Tmacmi

Propeller Shaft Fore/Aft play

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I am working my way through the list of items that must be done while the boat is on the hard. Next item. Propeller shaft and stuffing box.

When I first got it, there was a "singing" sound coming up the shaft at a specific band width of RPM. It was like the resonance you get when running a wet finger around the rim of a glass. Ultimately it disappeared, except under heavy load of people or a strong stern wave.

There was also a good bit of water coming out of the stuffing box under power. It was just about one large drop coming out per second. Its dry at standstill.

When I hauled it I found the wear mark shown in the photo below. The shaft moves back and forth into the boat by the distance of that wear mark by hand. There is no side to side play in the cutlass bearing.

https://imgur.com/oJrDPaD

When I went inside I found this condition. I'm not sure you can see it clearly, but the red line is pointing to where a wire has broken. I am not entirely certain what the wire is there for, but it appears that the back and forth motion of the shaft sheared it. Interestingly the wire goes through the shaft key as well as the set screw.

https://imgur.com/pCj7KgP

As you can see in this photo the set screw doesn't appear to have come loose.

https://imgur.com/c99DMXH

I don't know if the cause might be a propeller change. The PO told me he changed the propeller from a 2 blade, with details shown below to a three blade (I couldn't get details of the 3 blade because its mounted.) The motor is a Yanmar 2qm15. It has a Kanzaki transmission showing a 2.14 gear ratio. I know the gear ration has some interplay with propellers but I don't know details. Up to this point I thought I had to simply restuff the stuffing box. But I'm guessing I have something more than that.

https://imgur.com/zHL9PLe

Thoughts?

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3 minutes ago, Diamond Jim said:

I'm trying not to visualize propeller shaft foreplay.

I figured it would get attention if worded that way.

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You caught this disaster in the nick of time.

That wire is a seizing wire. It's there to prevent those square head bolts from coming loose. Those square head bolts are set screws. They should be tightened into dimples in your prop shaft; together they stop your shaft from walking out of the coupling when you're sailing or, more importantly, when operating with astern propulsion.

Somehow, your dimples and/or set screws are fucked and that's allowing fore-and-aft movement of the shaft. In forward, that's not a problem as the thrust shoves the shaft into the coupler. In reverse, it can allow the shaft to walk aft out of the coupling, out of the boat and leave a gapping hole while the still-rotating prop cuts your rudder to ribbons.

You'll likely need to do most of the following:

  • Remove your prop
  • Remove your shaft from the coupling
  • Remove the coupling from the transmission
  • Remove your shaft, which may mean dropping the rudder
  • Take the coupling and shaft to a machine/prop shop and have them evaluate whether the dimples are damaged beyond repair; whether new dimples and keyway could be cut; renew the locking screws; square the flange, etc.

In order to provide them with the information necessary to do all this - be sure you carefully document the distance from your strut to your prop so they can understand whether they can shorted your shaft a bit to accommodate any repairs to the shaft. One strategy for saving the shaft is to install a shaft-saver (a hard rubber hockey-puck size thing) between the engine and the coupling, which has the effect to lengthening the shaft by about 1" and allows 1" of shaft to be cut off while maintaining strut-to-prop clearance, which should be only about 1/2 the shaft diameter.

Once you get your head around the amount of effort and money involved, you might find yourself wishing you'd left it all as-is, and that the boat sunk when it finally failed for good.

 

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The fit on your coupling and shaft is probably toast.  A machine shop can take the shaft down a little and bore/broach a new coupling for a proper fit.  Shouldn't be that bad $$.  

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Well, it looks like I have some work to do. 
 

couple questions:

1) is it possible to back the shaft out, bore the dimple in the shaft deeper and reset the screw deeper?

2) do you have any good resources for dropping the rudder from a wheel controlled boat.

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There are lots of maybe patches you could do, the most secure solution would be to bring the shaft back in to the correct position and drill through the set screw hole all the way through the shaft and coupling. Then through bolt with a castle nut and cotter pin.  This can be done safely in the water  and keeps your shaft secure but does nothing to deal with the slop between the coupling and shaft.  If you have any out of water pics most yards can quote you on a proper repair. New prop shafts are not even that expensive in the grand scheme of things.

