Prop shaft slipped off transmission when in fwd gear

[gonesail]

we had some shaft play in our coupler. had to pull the shaft to see that it was damaged as well. so we needed a new shaft and coupler to make things right. there are huge forces exerted on the drive shaft and the prop shop said that no amount of welding can fix it

[Scubaseas]

Originally Posted by OS2Dude

A propeller driving the boat forward can not come out. I have heard of it happening when a boat is in reverse. If your shaft was not engaged, then the forward speed provided by the sails seems to have been enough to do it, but that means your shaft is WAY TOO LOOSE in your collar. Collars will corrode and will lose material over time. It seems a new collar is in your near future. . . You may also want to check the alignment of the shaft and the engine. If it is off even a little bit, it can cause issues like this.

I am not familiar with the split collar referred to in previous posts, so I don't know how they are installed or balanced. We had to replace our shaft &collar last summer. We were advised to have any shaft (new or old) machined along with the collar to match.
The replacements we ordered were machined to very tight tolerances, closer than you would be able to do on board. (Tight enough that the shaft had to be tapped into the collar from outside.)

NOTE: The matching flange on the transmission is an INTRGRAL part of the transmission. If it is damaged in ANY way the entire transmission will need to be replaced.

I disagree with some of this. A prop shaft can come out in neutral. I bet it could come out in drive if the waves were steep enough.

I did not know that the output flange was not replaceable (it is) and the whole gear box would have to be replaced. Any decent machine shop could true up an output flange. Most gear boxes the output flange is held onto the shaft by a nut and is easily replaced. Change the seal while you're at it.

I would question the need to balance a 1.25" shaft (if even that much) spinning at less than 1500rpm. There is usually a reduction gear (2:1 or 2.45:1 or 2.6:1.

If you heat the coupler and not the shaft it will slide on easily without beating it on. Anti-seize compound or at least grease would be a good idea here.

[nofacey]

Doesn’t take a haul out to change the coupling, if you have enough interior shaft length to pull it clear of the coupling….which ou appear to have….

I too would switch to a split coupling - no machining required

[WE9V]

Originally Posted by dcondit

I managed to make a temporary key by using the house batteries to weld some fork tines together.

That's very MacGyver. Props to you (no pun intended).

[sinnerman]

The dimples locations on the shaft are all "chewed up" which indicates that the coupling has been moving around on the shaft for a while.

A new shaft and coupling are in order.

"Proper" method would be for the machine shop to install the coupling on the shaft in a lathe (or similar) and make "true" the flange surface so it is exactly perpendicular to the shaft axis (axial runout).

They then "dimple" the shaft for the set screws.

Heat the coupling to install

cheers

[WE9V]

Originally Posted by LifesBetterWhenYoureBeating

A few days ago my prop shaft slipped off of the transmission coupling while I was motor sailing.

Wow, must be the season for that. I lost my prop shaft too, just one week ago today. I had taken my new-to-me boat out for my first sail, a solo jaunt around Pensacola Bay. I had heard a loud bang shortly after raising sails. I thought I hit a crab pot buoy, or large stick, or it was my folding prop finally folding. I saw nothing behind me as I continued to sail for about 2 hours. At one point, I went below and wondered why there were some puddles of water on the sole. I thought maybe it was just a wet boat.

It wasn't until I was about to come back in, fired up the engine and went head to wind to take in sails. I found I had no propulsion. I went below to check shift linkage and instead I found water pouring into the boat where there should be a prop shaft.

There were two possible root causes: 1) The shaft has a nylock nut for retention. No cotter pin or other safety wire. The nut was too long and didn't allow the nylon to engage on the shaft before it was fully tightened. Therefore, it had no locking feature. 2) The key was insanely sloppy fit. It was found in the bilge, but unknown if the key fell out and THEN the nut came undone, or the nut came undone and then the key fell into the bilge as the shaft fell out.

It was not a pleasant maiden sail.

[OS2Dude]

Oh, and you should check your stuffing box. If your shaft slid backwards at only 4 knots, it may not be adjusted correctly. I'd remove the collar and pull the shaft forward to see if there is any damage to the shaft from wear.

[JimsCAL]

Originally Posted by WE9V

Wow, must be the season for that. I lost my prop shaft too, just one week ago today. I had taken my new-to-me boat out for my first sail, a solo jaunt around Pensacola Bay. I had heard a loud bang shortly after raising sails. I thought I hit a crab pot buoy, or large stick, or it was my folding prop finally folding. I saw nothing behind me as I continued to sail for about 2 hours. At one point, I went below and wondered why there were some puddles of water on the sole. I thought maybe it was just a wet boat.

It wasn't until I was about to come back in, fired up the engine and went head to wind to take in sails. I found I had no propulsion. I went below to check shift linkage and instead I found water pouring into the boat where there should be a prop shaft.

There were two possible root causes: 1) The shaft has a nylock nut for retention. No cotter pin or other safety wire. The nut was too long and didn't allow the nylon to engage on the shaft before it was fully tightened. Therefore, it had no locking feature. 2) The key was insanely sloppy fit. It was found in the bilge, but unknown if the key fell out and THEN the nut came undone, or the nut came undone and then the key fell into the bilge as the shaft fell out.

It was not a pleasant maiden sail.

