Lost Flexofold prop!!

MagicalArmchair

MagicalArmchair

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I waved Triola (that I sold to her new owner at the end of last year) off for her 1,000 mile exciting adventure back to her new home port in Poland earlier this week.

The new owner arrived in Amsterdam this morning, and to my horror, calls me and informs me (in a very charming, calm and pleasant way) that the Flexofold prop, that I fitted five years ago (and wrote an article about fitting in PBO 599), fell off as he came to dock!!! The content of the article, and the process I went through to fit it, is here: Fit a Flexofold propeller - Triola - Albin Ballad #50 - Flexofolds instructions are here: http://www.flexofold.com/upload_dir/docs/2-blade-US-shaft-2_0_2013.pdf

I stayed in very close contact with Flexofold during the whole process as I was writing it up, any uncertainty I contacted them and clarified any points.

They know where the prop is thankfully, so are sending down divers to get it, however, this prop would only have fallen off if I would have ballsed something up when I fitted it. What is incorrect in the above? One point in my article leaps out at me:

My concern at this point was two fold, the prop nut locking grub screw, which I assumed would locate onto a flat face of the prop nut was locating onto part of the circular body of the nut. Additionally, there was a bit of unused thread on the nut. I contacted the long suffering (but still very helpful) Flexofold and they advised this was perfectly normal and the grub screw was supposed to locate onto the body of the nut, not one of the faces.
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Going over my emails with Flexofold, I find some other baffling exchanges:

Me (a bitter irony reading it back):
Hello, The hub arrived today, many thanks. I note the prop nut locking grub screw has no thread lock on it – is it worth putting any on? I wouldn’t want my new prop falling off J Thanks
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Flexofold:
No, you don´t need Loctite on the nut. If you just follow the mounting instruction, you can be sure that the propeller will be safe on the shaft. Best regards,
Click to expand...

Questions:
  • Where did I balls the above up? Following the manufacturer's instructions is clearly not good enough. Note to self, trust yourself more, apply more threadlock (although, note in the documentation from Flexofold, it says "There is an underwater proof thread locker pre-applied on all screws in the installation)".
  • When the prop came off, do we think it would have sheered the key and just unwound itself? viz: The diver will be looking for one prop, not many parts of prop?
  • What will the owner need to get the prop back on, presuming the diver finds it? A new key for the shaft?
  • How does the new owner prevent this happening again when refitting?
In the past five years I have done lots of miles under motor, strange it should fail now after five years!
 
Can't answer your question but I can only observe that if the difference between falling off and not falling off was some Loctite there would appear to be a design fault. Castellated nut with a split pin maybe?
 
We were sailing in company with another boat many years ago and we berthed first. As the other boat was reversing alongside (Med mooring) I shouted something like "Give her more reverse welly", only to receive the shouted response "This is full reverse welly". The prop had fallen off when he engaged reverse. :(

Sorry I can help but my Flexofolds are fitted to saildrives and there is a tab washer system which, if I recall correctly, would be impossible to undo unless you bend the tabs back.

Richard
 
I had Flex-o-folds on my boat for16 years, no probs. During this period, they were removed and refitted a few times. The locking grub-screw obviously needs to bite firmly into the retaining nut. Is it feasible that the thread in the prop hub isn't threaded all the way down to its full depth? This would cause the grub-screw to tighten without locking the nut. Not easy to inspect for this on assembly.
 
Losing props does not seem to be that uncommon. If yours stayed on for five years then you must have done it right. Probably the locking screw has slowly worked loose. I suspect the new owner might have made a hasty change from forward to reverse as that seems to be the cause of some propeller losses. I was in Sailors Paridise some years back when a charter yacht came in, turned to come stern first into a berth, then just stopped. The sudden change of direction had spun the prop off. The restaurant rib went out and pushed the boat in. The charter company brought out a spare propeller and nut, and a diver to fit them, but in the event the diver recovered the prop and re-fitted the original.
 
Norman_E said:
If yours stayed on for five years then you must have done it right. Probably the locking screw has slowly worked loose. . .

I suspect the new owner might have made a hasty change from forward to reverse as that seems to be the cause of some propeller losses.
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:eek:
I'm not buying that for a minute.

I would expect a properly fitted prop to stay on forever, unless deliberately removed, except in the rarest of circumstances.

The idea that the prop staying on depends on not changing from forward to reverse too quickly seems laughable to me.

If a prop falls off because of a brisk change of drive direction, or because it's been on for more than a year or two, then it must be insecurely fitted. Insecure fitting must be the result of either (a) incorrect fitting or (b) inadequate design of the securing mechanism.