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No. Do not drill through your shaft. Do not thru bolt a pin. Do not repair in place. Every prop shaft uses a key, set screws and dimples for a reason.

Dropping your rudder is somewhere between trivial and a lifetime project ... Removing the quadrant is the easiest part, probably four machine bolts. Dropping the rudder depends on the boat, which you haven't explained. Bearings and retaining details are many and varied.

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36 minutes ago, Moonduster said:

No. Do not drill through your shaft. Do not thru bolt a pin. Do not repair in place. Every prop shaft uses a key, set screws and dimples for a reason.

Dropping your rudder is somewhere between trivial and a lifetime project ... Removing the quadrant is the easiest part, probably four machine bolts. Dropping the rudder depends on the boat, which you haven't explained. Bearings and retaining details are many and varied.

The extent of the repair you effect really depends on what your intended use of the boat is before you haul out.  If I was dealing with your issue I would drill it and bolt it, with the understanding that both coupling and shaft eventually need to be renewed.  When the tolarances are toast the keyway setscrew or screws are useless.  Everything in this arrangement is dependent on the other parts, the keyway is supposed to take the rotational load of the shaft the set screw one of probably two set at 90 deg is used to retain the shaft in a fore aft position and take the fore aft thrust load.  All of these are dependant on on the tolarances of the coupling to the shaft.  If the shaft is freely floating in the coupling the shaft and the coupling are out of tolarances.  Renewal of set screws or dimpling the shaft will be a ineffective patch.  

But above all go talk to a yard or prop shop.  Unless you have the ability to effect repairs yourself you will be dependent on local venders to get you going, someone on a forum telling you it only should cost x dollars doesn't mean alot in the real world.

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Im going to guess the fore aft movement is bad/missing set screws and pooched keyway. Does your rudder need to come out to get it fixed? mine is slighty offset to allow such a repair. The coupler clearance may be just fine. You can start the process in the water, you can remove the set screws, square bolts and pull the shaft back enough to get a caliper on the shaft and the internal coupler and see if they are too loose, put it back together putting the screws back in place and reintall the seizing wire. Maybe it just all came loose and needs a reset.

But please do not drill through the shaft, when you do that you have created a shear pin. It weakens the connection and the shaft and when it F's up you have a really big mess. 

usually there is a zinc annode or similar in front of the strut that will prevent a complete backout of the shaft , but thats not a thing I'd bet on

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The boat is out of the water. It has a spade rudder with a radial cable drive steering. I’ll have to figure out that process.

This weekend I’ll loosen the shaft from the coupler pull it back and see what is in there.

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If you are out already no reason not to get it done right.  A good yard will will give you direction without emptying your pockets as long as they get some work.

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10 hours ago, SASSAFRASS said:

If you are out already no reason not to get it done right.  A good yard will will give you direction without emptying your pockets as long as they get some work.

I think I may have found the right guy. Someone to help with middle steps without charging, knowing he's going to get some larger work out of it if there is some.

Saturday I'm going to undo the set screw and see what the condition of the shaft is once I pull it back. I'll take a bunch of photos and proceed in increments.

 

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Or you could tighten up the retaing bolts to see if the shaft still moves. If the shaft doesn't move fore and aft then put a "4 sale" on it. Get the boat you really want. Or sail it. Your choice... 

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The coupling to shaft is supposed to be a light press/interference fit. Yours has been moving in / out of the coupling and that that critical tolerance has likely been lost. Keep this up and they key will eventually fail, or the shaft and the shaft can literally come out of the coupling.

A machine shop can fix this for you but they need the shaft and coupling...

Shaft to Coupling Fit & Face

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Not uncommon for boats to have offset struts that allow pulling the shaft w/o dropping the rudder.  Hopefully yours is setup this way.  Cheers

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Are you sure that the shaft is moving in the coupling?

Could it be bad motor mounts allowing the whole shebang to move?

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Worst case scenario is if the whole coupling moves in relation to the engine block - this means a shot thrust bearing and a bottom end rebuild of the engine

Having said that, straightforward wear of the shaft / coupling connections seems to be the most obvious

Any progress by now?

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