Prop Fell Off! Help!

[SeaKing]

Hello Strygaldwir, I have kept a cat in Shady side for 7 or 8 years at least. We are at Wood's Wharf otherwise known as Billy Groom's. Where is your boat and what is the name. We are Seapaws II, our previous Seapaws was a PDQ.

We are hauled at Georgetown Yacht Basin up the Sassafras River. The only place that can haul us. There is a place in Pasadena also that may haul you. I would have to look up the name. I had previously used Herrington Harbor North in Deale, our PDQ had an 18'beam. You should call them to check, there is a West Marine right at the front of the marina yard.

I'll let you know when we have the boat back in Shady side.

[Steve Rust]

Sean
Mine is a Volvo saildrive so there seems to be a design difference in how the prop is attached. Not that it helps any but I find this to be an inexcusable design flaw by Yanmar especially as it seems to be a not uncommon experience. I know Volvo gets bad mouthed and maybe for good reason but my drive is 26 years old and my experience and that of the PO have been trouble free except for routine replacement of seals.

[ssullivan]

Originally Posted by Steve Rust

Sean
Not that it helps any but I find this to be an inexcusable design flaw by Yanmar especially as it seems to be a not uncommon experience.

I'd say so. Definitely inexcusable. The cone is an option, which my saildrives have. I am going back to the standard locking nut, which supposedly actually will lock on there, rather than just hoping an allen bolt will stay put through torque alone.

[Fishspearit]

Now you know what those cages were on there for..... to catch the prop when it fell off!

[David_Old_Jersey]

Originally Posted by Fishspearit

Now you know what those cages were on there for..... to catch the prop when it fell off!

Ouch

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[Alan Wheeler]

To be safe, I plan to do as Wheels says and put some locking locktite on there.

Just to ensure you have it clear, NOT on the Shaft. Keep the shaft dry and clean. Use locktite on the set screw thread ONLY.
The prop will be hard to get off. It is supposed to be. that is why the tapered shaft fitting is so good. It has an enormous load transfer area and does not rely solely on a keyway.

Not that it helps any but I find this to be an inexcusable design flaw by Yanmar especially as it seems to be a not uncommon experience.

It is NOT a design flaw. The flaw is in people applying the design in the wrong way. Like applying a coating to the surface. Easy to do when you don't fully understand and just thinking your efforts are supposedly helping the situation. Tapered systems have been successfully used long before Yanmar and by many more other than Yanmar. It is a good reliable system as long as the rules of application are followed.
When it does come time for removal, a little heat and a thump in the right place and it will pop off.

[ssullivan]

Wheels, you obviously know what you're talking about here.

What do you think of the method of only having a single allen bolt (part number 68 in the linked diagram) holding the prop and cone in place?

I am thinking of changing to the standard hardware, which was only a prop nut with some kind of torque nut (parts 43 and 50 in diagram) that will keep it in place. The cone has *no* provision for keeping the allen bolt in place. Nothing but the torque on the allen bolt holds it in place.

(see diagram - I have the "optional" hardware rather than a standard prop nut):

http://www.cruisersforum.com/forums/...7&d=1210030280

In that diagram, I have part number 68 and 64 instead of part number 43 and 50. Which do you think would be best of the two choices?

Originally Posted by Alan Wheeler

Just to ensure you have it clear, NOT on the Shaft. Keep the shaft dry and clean. Use locktite on the set screw thread ONLY.
The prop will be hard to get off. It is supposed to be. that is why the tapered shaft fitting is so good. It has an enormous load transfer area and does not rely solely on a keyway.

It is NOT a design flaw. The flaw is in people applying the design in the wrong way. Like applying a coating to the surface. Easy to do when you don't fully understand and just thinking your efforts are supposedly helping the situation. Tapered systems have been successfully used long before Yanmar and by many more other than Yanmar. It is a good reliable system as long as the rules of application are followed.
When it does come time for removal, a little heat and a thump in the right place and it will pop off.

[Morgan Paul]

Now you know what those cages were on there for..... to catch the prop when it fell off!

Hey that makes sense !

[ssullivan]

Also, given that the setup without the cones has basically nothing but friction to hold it in place, is there really any difference?

I am now thinking I might go with what I currently have (had?) because I'm recalling something:

The cone had a bit of the inside of it broken off. My theory is that maybe this imbalance caused the cone to wobble (especially when it was being pulled through the water spinning at 6-8 knots yesterday sailing) and that wobble moved it on its axis so that it backed off the threads.

Any merit to that theory?

[Therapy]

Not that it helps any but I find this to be an inexcusable design flaw by Yanmar especially as it seems to be a not uncommon experience.

Originally Posted by Alan Wheeler

It is NOT a design flaw. The flaw is in people applying the design in the wrong way. Like applying a coating to the surface. Easy to do when you don't fully understand and just thinking your efforts are supposedly helping the situation. Tapered systems have been successfully used long before Yanmar and by many more other than Yanmar. It is a good reliable system as long as the rules of application are followed.
When it does come time for removal, a little heat and a thump in the right place and it will pop off.

Flaw or not I think splined shafts and cotter pinned castle nuts have proven better. Anything that can rotate in such a manner as to unscrew the single nut holding should be held together very well, not pretty well.

I am amazed that the design is used still, unless there is no reverse.

[Alan Wheeler]

The tapered shaft method is found on almost all through hull shaft systems. It is common and found the world over.
I say once again. There is no design flaw, only incorrect application.

[Steve Pope]

Sully, The nut option is obviously threaded so methinks the cone should be threaded too, Is the cone threaded? Has it been threaded but now is stripped of thread? on the diagram of the cone there is a dimple (hole?) showing is that for a pin to tighten the cone if threaded and if threaded how tight can you get the cone? If that is the case then the allen headed bolt is your locking device and a touch of Loktite to the thread would stop it undoing.

[Alan Wheeler]

The cone had a bit of the inside of it broken off. My theory is that maybe this imbalance caused the cone to wobble

No absolutely not.
The prop nut should be tightened to the correct torque. This pulls the prop onto the shaft and if it has been done correctly, the nut should be able to be removed and you should not be able to pull the prop off with out a smack with a hammer. The safety system is the Nut and the set screw. There simply is no way either can come out with a wobble of the nose cone. The nut is there for the one reason of ensuring the prop does not come lose due to improper gear changing, like that clunk when put into gear when the engine still has too many revs on it. That is not the best for things. The set screw is the "Lock" for the prop nut. The two can or should not be able to simply come loose. Even with a vibration of the nose cone.
The issues will be....The anti-seize applied to the shaft has stopped the prop pulling up properly onto the shaft. The prop has worked it's way on over a long period of time while the engine is in gear and the prop pushing hard onto the shaft. Therefore the nut will now be loose and the set screw may possibly also become loose. Not sure how, but obviously it has.
Sean, the drawing only shows the splined shaft, but I assume the tapered the shaft also has a keyway, is that correct??

[David M]

I found it!

Ya want it back?

[Alan Wheeler]

Yes Steve. There are two options. A splined shaft and a tapered shaft. The splined shaft uses a nut and set screw and the tapered shaft system uses the nose cone as the prop nut. The cone should have an 16x20 thread insert. It also has a set screw to lock it in place.