Flexofold prop FELL OFF!!

[fstbttms]

Originally Posted by hugosalt

Addressing post # 2 ....FOF props falling off a number of saildrive charters...

In 2007 had yard install my FOF on saildrive as I did not want to install myself and risk losing prop...at haul out after long season prop was very close to falling off. I reinstalled myself, after reading instructions, this time using the(what I call) "tab washer" that was still in the box. Believe (memory?) it went between double nuts and then the tab was bent down to lock in nuts. Could explain a lot of lost props, at least from Saildrives.
No problem since reinstall but as I used some red locktite, to be sure, I will be in for an adventure removing prop to change seals this year.
(heating to 300 odd degrees)

Also think??? that tab washer(should)be used to lock in nuts on shaft installs
as well but have no 1st hand knowledge.
Any experience/knowledge or manual will have.

So in fact, your Flex-O-Fold loss was due to an improper installation, not because of some supposed flaw in the prop’s design.

Also, shaft-mounted Flex-O-Fold props do not incorporate the use of a tab washer.

[Wotname]

Originally Posted by fstbttms

Nobody laps the prop.

Factually incorrect - as evidenced in part by other posters

Not the manufacturers when boat is commissioned, not the yards when they replace a prop

Factually incorrect - I have only had two new props fitted by experienced professional yards and both times the prop was lapped (one in the mid 80's and the other in early 00's). If that is my experience, then I'm sure others have had similar experiences.

and of course no diver is lapping a prop.

Fair enough, now I know never to engage a diver to fit a prop that hasn't previously being lapped to the shaft.

And that covers 99.9% of all props installed on any pleasure craft. It simply is not standard procedure. And people aren't losing props because of it.

It maybe a standard practice in your 25 years of experience but it certainly isn't best practice.

Often not following best practice is due to ignorance, other times it is due to arrogance and sometimes it is due to a willingness to accept substandard procedures or being unable to pay for best practice. Oh, I forget, sometimes it is simply due to laziness.

[fstbttms]

Originally Posted by Wotname

It maybe a standard practice in your 25 years of experience but it certainly isn't best practice.

Often not following best practice is due to ignorance, other times it is due to arrogance and sometimes it is due to a willingness to accept substandard procedures. Oh, I forget, sometimes it is simply due to laziness.

“Factually incorrect”? OK, now you’re just parsing my words. Obviously lapping a prop is a thing that is done, on occasion. But as I said (and you are unable to refute), it is not a procedure that is used in the vast majority of prop installations, regardless of whether the installation is performed by a professional or not. And since prop loss is a relatively uncommon occurrence, it is fair to say that lapping is not critical to a proper installation. Further evidenced by the fact that the propeller manufacturers themselves make no mention of it in their installation manuals.

[SwellGuy]

Originally Posted by fstbttms

“Factually incorrect”? OK, now you’re just parsing my words. Obviously lapping a prop is a thing that is done, on occasion. But as I said (and you are unable to refute), it is not a procedure that is used in the vast majority of prop installations, regardless of whether the installation is performed by a professional or not. And since prop loss is a relatively uncommon occurrence, it is fair to say that lapping is not critical to a proper installation. Further evidenced by the fact that the propeller manufacturers themselves make no mention of it in their installation manuals.

The materials that came with my prop definitely explained the lapping process, not sure if those instructions were from the manufacturer or the retailer.

Do you read the manuals underwater, too? Maybe that's the problem.

[fstbttms]

Originally Posted by SwellGuy

The materials that came with my prop definitely explained the lapping process, not sure if those instructions were from the manufacturer or the retailer.



Do you read the manuals underwater, too? Maybe that's the problem.

Maybe you would like to back up your statement with proof? Because I assure you I can give you many examples backing up mine.

[Ostinato]

I’ve had one Gori fall off and a friend two Goris. I now have Brunton varifold and no problems so far. But I think it’s both a design and installation problem. Design in that there no pin holding the prop on and installation in that we are not using the right stuff to secure it without pin even when we follow the manufacturers directions. I for one have abandoned the underwater loctite and are using a water curable polysulfide.

