Shaft Coupling Spacer

[snook91901]

When I installed and aligned my A4, I had the prop shaft pulled too far forward to accommodate a shaft zinc. I would like to push the prop shaft back with having to move the engine. My plan is to put a spacer between the coupling to give me that extra inch that I need.

I've seen rubber coupling spacers on boats before. They're basically just flat cylinders of rubber that sit between the engine and prop shaft couplings. I think they are marketed for reducing vibration and side loads on bearings. My problem now is that I can't find the things anywhere. Can anybody help me out? What is the name for this item and who sells them?

[snook91901]

Also, what is the OD of the coupling and the bolt size.

I'm too far away from the boat to measure.

David

[hanleyclifford]

The device you mention is called the "Drivesaver." They are marketed as sacrifice couplings and to isolate the engine from the shaft electrically.http://www.henrysmith.com/globedrivesavers.htm

[CalebD]

Drive saver for A4 direct drive setup

I actually have one of these that I got from another boater. I think I paid $100 for it. It is "slightly" used but seems in good condition. I'd be happy to part with it if you want it. You will appreciate the "used" price after you look at how much new ones cost. PM me if interested.

I had the same issue with the standard 1" collar zinc not fitting between my prop and hull (no strut). We did a shaft replacement on our boat and I had the prop shop add about 3/4" to the length of our new shaft so now I can easily fit a 1" collar zinc without using the drivesaver.

BTW, I think you will only gain about 3/4" of shaft length with the drivesaver.

[snook91901]

Is it possible to run the same 3 bolts through both couplings and thereby connect the prop shaft and the engine electrically with one of these things?

[sastanley]

Snook...have you thought about a zinc on the end of the shaft..like a prop nut zinc?

[tenders]

What do these do that a piece of Starboard plastic or a cut-down hockey puck don't do?

[ArtJ]

I would wonder if a hockey puck or other substitute would have the
proper shear strength? Maybe some of the Mechanical types can chime in?

Regards

[tenders]

My thinking is that like the fiberglass layers and balsa core of a deck the strength needs to be in the fasteners and boundaries of the setup; the stuff in the middle is not really critical. As long as the "core" is sufficiently rigid and the fasteners are tight, a spacer made of relatively simple and cheap stuff would do its job absorbing vibration and allowing the fasteners to shear when the prop hits something.

What am I missing?

[CalebD]

Is it possible to run the same 3 bolts through both couplings and thereby connect the prop shaft and the engine electrically with one of these things?

Looking at the drivesaver contraption I believe that it electrically isolates the shaft from the engine as there are 6 bolt/nut connections to the 'plastic' donut (3 for output flange, 3 for shaft coupling).
That should not stop you from adding a wire (or two) that will connect the two sides.
I believe you are supposed to wire the coupling and set screw anyway, so it wont back out.

I don't see why you couldn't make your own with something like G10 or Starboard. The drivesaver unit I have is theoretically designed by an engineer for this application so you shouldn't have to worry about shear strength.

This is the model 353 for A4 direct drive: http://www.getaprop.com/content-prod...saver_353.html

[CalebD]

Snook...have you thought about a zinc on the end of the shaft..like a prop nut zinc?

I looked into this idea as well on my old shaft. Apparently there are (at least) 2 different methods used for holding a propeller on the shaft.
The set up I had with my old bronze shaft used a single Castle nut with a cotter pin to secure it. With this set up there is no zinc (that I could find) that would fit over the Castle nut.

The set up I had fabricated with my new SS shaft at the urging of my prop specialist has a longer amount of thread and the prop is held on by 2 bolts locked together and a cotter pin. They sell a more expensive zinc with a nut embedded in it which I can use for the locking nut now that I have the threads for it.

Since I also had my shaft lengthened by 3/4" I now have space for the cheaper 1" collar zinc. I bet you can guess which zinc I'm using now.

[snook91901]

I haven't thought about a prop nut zinc, because the prop nut I had(it disappeared last week) was completely smooth and round. To the point that I thought I had some kind of unique prop shaft set up with no threaded end. As a temporary measure I put my collar zinc over this part of the shaft, and I am guessing the extra inertia on it was enough to loosen it up at some point when the shaft was accelerating in forward. (wishing there was a d'oh emoticon)

Given their price, I think buying a used drivesaver and sticking with cheap collar zincs might be the cheaper, but probably not easier, option.

[CalebD]

Snook,
If you can get 2 nuts onto the threads of the end your shaft then you should be able to use the prop nut zinc option.
I lied though, even with the 2 locking nuts I have a cotter pin as shown in the pic I posted above.

I have very little clearance of my rudder in the aperture for my prop, plus I had just bought a new collar zinc which finally fits!!! With my old shaft I had maybe 3/4" between the prop and deadwood to fit a zinc. It was such a PITA to grind down a 1" zinc to around 5/8" thick to get it to fit. Anyone need a 5/8" thick collar zinc that I had milled down from 1"?

[edwardc]

Caleb,

With that collar up so close to the deadwood, I would worry about restricting water flow to the cutless bearing.

[CalebD]

Thanks Edward,

That is a concern of course.
I unscrewed the packing nut while in the water and I do get water dripping out of the stuffing box base - perhaps 2 drips a second (new shaft, new cutless etc.).
I am currently monitoring the stuffing box and backing off on the packing nut to get the amount of drips working properly as it was just re-packed.