Flexofold prop FELL OFF!!

[Wotname]

Originally Posted by flyingnut40

I skipped the last hundred posts TTTR.....
but my take on the thread is this.
Morse tapers are machined to an industry standard and IF the prop is new and IF the shaft is new and properly made the two parts WILL mate with 80 -90% contact and the nut will seat the tapers together with enough contact area that the nut "could" be removed with no consequence.... but you wouldn't. Locktite or set screws are EXTRA insurance that like any bandaid won't work forever. If the prop/ shaft has ANY DEFECT it WILL affect the mating performance of these two parts and machining or lapping or both will be required to get that 80-90% contact. When I am faced with this challenge you can bet that I will be getting some bluing agent or in a pinch a light spray of paint (something!!) And cheching the mating of these surfaces! Lapping is great insurance. Lots of parts are held by Morse Tapers...... like flywheels etc. and virtually Always require a puller to get them to release the "lock" that a proper taper gives.
If there is even the slightest score on either surface then the working of the parts will flatten the defect and you have loose parts. Now you are at the mercy of the bandaid!
Keyways are to locate part orientation and earlier posts are valid. Ket needs to fit tight in shaft and have enough clearance to not impede the 80-90% contact area of the taper. The keyway might drive a go kart axle for a while..... it WILL NOT drive your boat!
Good luck with this! The engineering is sound!
Dennis

You make a good point about the necessity of the matching the taper however just to be clear, prop tapers aren't often Morse tapers (although some are), in fact there are a variety of prop tapers in use.
This link explains some of them
Taper Charts and How to measure propeller taper bores

[Pillroller]

Hi.
I had this happen in my mooring in a basin.. My friends had launched my yacht whilst I was in Hospital. Luckily a neighbour was on his boat and offered to look for the prop with his scuba kit at the weekend. £/4 hours later no luck, " just one more try under the pontoon", 5 mins later popped up with prop.
I had come of intact but the locking grub screw on the boss was not done up!!!
So I guess this could be a cause in other cases? I wind it in tight now and so far so good.
P.S.
As we were cleaning up the diver, I hosed off the prop. Turned and pulled the hose, but it snagged on a cleat. This pulled the hose taught like a bow string firing the prop back into the water. We saw where it went, more or less, but unable to find before his air ran out. Next weekend I hung chains from pontoon and my neighbour's prow to give him a reference position,as the water is very silty.
He went into the water I saw his bubbles go round his bow and seconds later a hand holding the prop was thrust into the air.
Besides getting my prop back, I also got a bottle of whisky. from PBO magazine, as letter of the month.

[flyingnut40]

If in fact they are not using a standard Morse taper then I have even more concerns about the mechanical fit (misfit?) that is possible. Checking becomes mandatory.... more for the custom shaft than the batch produced propeller hub.
But they MUST match 80-90% to stay together with the reliability that we demand.
As for the splines on a sail drive? I wouldn't take one if it was given to me..... not offshore at least. You have a slip fit and are completely at the mercy of the locking scheme provided, be it crown nut and cotter pin, locknut or folding tabs etc.after that fails your prop is gone!
D

[flyingnut40]

Did some reading and there is a lot of tapers in use. Morse is around 19:1 and props can be 16:1 or 10:1 so it must be checked. Thanks for the link! Get the taper wrong and you might only have 5% contact!
With the cost of props I'm not guessing!!

[David B]

Originally Posted by flyingnut40

If in fact they are not using a standard Morse taper then I have even more concerns about the mechanical fit (misfit?) that is possible. Checking becomes mandatory.... more for the custom shaft than the batch produced propeller hub.
But they MUST match 80-90% to stay together with the reliability that we demand.
As for the splines on a sail drive? I wouldn't take one if it was given to me..... not offshore at least. You have a slip fit and are completely at the mercy of the locking scheme provided, be it crown nut and cotter pin, locknut or folding tabs etc.after that fails your prop is gone!
D

We have the splined Flexofold for our saildrive. Very secure. The precision fit on that shaft is impressive (especially considering two different companies made the shaft and prop), so there is no play there. Then the locking and retention system - done properly, is more secure than a grub screw. A grub screw - especially one fixed underwater, can come loose. A tab washer - unless there are underwater monkeys causing trouble, remains bent.

Here is a vid I did showing the reassembly of a Flexofold on a splined shaft. I need to add more 'Boat Tech' vids, but this one will do for now:

https://youtu.be/fConQRkPfMM

[David B]

Originally Posted by Per Weiskvist

Hello in this forum

One of our clients, emailed us about this thread, so I think it will be good if I place a comment and a few advices, to this issue.

A Flexofold propeller normally dont just fall off. But there are a few things you need to be very aware of :

First of all, if you suddenly feel vibration from the shaft/saildrive, that was not there before, stop immediately and get a propeller check....

To prevent this :

1. The hub taper must fit perfectly, so please make sure to order the right standard taper.
2. The hub is not allowed to ride the key when mounted (you might feel this by some vibrations from the propeller/shaft).
3. By shaft installation, it is VERY important to remember, to fit the little locking screw on the side of the hub, and make sure it locks the nut on one of the flat sides of the socket.
4. By Saildrive installation, it is VERY important, that you fit the locking screw and the tab washer on the nut. and it is VERY important to make sure the tab washer is locking both backwards the locking screw, and forwards the nut, so needs to be bended both ways.

I hope this prevents any other member of this forum, to unfortunately loose a Flexofold performance propeller.

