Drivesaver - Good or Bad ?

[pcmm]

Originally Posted by David M

I used to use them. They destroyed themselves too easily making for an unreliable drive train.

You used to use what? drivesavers? AquaDrives? how did they destroy themselves? ( other than in the way they are supposed to?)

[a64pilot]

I'm looking for something to absorb / dampen drive line vib.
Above about 2500 or so I pick up a resonance vibe that results in shaft whip, I cannot figure it out, It's aligned as close as I can get it, within a couple of thou at most, new engine mounts and new cutlass bearing.
It does not vibrate in reverse, or I don't think it does anyway, just forward, and once the vibe starts, it gets bad, fast, only way to stop it is to reduce RPM immediately.

[fryewe]

Never had such a resonance, but...

...one thing I might try if I had a resonance would be to clamp a zinc or two along the length of the shaft to try to change the its harmonic balance. You could slide them around a bit to alter the effects.

I have room and access to do that. Not everyone would.

[a64pilot]

I've got all kinds of room to clamp a zinc, and being a former Helicopter test pilot, am familar with harmonic resonance, too familar.
Your idea has merit and would be easy and cheap to try, I'll give it a go.

I'm afraid that maybe the Autoprop is my source of vibration, an Island Packet of mine's vintage has an enormous amount of dead wood, I'm afraid that maybe the difference in water flow from behind the dead wood and out in the open may be causing the prop to change pitch, and induce a vibration?

[botanybay]

I have used both the drive saver and the aqua drive systems on my boats.

Both work well, the drive saver does result in a need to ensure the bore alignment is maintained. I used a dial indicator on the prop shaft during installation to make sure the shaft was centered.

The big advantage vs being directly coupled is if you have a longer prop shaft the movement of the engine at sea causes less vibration.

Definitely carry coupling bolts and nuts in case something goes wrong.

This was on a 4-107 with a v-drive

The new boat has an aqua drive system and it is vibration free. The units are not maintenence free, they do need rebuilt on a schedule, in my case it was easier to replace the CV joint and the thrust bearing.

What is nice is that the transmission does not see any forward and aft loads as these loads are carried on the thrust bearing soft mounted to a hard point on the boat.

This allows much softer motor mounts and less vibration.

The aqua drive unit is on a 90 hp Perkins driving a 55 foot sailboat.

Sent from my SM-G935V using Cruisers Sailing Forum mobile app

[Squanderbucks]

Squander Bucks is a 38 ft twin diesel power boat. I installed Drivesavers on it back in 1999 or 2000. Twice they have saved my transmission. The first instance was returning from offshore through St. Lucie Inlet near Stuart Florida which has shifting bars along the channel. Hugging the Eastern edge during a high traffic time I hit bottom at 20 mph with the starboard prop. The Drivesaver worked as designed and the shaft was not bent and the transmission survived without any damage.
Second time was in 2004 when approaching Freeport Bahamas in about 3000 ft of water at full cruise of 23 mph and hit a submerged shipping crate directly off the mouth of the commercial port. Sounded like a bomb went off. In this case the shaft was not bent but prop needed pretty extensive work. The transmission gears and seals were ok but the auxillary mounted pump did get hit by a piece of the shrapnel from the exploding Drivesaver and had to be replaced. Also the engine had to be re-aligned as the engine was shifted in the bunks.
I carry a spare Drivesaver on board and had my local machine shop make up an aluminum "blank" that could be bolted in place to allow motoring home at a slow pace if needed.
Have not found that they do much for alignment purposes. Tried it both ways but now check alignment with Drivesaver off the put it back on before completing the alignment process.
Definitely in favor of these or at least something like it .

[NoTies]

A lot of the problems with any flexible coupling, regardless of brand, are when they are fitted to drive trains that have only one shaft bearing and flexible engine mounts. There is nothing to hold the forard end of the shaft centred exactly with the gearbox output flange so radial runout can lead to vibration and premature coupling failure, even if perfectly aligned.