[HeinSdL]

When I bought my boat, it came out of the yard where it had been built 8 years earlier and where it had gone a complete service/refit. Was all very well done except the flexofold, which was attached to an SD40, fell off 18 months later.... a warranty issue luckily.

Putting on this prop is something I looked into very carefully and is now something I will only do myself. The yard didnt even manage to do this in a failsafe way and that is the end of the discussion for me. And there are some differences between the locking nuts depending on what the prop is connected to, the only taper there is on the spacer needs to be clean and you need a hard wood plank purpose made which stops the hub from turning when torqueing up nut and securing bolt. Holding the hub with a blade in my view is not sufficient.

[sailorboy1]

I didn’t lap my prop. I fit it without the key and marked it and made sure it went on as far with the key installed to be sure it fully fit onto the shaft with key (just like in the directions the FOF co es with).

I’ve lapped lots of valves etc. but don’t really see the point of lapping a prop for most part. You aren’t really going to change the fit/shape of the prop/shaft unless you want to develop a Lot of time. 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.

I bet the lapping issue is just a red herring. My theory is that prop just wasn’t properly fit and installed and the key bound up and/or it wasn’t fully engaged. Or the shaft nut just wasn’t tightened/installed properly.

[longjonsilver]

Has anyone else noticed how combative and self important some people are?

[kenbo]

Originally Posted by a64pilot

Well, I lapped mine. Used machinist blue and valve grinding compound.
But then a lot of people don’t use a torque wrench on things that should be torqued too, and wheels don’t seem to be falling off of cars either.

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

[HeinSdL]

I thought this thread was about a flexofold going its own separate way and am confused about the lapping discussion. Nothing to do with a flexofold. Thread drift, interesting, but confuses the issue.

[kenbo]

Just some things to consider about fitting a prop to a shaft.

If the interference fit of a taper isn't important, why go through the machining expense of a taper at all. Why not a straight, keyed shaft.

Two parts, a shaft machined in Michigan and a prop hub machined in Denmark. Two different machinists and two different machines. Are you confident that the respective tapers are "good enough" without at least checking with dye? I have, dozens of times, and never saw one set match up greater than 50-60%.

Have you ever seen what happens to a key when that small bearing surface is the main part transferring the torque from shaft to prop? I have rarely seen folks installing props insure that the key is a tap fit to the shaft and free slide fit to the prop.

True enough, fitting a prop is not rocket science but doing it correctly does involve more steps in the process than normally taken. And at times we hear about losing props. Of course it's a low-order frequency occurrence otherwise we'd never leave the dock.

[fstbttms]

Here's the bottom line, as I see it:

There are many, many hundreds of thousands (if not millions) of pleasure craft around the world that have shaft-mounted propellers. Very few (I would venture to guess much less than 1%) have ever had those props lapped. Whether or not this is a best practice, the number of props that are lost in total is very small and the number of those props that are lost due an improper fit on the taper has got to be infinitesimal. A number so small that statistically speaking, lapping is waste of time and effort.

[sailorboy1]

There’s myth and voodoo, and then is basic engineering machine design. One of those covers shear stress design of shaft keys.

Btw - those that feel the taper is important for the shaft/prop why isn’t the transmission end of the couplings tapered

[kenbo]

Originally Posted by fstbttms

Here's the bottom line, as I see it:

There are many, many hundreds of thousands (if not millions) of pleasure craft around the world that have shaft-mounted propellers. Very few (I would venture to guess much less than 1%) have ever had those props lapped. Whether or not this is a best practice, the number of props that are lost in total is very small and the number of those props that are lost due an improper fit on the taper has got to be infinitesimal. A number so small that statistically speaking, lapping is waste of time and effort.

True enough, unless it's your prop that's lying on the bottom.