Per Weiskvist
Flexofold Aps
Denmark

Thank you Per.
I was expecting sooner or later someone from Flexofold would drop in. Unfair to suggest as some have, that the prop falling off is due to a design fault - especially when the installation was done underwater and no one other than the diver saw what was done or not done.

Out of interest I understand the splined version uses a tab washer, and the shaft version uses a grub screw for locking the retaining nut. Neither versions can rotate the hub on shaft (splines or key prevent this), so why is the grub screw used on the shaft version?

[Hotspur0621]

I have had a Flex o Fold on my Sabre 362 for 4 years. 1,825 nm last winter in the Bahamas; never a problem. Love it. I would not install unless on the hard.

[Wotname]

Originally Posted by David B

.......
Here is a vid I did showing the reassembly of a Flexofold on a splined shaft. I need to add more 'Boat Tech' vids, but this one will do for now:

https://youtu.be/fConQRkPfMM

Nice vid, thanks for posting it

[Seman]

I would suggest the spline key was not installed. That would allow the nut with whole assembly to unscrew and the complete prop fall off.

[rom]

Originally Posted by David B

Here is a vid I did showing the reassembly of a Flexofold on a splined shaft. I need to add more 'Boat Tech' vids, but this one will do for now:
https://youtu.be/fConQRkPfMM

you are coutning blades number 1 2 & 3 like they were different , can you explain ??
Also FoF does not recommend grease but does recommend/prompt for loctite on every screw.

[Per Weiskvist]

Originally Posted by David B

Thank you Per.
I was expecting sooner or later someone from Flexofold would drop in. Unfair to suggest as some have, that the prop falling off is due to a design fault - especially when the installation was done underwater and no one other than the diver saw what was done or not done.

Out of interest I understand the splined version uses a tab washer, and the shaft version uses a grub screw for locking the retaining nut. Neither versions can rotate the hub on shaft (splines or key prevent this), so why is the grub screw used on the shaft version?

David,
The propeller runs very fast, and besides the normal use in forwards switching to reverse and vice versa, which causes some heavy maneuvers on the propeller, even the smallest unalignment in the shaft, shaft bearing, engine mountings etc., will cause a little vibration. Vibration can potentially loosen the nut/hub over time, so we designed a double securing system on all our propellers, just in case :-). Not many things are worse than finding out the propeller is missing, when you are finally inside the Harbor in windy conditions and want to dock safely.....
All saildrives are designed with a thread for locking screw in the "shaft end", shafts for shaft installations are not.

[sailah]

Standard marine shafting is 3/4" per foot taper. Morse tapers vary but are closer to 5/8" per foot

https://littlemachineshop.com/reference/tapers.php

Western Branch Metals is the largest shaft manufacturer in the world, and maker of Aqualoy shafting. They specifically call out checking the fit of the hub with Prussian Blue and correcting with lapping if not satisfactory.

https://studylib.net/doc/8157336/sha...-branch-metals

Nice 4 part video on some larger shafting, including heat straightening of brand new Aquamet shafting.

Other videos show the effect of improper hub fitting, being key bound, and die checking of shaft that shows the key being slammed from poor taper fit.

Hard to argue the merits of lapping for proper fit. But without checking, how can you be sure you DO have a proper fit?

https://youtu.be/8ZJFP9vEFJY?t=747

[jragman8]

I had the same situation with Volvo's folding props. I know they are not the same, but this is for anyone reading with the Volvo's should be aware of. There is a washer with a small tab. If that washer is not installed right, the whole hub can spin off after a while. Not necessarily right away. I happened to lose the whole assembly in a small harbor in Nova Scotia and had a diver go back and find it. Due to the high tides on the west shore of Nova Scotia, I was able to put it back on the correct way without hauling her out. Ironically, after I sold the Prout 45, the new owner had the same problem when the yard doing some repairs after the sale installed that same washer the wrong way. I did love that folding three blade prop. Wish I had them now on the 50 instead on fixed 2 blades.

[David B]

Originally Posted by Per Weiskvist

David,
The propeller runs very fast, and besides the normal use in forwards switching to reverse and vice versa, which causes some heavy maneuvers on the propeller, even the smallest unalignment in the shaft, shaft bearing, engine mountings etc., will cause a little vibration. Vibration can potentially loosen the nut/hub over time, so we designed a double securing system on all our propellers, just in case :-). Not many things are worse than finding out the propeller is missing, when you are finally inside the Harbor in windy conditions and want to dock safely.....
All saildrives are designed with a thread for locking screw in the "shaft end", shafts for shaft installations are not.

OK, so what we are saying is that if the shafts had the thread on the end for the locking screw and tab-washer, you would use the tab washer there too as with saildrives.

Thanks Per, for the explanation as to why.

[David B]

Originally Posted by rom

you are coutning blades number 1 2 & 3 like they were different , can you explain ??
Also FoF does not recommend grease but does recommend/prompt for loctite on every screw.

Yes, as per the video, every single component is retained by another, which is retained by another until we get to the end plate that supports the anode. Those three, then the single screws need locktite or similar (in fact the kit from Flexofold comes with a pre-coated screw to retain the anode if fitting underwater).

As to the blades,, I considered it is always good practice to replace from whence they came so that lapped surfaces remain that way (as in lapping from normal use). With some props, there is a difference too as to how the gearing meshes, so again, I always replace as per the original assembly out of good practice.