Propeller shaft came out of transmission

Ross · Jun 2, 2009

If the gear case isn't broken then the rebuild should be less than a new unit. It could be done in less than a week if yours was the only one.

Manny · Jun 2, 2009

That seems like an odd failure... What type of transmission is it? I would contact the manufacturer and let them know what happened. Might not hurt to talk to your insurance company also. Depending on the design its possible the case cracked where the shaft is supported. Did you get a line wrapped around the prop or some other similar event?

Manny

Mike Holibar · Jun 3, 2009

From the photo it looks like you have no flexible coupling. This would be unusual if your engine sits on resilient mounts and may be the reason for the failure. If you have reasonable access you could try undoing the four coupling bolts and seperating the halves. Inside I am pretty sure you will find the nut has come off the end of the transmission output shaft. Repair maybe as simple as obtaining a new locking washer and then refitting the coupling and doing up the nut to the specified torque, assuming the seal hasn't been damaged. Because the shaft is supported by the stern tube and strut etc, it should have stayed in alignment and not have damaged the seal as it came out. Hopefully the spline is undamaged also and the coupling should slide back in fairly easily.Once the coupling is refitted to the trans, I would be fitting a flexible coupling between it and the shaft. It shouldn't take you more than an hour or two to try refitting the coupling and it could well be that that will be the end of it. Worth a try before the more expensive options. I does strike me as rather odd that a large modern yacht such as yours wouldn't have orginally been equipped with a flexible coupling.
Good Luck,

Mike Holibar · Jun 3, 2009

As an aside I have had two occasions where prop shafts have come out of couplings. One was a few years ago on a Hereshoff H28 and was caused by the lack of a flexible coupling. The consequenses were minor, loss of power on a calm evening about a mile from the anchorage. I just pushed her in with the dinghy. The other was more expensive. We left the mooring to recover the dinghy which had come away. To get away quickly I put her full astern and woops - no one home. Lees sure, anchor over. helm over, forereached clear of the shore but "T-boned" my neighbour before the anchor coulf stop us. I would be doubt we were doing more than half a knot but we stove in lifelines and toe rails on the other boat before we could stop. Fyne Spirit has a flexible coupling but the shaft half was not correctly fitted and the astern power was enough to pull it out. Needless to say it is well secured now.

Maine Sail · Jun 3, 2009

Mike Holibar said:
I does strike me as rather odd that a large modern yacht such as yours wouldn't have orginally been equipped with a flexible coupling.
Good Luck,

Mike,

In the US flexible couplings are actually quite rare and mostly an aftermarket item unless the owner specifically asked for one during the build or added one after the fact Having been on a lot of boats over the years I would guess that boats with flexible couplings make up less than 5% in the US. Also on many older boats or boats with v-drives flexible couplings just don't fit. The don't fit my bot either..

I can't say I have ever seen a failure like that one so don't know what to say. You might look up the exploded parts diagram and try to figure out what may have failed and also consult the manufacturer..

Don12364 · Jun 3, 2009

Hi,
We are all now critically interested to know what goes on inside our (read 'my') gearboxes.
Anyone have, or could point us to, an exploded diagram of the Yanmar gearbox.
I think it is a Kanzaki-Hurth KBW10.
Regards

Tim R. · Jun 3, 2009

I agree with Mike that the shaft is still intact and it is just the coupling that has come loose. A rebuild is certainly in order if you ran it after all the fluid leaked out beyond the seal.

kloudie1 · Jun 3, 2009

Ohhh, not good.. Like Tim and Mike said, I think what we are looking at is the spline that drives the coupling on the output shaft. The nut that holds the coupling on, has come off and allowed the reverse thrust to pull the coupling off the output shaft. The oil seal rides on the coupling neck, so when the coupling backed out, the oil had a big hole to run out of.. If you are lucky and didn’t run it too long, the case can be cleaned out and flushed and the coupling and seal re-installed and all will be good.. CAUTION! If the shop isn’t honest, they will reinstall the coupling half and oil seal and charge you for a full rebuild.. If ya have a gear head friend, ya might get him to carefully talk to them about the problem and watch the work..??

kloudie1 · Jun 3, 2009

In most of the Kanzaki boxes, the thrust bearing is held by the shoulder on the neck of the coupling half. When the coupling locknut came off, the shaft may have moved aft a little. If it was operated that way for a “while” (grinding noises and lots of heat) there may be damage to the shift selector and thrust bearing.. Again, Those can be checked easily .. The oil that is in the box will tell an interesting story. Again, it may be as simple as a new locknut and o-ring and oil seal.. Best to ya.

Mike Holibar · Jun 3, 2009

Don't panic. The I overhauled the kanzaki box on my Rasmus last year. In the hands of the po she had at some time filled up with water and had been run for some an unknown time in that state. When I bought here I flushed it out and used her for a season. Then stripped it down and replaced the bearings, tapered roller type, which showed some minor pitting. While I was at it I changed the ratio to 2.6:1 to get the engine matched to the prop or vice versa. On the F39 which has a Hurth gearbox I was horrified to find no oil at all. I had checked and topped up the oil at purchase time but, unknown to me, she had blown the seal on the selector shaft and had I suspect immediately pumped all the oil out. I suspect we probaby motored for more than 300 miles in that state and it was only when changing gear became difficult that I spotted the problem. Replaced seal and refilled - no further problems. There must have been just enough oil (ATF) to keep it lubed. Also, the load on the thrust bearing is not that high compared to the capability of the bearing. We once calculated a 42HP launch set up would genrste less than 2000lbs of thrust, so I would expect a 30hp yacht is going to be something less than 1500lbs.
Claude, very interesting your comment re flexible couplings. Does this mean that engines are usually solid mounted? Must be hard on stern glands with soft rubber mounts and rigid shaft.

Witzend · Jun 5, 2009

I feel your pain, right in the middle of sailing season. Seems like it should be designed to unbolt the transmission from the engine and not have to remove the entire engine?
Can the engine be chocked up at such an angle to alow the removal of the transmission?

Joseph Shirley · Jun 7, 2009

Mainsail was correct in that most couplings are not flex types. Additionally your transmission problem and your shaft backing out are separate problems. I won't speculate about your transmission problems but it appears that your shaft was inserted into your coupling without a key in a keyway (although it could have had a loose fitting key) and only a setscrew in a detent which wasn't safety wired to prevent it from vibrating loose. It would appear that your set screw vibrated almost out of the detent and was held in place by the thrust pressure of the shaft against the coupling (or by the key if it was there) and when you shifted to reverse the pull on the shaft just yanked the shaft out.
The set screw in the coupling normally has little holes drilled through the head expressly for lock wire which you appear not to have had.

Good Luck

Joe S

Propeller shaft came out of transmission

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