John,
The reason the plastic "thrust washer" looks eaten away is that it is not
intended to be a thrust washer.
Neither it or the strut are intended or designed to take thrust loads.
Your best bet is to take it to a yard that knows their stuff, and see what they
recommend. That or a marine engine specialist. They will be able to recommend
any of a number of aftermarket thrust bearing setups that can be installed, if
somewhat painfully....

Steve

what happens in reverse?

"john m." wrote in message
m...
Thank you guys for the replies.
There is one problem. The propeller shaft has a roller chain coupling
that connects it to the hydraulic drive. I think that this type of
coupling does not take any axial load too well. The only place left to
take the axial load is the strut in front of the impeller. When I look
at the plastic washer I can see where the axial load eats away at the
plastic thrust washer. That is why I was thinking to replace the
plastic thrust washer with something more robust.

barry lawson says:

what happens in reverse?

Heehee..... I hadn't even thought about that. Good question.

;-)

Opps! Been there done that!

Once had the shaft spin out of the coupling while in reverse.. It even
cleared the packing box but jammed against the rudder..

Took on some water until I could warp myself back into the dock and drive a
plug into the packing box..

Later had a diver push the shaft back in, knocking the plug out.

Since then I have always had a through bolt or pin in additions to the set
scews.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions

"barry lawson" wrote in message . au...
what happens in reverse?

"john m." wrote in message
m...
Thank you guys for the replies.
There is one problem. The propeller shaft has a roller chain coupling
that connects it to the hydraulic drive. I think that this type of
coupling does not take any axial load too well. The only place left to
take the axial load is the strut in front of the impeller. When I look
at the plastic washer I can see where the axial load eats away at the
plastic thrust washer. That is why I was thinking to replace the
plastic thrust washer with something more robust.

I have a folding prop, so in reverse its very slow. It also makes a
funny noise when the shaft pulls on the roller chain coupling, but so
far I never had a problem with it.

This whole installation sounds 'Rub Goldberg' and I can't imagine any
professional builder or boat yard doing such an installation where there is
no proper thrust bearing.

As I stated earlier in this thread, I suspect someone, in the past, has
replaced the OEM hydraulic drive motor with this chain drive system.

I find no fault with the chain drive if there is no way to get a hydraulic
motor down into the space. It's hard to say without seeing the
installation..

However, to salvage this installation, I would recommend putting a thrust
bearing on the forward (inboard) end of the shaft and the bearing should be
mounted to some substantial member in the bilge. This would have to be
glassed in and should be able to absorb both the forward and reverse thrust
of the shaft.

Even though the engine is only 15hp the thrust is not to be taken lightly
(literally). If it move the boat, then there is a mechanical force against
the hull or in this case, the strut, IMHO.

Steve
s/v Good Intentions

John,

Yes, I was contracted to repair the strut bedding when the boat got run
with a damaged blade. That boat did not have the couple you describe
between the hydralic motor and the prop shaft. There was also no
conventional stuffing box. The prop shaft is enclosed in the stern tube
from the after end of the strut into the hydralic motor. The motor is
actually attached tot he stern tube and is supported by both that and a
torque brace.

After we got all of the other stuff fixed, the boat still would not make
more than 4 knots and the engine was not loading. It back like a mad
man. So the owner got another set of blades for the other rotation and
shifted the pump to astern for ahead and now makes hull speed just fine.
When I talked to him last he was trying to find someone that knew how
to overhaul the pump and motor. When I see him next, I will ask him.

A chain coupling in a drive shaft is rare and not a proper application.
There is no way to put an axial load bearing (thrust) inside the stern
tube, so it must be in the hydraulic motor. That is part of why the
plastic washer is both installed and torn up. I suspect the washer is
required to keep the coupling halves from wearing on each other.

It is, however, not costing you horsepower. Bearings going bad can
cause vibration and failures, but if they eat horsepower they burn up
real fast. I suspect that if you are short on boat speed as you seem to
say farther down the thread, you have hydraulic drive problems just like
the Scampi I know had (may still).

I would see about getting both the pump and motor looked at before you
invest much effort in other paths.

Good Luck

Matt Colie - See Prior Sig

john m. wrote:

"Steve" wrote in message ...

To me, this is a bit confusing??

Does your boat have an inboard engine with a propellor shaft?? or are you
talking about an Outboard motor or Out drive??

A properly installed marine engine will have the thrust bearing in the
reduction/reverse gear. If it is an OB or Out Drive, the thrust bearing is
inside the lower unit. I've never heard of a thrust bearing at the
propellor. There should only be a water lubricated cutlass bearing.

Please provide more information on what you have, engine/rev. gear, etc. and
maybe we can figure a solution.

Steve
s/v Good Intentions


Here is a link that shows a diagram of the boat
http://home.worldonline.dk/sejler/scampi/scampi.htm
This boat has an hydraulic drive system. The brace that you see in
front of the impeller is where the bearing should be ( I think) It
looks like a very strong support made out of metal and imbedded in the
fiberglass.