Propeller Shaft - broken nut - need advice

[TodBookless]

I was out sailing on Sunday, and when I dropped the sails and started up the motor to come in to the doc, there was an unhealthy banging, followed by the sound of my motor spinning very freely - but we were not moving. After docking under sail (a whole other story...), I dug into the problem and discovered a small, broken bolt lying under the propeller shaft. The shaft spins freely inside of the universal joint(? I am making up the name "universal joint" - someone needs to tell me the real name). There is a hole in the universal joint, and one in the shaft, but they do not line up. There is zero play in the shafts, so I am not sure how the bolt would ever have gone in there. The previous owner repowered the boat with an electric motor last year, so the bolt has not been in there very long. It is also a pretty small bolt that was lying down in the bottom of the boat, and it just seems like it should be bigger. I have included a picture of what I am talking about. My questions, is how are these things supposed to hook together?

 

[Loren Beach]

The shaft fits (tightly) into a coupler. It is normally locked into a fixed position by a bolt through the coupler and the shaft, or a bolt tightened down into a dimple in the shaft, or, on some boats, a keyway and key.
From the picture, I am guessing that the bolt went through. Somehow it backed out completely. Did the bolt break off and leave some behind?
More closeup inspection is needed. On our boat the bolt is torqued down and then wired to keep it in place.
Loren

 

[TodBookless]

Well, the shaft on my boat now spins pretty freely on the coupler. There are holes in the shaft and the coupler, but they don't line up. They are about half lined up and I don't know how there was ever a bolt in there. Maybe the bolt broke because they were jammed together? The bolt that I found looks like a standard, stainless steel, 1/4 inch machine screw. Is that normal? By the way, thanks for the post.

 

[Martin King]

If that shaft is spinning freely inside the coupling and is still in the
boat, count your lucky stars, cause my guess is there is nuthin'
keeping it from sliding out 'cept for the friction in your stuffing box!

Based on the photo, I'd say that the set screw broke off a while back
and the woodruff key finally bit the dust last time you were out. Find
any odd little shaped bits of metal in the bilge? You need to replace the
key and setscrew(s) and while you are at it put a little hose clamp
on the shaft between the coupler and stuffing box as a fail safe.

Martin

By the way, the setscrew is supposed to have a squarish head
thats been drilled out for safety wire.

 

[Brisdon]

From the picture it looks like your shaft went into the coupler with a key and one set screw. If the shaft is spinning in the coupler, the key is also missing from the key slot. The key stops the back and forth movement and the screw stops the in and out movement of the shaft in the coupler. If the key was left out of the assembly, the torquing of the shaft would likely shear the screw right off (if it's through the shaft), or grind a gouge all the way around the shaft (if the screw is just dimpled in). But! I want to hear about this electric motor!! You don't have to take the boat out of the water to get the shaft out of the coupler. If you split the two sides of the split coupling and work the shaft a few inches out of the boat, you can bolt a jig on to this coupler that pushes the shaft out of the coupler as you turn the screws that connect the jig to the coupler. Jig is easy to make, I've got one if you need it.

 

[gareth harris]

From your description, it sounds like the heart of the problem may be alignment - either whoever installed that electric motor did a shoddy job on the old mounts, or one of the mounts has moved. I would suggest looking at that closely before reattaching anything.

Gareth
Freyja E35 #241 1972