(P.S. The only trouble I've had with prop attachment is getting the blighters off once they've been on a while.)
 
I had something similar with a Brunton Autoprop in a harbour in an island in Sweden. An anxious hour while a diver looked for it. It was retrieved and we were towed to the mainland where we were lifted and the prop refitted. Only 24 hrs of our holiday wasted - a miraculous result.

it transpired that the grub screw has a fault on its thread and tightened up when it was actually not in contact with the nut. It had been like that for at least two years and could have fallen of in much more embarrassing situations.
 
LittleSister said:
:eek:
I'm not buying that for a minute.

I would expect a properly fitted prop to stay on forever, unless deliberately removed, except in the rarest of circumstances.

The idea that the prop staying on depends on not changing from forward to reverse too quickly seems laughable to me.

If a prop falls off because of a brisk change of drive direction, or because it's been on for more than a year or two, then it must be insecurely fitted. Insecure fitting must be the result of either (a) incorrect fitting or (b) inadequate design of the securing mechanism.

(P.S. The only trouble I've had with prop attachment is getting the blighters off once they've been on a while.)
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That is exactly what happened. After the boat arrived I went for a swim and checked underwater for the charterers and saw the bare shaft. Quite obviously there was an underlying issue like a failure to tighten the nut sufficiently or a broken or missing split pin, but the boat in question had a shaft taper and no keyway so the prop was only retained by the nut and a split pin. When examined the split pin was missing. That type of prop fitting is in my opinion a poor idea as the lack of a key makes it possible for a sharp reversal to slacken the nut and even spin it right off. The boat I saw it happen to was a Beneteau of around 40 feet. My own boat has a substantial key as well as the taper and used a tab washer to prevent the nut coming undone with the old fixed prop. When I removed it it came off without too much difficulty using a puller.
 
I've lost blades from folding props through electrolysis eating the grub screw's surrounding bronze thread and loosening them. Obviously we found the screws (and hinge pin and blade) missing, but it was when we went to fit new that we noticed the looseness.
 
Norman_E said:
That is exactly what happened.
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I'm not for a moment suggesting it didn't happen. I'm suggesting that it happening is not normal, and is the result of either bad fitting or bad design. I think we may be agreed on that.

I don't agree that a tapered shaft without a key will allow the prop to spin on the shaft and unscrew the nut. If the prop can turn on the shaft, the taper of the shaft and that of the prop are not matched. And even if it turns, if prop can then fall off, the locking pin, tab, grubscrew or whatever is missing, or improperly designed or fitted.
 
Sandy said:
That would never happen check them weekly. Not something I do with a prop. Not seen mine in 11 months anode replacement next month.

How often do we all check props?
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Well strangely enough my prop is checked every six months, because I take it off each year on lay up. It gets taken home, cleaned up, polished and greased. I have threatened to plonk it on the coffee table, but so far, have been actively discouraged from doing so. ?
 
NormanS said:
Well strangely enough my prop is checked every six months, because I take it off each year on lay up. It gets taken home, cleaned up, polished and greased. I have threatened to plonk it on the coffee table, but so far, have been actively discouraged from doing so. ?
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Now that is sound advice. I recall many a story of owners arriving at the boatyard at the beginning of the season only to find their expensive folding prop was missing. Grrrr
 
Just looking at the installation instructions...

Why is the prop nut not entirely hexagonal, with a washer if necessary, so that the grub screw can sit against a flat?

Mine is, but I don't know the prop make, 1985 vintage, just says Sweden on it.

If the screw has to engage on a cylindrical surface, shouldn't there be an instruction to create an indent for it?

I have grub screw indents in the pivot pins on mine.
 
What has happened is when the new owner has come into port, he has put her hard hard astern, for some reason the taper was not causing enough grip (I'm thinking the taper must have been contaminated with oil perhaps from the lapping process? That's a failure (my failure) of fitting) and its sheered the key. The locking grub screw has clearly failed also, that's a failure of design.

The divers came up empty handed - the mud clearly swallowed the prop taking any evidence sadly with it.

The owner has located a 25mm prop, and needs to get home. The shaft is 1". I believe a metric shaft has a metric taper of 1:10, and this Imperial shaft will have an imperial taper of 1:12 - making this a tough fit. He needs something to get him the 600 miles or so home else he will lose his crew. He could get hold of a nut to fit the prop with, use thickened epoxy to even up the tapers, and to fill the keyway? Or is that a bodge too far? I doubt he'd ever get the bleeding prop off again without cutting it off...
 
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