Flexofold prop FELL OFF!!

[Ndavies]

I know this is an older thread.....but I just lost a Flexofold off my 2019 Lagoon 40. I have no clues as to why. I purchased the boat new and sailed her back from France and she is used regularly. I have now sailed it more than 10,000 miles and have over 500 hours on the engines. I suspect this was an installation issue, but the props have not been taken off the boat since commissioning. Its hard to think this was an installation issue after so many miles.........but I don't have another explanation.

The new prop is on the way, my wallet is significantly lighter. I plan on hauling the boat to install the new prop and thoroughly check the remaining one. I ordered additional installation hardware and my re-install the remaining prop to be sure its on correctly.

[Pillroller]

My commiserations especially after so long and many miles.
Mine came off because he grub screw locking the hub to the Prop-shaft was not tightened up. It came off when I changed from forward to astern gear. Naturally?
Be interested to know what is left on your shaft if anything.
friend8yl@btinternet.com

[Ndavies]

Thanks Robin!
Ergh.....only money! Amazingly the only thing left on the shaft was a spacer that goes on the shaft ahead of the hub. When I went into the water to check it out (after sailing 50 miles) the spacer was still there and slipped right off in my hand. And a darn good thing too - the new prop just arrived. The spacer is shown on the installation guide but says "spacer - not supplied". Man I would be pissed off if I hauled the boat to install the prop and found I was missing a spacer!! Planning to do a short haul Monday morning to install the new one and thoroughly check the other. I know it can be done in the water........but want to be sure this is done right.

[HeinSdL]

Originally Posted by Ndavies

Thanks Robin!
Ergh.....only money! Amazingly the only thing left on the shaft was a spacer that goes on the shaft ahead of the hub. When I went into the water to check it out (after sailing 50 miles) the spacer was still there and slipped right off in my hand. And a darn good thing too - the new prop just arrived. The spacer is shown on the installation guide but says "spacer - not supplied". Man I would be pissed off if I hauled the boat to install the prop and found I was missing a spacer!! Planning to do a short haul Monday morning to install the new one and thoroughly check the other. I know it can be done in the water........but want to be sure this is done right.

Identical experience to the one I had after taking delivery of my boat from the yard. Only explanation: wasn't put on properly. But I have learned in the meantime there are different nuts to be used depending on the application. On my SD40 the nut is noticeably thicker than the nut that comes with the prop. I am still no expert on this but I do use a new locking screw every time (with the pre-applied thread lock) and have a convincing way to lock the central hub when torqueing up (a piece of hardwood reinforced with metal strips that fits exactly where a blade later goes and jams against the hull).

But all in all I don't like the locking mechanism of the flexofold. You're relying on the locking screw to not come undone because of the thread lock and for that screw to hold the nut via some flimsy ring which needs to be deformed. If the locking crew does come undone it won't stop the nut anymore because they both rotate the same way, left hand thread for the locking screw would have been good. I miss a grub screw which could have been used from the side to lock that nut, but no.

Upside is that I now manoeuvre assuming the prop just fell off. And I do like the performance of the prop, very much. Would choose it again.

[Pillroller]

The thin nut should go on the shaft first with the thicker not second no washer between. My hub has a grub screw bearing on the shaft so the nuts could come off but the hub is still unable to move and is wedged on the taper.
Happy sailing.
Pillroller.

[HeinSdL]

Originally Posted by Pillroller

The thin nut should go on the shaft first with the thicker not second no washer between. My hub has a grub screw bearing on the shaft so the nuts could come off but the hub is still unable to move and is wedged on the taper.
Happy sailing.
Pillroller.

The assembly on the saildrive is a bit different. Best thing to do is check with flexofold that you have the correct hardware and then follow the instructions. Then all is well, as per my experience since my incident.

[At Peace]

The lapping process is akin to “custom fitting”. Even the slightest ridge on shaft or prop hub bore, can give an incorrect fit? If done with care and precision (very easy process) at first install, it should never needed to be done again. If you have two engines and removing both props at the same time, just make sure the same prop goes back to its original installed engine.