One easy thing to do to avoid this is to install the shaft zinc just forward of the strut. This will limit the movement of the shaft if it should work loose from the coupling. Shaft will stay in the boat and may even not move enough to come out of the coupling.

[CarinaPDX]

The traditional way of fixing the flange to the shaft is to use a "roll" or "spring" pin. (https://www.mcmaster.com/pins/pin-ty...spring-pins-6/) Ideally a hole is drilled through the flange's coupling before assembly (but can be done in place with a hand drill - precise alignment is not critical), then once set up with the set screws a hole is drilled through the prop shaft using the coupling as a guide. Finally a roll pin is tapped into place to prevent movement of the shaft within the coupling. Without a roll pin the tips of the set screws can shear off and allow the shaft to both rotate and slide out of the coupling. IIRC mine were 1/4" pins (i.e. requiring a 1/4" hole). Wiring the set screws to prevent them from working loose is not adequate, as the failure is often at the tip of the set screws and not a function of vibration working the screws loose.

Greg

[JimsCAL]

I don't agree with the above. Most boat couplings and shafts have a key and keyway. That carries the torque (along with the friction between the coupling and shaft), not the tips of the set screws.

[CarinaPDX]

Originally Posted by JimsCAL

I don't agree with the above. Most boat couplings and shafts have a key and keyway. That carries the torque (along with the friction between the coupling and shaft), not the tips of the set screws.

The shaft and coupling for my old engine did not have keyways, so the spring pin was necessary. But in this case where the keyway and key are loose the spring pin will work as an alternative and will not require removing the shaft for machining of a new or wider keyway. YMMV

Greg

Edit: While the key/keyway approach will prevent rotational slipping it will do nothing to prevent the shaft being pulled aft - that is solely dependent on the set screws. And that was the OP's problem: fixing his key/keyway issues won't solve the problem of preventing the shaft being pulled aft. A spring pin will solve both problems.

[skipperpete]

Grand Banks drivelines sometimes use a really simple shaft coupling retainer, not a roll pin but just a ½” steel dowel in a reamed hole right through the coupling and shaft. It’s not a drive fit and is held in place by a little cover plate at each end which are secured by ¼” screws into the coupling.

[OS2Dude]

Originally Posted by Scubaseas

I disagree with some of this. A prop shaft can come out in neutral. I bet it could come out in drive if the waves were steep enough. .

I didn't say it couldn't. I said if the boat is being driven forward by the propeller, then it could not because the shaft would be pushed into the transmission.

Originally Posted by Scubaseas

I did not know that the output flange was not replaceable (it is) and the whole gear box would have to be replaced. Any decent machine shop could true up an output flange. Most gear boxes the output flange is held onto the shaft by a nut and is easily replaced. Change the seal while you're at it.

Well, the folks at Catalina Direct told me the OEM transmission used by Catalina at the time had an integral flange that could NOT be replaced. I chose not to risk it, but your boat, your choice.

Originally Posted by Scubaseas

I would question the need to balance a 1.25" shaft (if even that much) spinning at less than 1500rpm. There is usually a reduction gear (2:1 or 2.45:1 or 2.6:1.

Our 1985 Catalina 30 has a 1" shaft. (Our original shaft was bronze.) I would hazard to say they all do. The issue is mostly keeping the shaft aligned and not flopping around, even a little. Perhaps 'balanced' was the wrong term.

Originally Posted by Scubaseas

If you heat the coupler and not the shaft it will slide on easily without beating it on. Anti-seize compound or at least grease would be a good idea here.

At least on our boat that is easier said than done. I tried to heat our coupler when I was trying to remove the original shaft, and it was very tight quarters and the fiberglass got singed, even with a heat shield in place. Perhaps later models were redesigned to give more room, but ours is a 1985 model I and IIRC Catalina had just started putting in the M-25 diesel, which is a bit longer than the Atomic 4 it replaced. (Perhaps the Universal was an upgrade at the time, our boat seems to have come with several factory upgrades.) And I said I TAPPED the shaft in, not BEAT it. We were on the hard, so it was the best option.

[Paradox111]

Originally Posted by LifesBetterWhenYoureBeating

That looks great. And it seems to me it just clamps to the shaft with no need for a key or set screw?

Correct no shear key. There are (8) M6 socket head cap screws that clamp the collar to the driveshaft. The Sigmadrive is said by manufacturer good to 3 degrees. Thus no need to align to 0.0001, flexible motor mounts can move that much under load?
https://youtu.be/Cefh8O4o5yI

[OS2Dude]

I was interested in finding out about this item. Not what I had in mind when I read 'Split Collar'. I had something in mind like an anode ball that goes around the shaft.

It is a CV joint with built in thrust bearing. The coupler's inner ring is split and gets compressed onto the shaft when you install it but is still installed by sliding it onto the shaft from the end. It allows a 3-degree deviation from true, so alignment is not as critical.

Here is a web page I found that describes it: https://ab-marine.com/bruntons-sigmadrive/ No price is available on the above website, but the review said it is about $500.00. I spent about $650 for a new faced shaft and coupler, plus shipping. If money was no object, I would consider this over the faced coupler, only because I had to cut my old OEM shaft to get it out of the boat as it was stuck into the OEM coupler, and I had already cut the stuffing box hose to make room for the puller. (Yes, I tried heat, penetrating oil, a puller, etc. No, none of it worked.)