignment job. I didn't have the experience that FF reported in that regard.

 

[Nomad Willy]

Hi all,

*** Keep the drive saver mostly because you will probably need a new prop shaft ( longer ). It dosn't make alignment easier and probably does not control vibration or deliver any extra alignment tollerance. The boat won't be any smoother or rougher. As the name implies it's a weak link and thats all. There is a number of flexable couplings on the market that give greater alignment leway, smoother operation and a fail safe link so you can still make it home. A good product ( I hate to admit it as I despise the owner ) is the PYI coupling. It may be a R@D ( of England ) product and of course I would promote seeking it there. I have used them for 10yrs and it's thumbs up. If you have quite flexable or very flexable eng mounts under a 3 or 4 cyl eng you probably NEED a flexable coupling. On the other hand if you have an eng that you can feel vibrating but can't see the eng move and have a fairly stiff hull forget the*Flexable couplings*and use a straight coupling. Having said that if you have any need for a flexable coupling and have the money I'd say get a Python Drive or an Aqua Drive. If they were free I'd say all boats should have them.

Eric Henning*

 

[Capn Chuck]

The shaft savers are not really designed to dampen vibration although they do to a lesser extent. They are designed to blow apart when the prop is fouled. They should never be left on for engine alignment. At the same time the saver is installed you should also have a shim machined to fit in its place to align the engine. If a mechanic says or tries to align the engine with the saver in place, run him off the boat. If you have a vibration problem you either have a bent shaft, damaged prop or the engine needs alighnment, so those need to be fixed.

-- Edited by Capn Chuck at 20:04, 2009-02-03

 

[RED]

Chuck
You are right on about alignment. My mechanic also says the procedure is to align the shaft
couplings without the drive savers, and then back the shaft out just enough to install the (If I
decide to reinstall them).
I just found the original literature from the manufacturer, which interestingly does not say anything about coming apart. Their only claim is "absorbs thrust and torque from the propellor shaft, as well as excessive shock from changing gears and high speed planing. t also helps control damage from torsonial engine movement."
"Absorbs Shock; Absorbs Vibration, reducing noise, Prevents electrolysis" are the claims fron the brochure.
It also says that it "keeps working for the life of the drive train", which is the opposite of what the service tech told me when I ordered replacements.
So I had some misinformation, and they are not designed to blow apart, at least not according to the mfg.
So my current plan is to have the shafts aligned without the drive savers, and I think I will do some trials with and without them.

 

[Capn Chuck]

Red. When ever I have had to deal with the prop savers the shaft needed to be replaced if deciding to remove them. Once installed the shaft should be too short with the drive saver off. You absolutely don't need one. This is one of those owner preference things.

 

[Phuket]

Capn Chuck is right in that it is generally not possible just to remove the drivesaver due to shaft length.* If the shaft were long enough to do this then then overhang at the prop past the rear strut would be excessive and possibly lead to flexing and or vibration.* I have seen people remove them and replace them with a machined steel piece the same dimensions as the drivesaver -* it can be convenient to make up a piece like this to use for engine alignment.*
Cheers, Leon.