[FlyingScot]

A few weeks ago I noticed one of my bolts had started backing out and was bent. This was quite a surprise. I had ordered extra bolts when I placed my order so it wasn't a big deal, just had to change it. It could have been much worse if I would have lost a prop. I don't have spare FoF prop on hand, but would consider it for longer travels.

[fcftampa]

Originally Posted by kenbo

True but there are a lot of folks driving cars with pulsating brakes because the disc is warped by uneven lug bolt torque.

so, that's what's wrong with my cars brake! I thought PO had bought cheap discs. thanks

[dfelsent]

Originally Posted by fcftampa

so, that's what's wrong with my cars brake! I thought PO had bought cheap discs. thanks

Or overheated from a hard stop. I had that on my 1972 Plymouth valiant (my grandmas car!) after one very hard stop with cheap aftermarket rotors. Glazed the pads right up too. $100 stop. Cheaper than the alternative which would have been a wreck in traffic.

[hughvr]

After 10 years, I lost my Flexofold mid-Atlantic on a 500 nm passage to the Bahamas. I temporarily replaced it with a fixed prop but later had the boatyard that installed it (when my shaft was replaced) put a new one on. I also now have a spare with all parts. Not sure if it was an installation problem, or something else. At least I am experienced at underwater prop replacement now.

[hugosalt]

Welcome to CF,
Sorry for your troubles.
Do not know if your FOF on a shaft requires a tab washer,
I do know improper installs on saildrives have caused losses.
Some (professionals) don't realize tab on washer needs to be bent over nut.
In addition I personally use red loctite when reinstalling, never a problem removing
with proper leverage.

[SailingHarmonie]

Originally Posted by sailorboy1

The taper fit isn’t what transmits the torque, it’s the key. Just because a prop presses onto the shaft and you can’t remove it by hand is meaningless.
.

This is actually NOT correct, or at least should not be correct.

In a properly fit prop, it IS the friction with the shaft that transmits the torque. If the prop is installed correctly. That is why it is important that the key not interfere with the fit of the prop on the shaft. In fact, on some ship propeller installs there is no key at all, only friction.

In a perfect world, with perfect machining, lapping would be unneeded, because the prop and the shaft would both be bored to exactly the same specs. I don’t live in that world.

If the key was the actual torque transmitter, there would be no need for a tapered shaft.

Many, even most, props are not optimally installed. Just because a substandard install is usually “good enough” is not reason to aim below the correct approach. A good fit is important. Just like getting the prop nuts on in the wrong order (like 95% of diy mechanics do) it’s not always an immediate disaster, but… When I am out on passage, it’s me against the ocean. I want every possible advantage.

[David B]

Originally Posted by SailingHarmonie

This is actually NOT correct, or at least should not be correct.

In a properly fit prop, it IS the friction with the shaft that transmits the torque. If the prop is installed correctly. That is why it is important that the key not interfere with the fit of the prop on the shaft. In fact, on some ship propeller installs there is no key at all, only friction.

In a perfect world, with perfect machining, lapping would be unneeded, because the prop and the shaft would both be bored to exactly the same specs. I don’t live in that world.

If the key was the actual torque transmitter, there would be no need for a tapered shaft.

Many, even most, props are not optimally installed. Just because a substandard install is usually “good enough” is not reason to aim below the correct approach. A good fit is important. Just like getting the prop nuts on in the wrong order (like 95% of diy mechanics do) it’s not always an immediate disaster, but… When I am out on passage, it’s me against the ocean. I want every possible advantage.

I go with all that - the taper is the 'key', and the key is the back-up.
Do it right - do it once, and if you don't do it yourself, keep an eye on the person who does!
There are real experts out there - then there are the others .....

[sailorboy1]

guess you guys never took mechanical design

but I don' care and am amazed you dug up such an old thread