Flexofold prop FELL OFF!!

[Wotname]

Originally Posted by fstbttms

Statistics prove otherwise. It is done every day, all over the world with no issues.

I know I shouldn't be doing this but I gotta ask...

What statistics might they be????? or is done every day, all over the world with no issues the statistic?

[fstbttms]

Originally Posted by Wotname

What statistics might they be?

We've already been over this. Millions of props have been installed on shafts with no lapping. The vast majority of props are never lapped. Yet prop loss is relatively rare. A minuscule percentage of shaft-mounted props fall off. And in my experience, this is typically due to poor maintenance, not because the prop wasn't lapped.

[Wotname]

Originally Posted by kenbo

Just so folks who maybe contemplating a Flex-o-fold, there was no evidence that the FOF prop hub had a bad taper. Only that the mating to that particular shaft was inadequate. Could have been the shaft's machining.

While possible, the link does suggest in this case it was the prop and not the shaft.

Quote This shaft was brand new and made by a shop that does military shafting and has the calibrated dies to test the taper. Not all shops have or use these calibrated test dies and they are normally only used to make sure the machines are in tolerance. This taper was tested, with Blue, and was spot on. That leaves the Flex-O-Fold prop taper as the likely culprit here.

However it doesn't matter which is in error, it highlights that considerable errors can exist.

The OP paid a professional diver to fit the prop. The prop fell off - highly highly likely to a poor installation. Thus it is highly highly likely the diver either knowingly or unknowingly did not fit it correctly. The OP is now wiser (post #14). Don't know if the diver is though.

[sailah]

Here's how I would do it. I've had work done by Keith and he's a true pro when it comes to marine shafting. This is him showing how to lap and fit a prop. When I removed my Max Prop to change bearing, I did the same test with Dykem and had great contact so I didn't do any lapping.

He specifically states that the taper interference fit is what holds the prop. Key, nut, cotter are just safety measures.

https://www.youtube.com/watch?v=2ozh4JjoWm4

https://www.youtube.com/watch?v=o5lW9ACWGrY

[sailah]

And another good video on fit and facing of a coupling.

https://www.youtube.com/watch?v=RyKU...23D965&index=3

[HeinSdL]

Originally Posted by Wotname

Maybe not as much drift as you think .

We know the prop fell off after 2 months and a thousand miles of motoring.
We know it was fitted underwater.
We are advised by one professional hull driver that lapping is not done underwater.
The link in post #80 tells of a new Flex-O-Fold prop that had a very poor taper.
The consensus is the prop fell off due to an improper installation, not due to a design defect in the prop.
What remains unknown is where the installation was flawed. While there are several possibilities where the error occurred, one of them must be the failure to ensure sufficient contact area in the taper - as suggested by Kenbo back in post #11.

Another question which still remains unclear to me about fitting a prop underwater and checking the taper fit / lapping - is it simply not done because it is very difficult to do or is it not done because it can't be done????

I learn as I go... now I know the flexofold is attached via a taper on a shaft and a spline on a saildrive (as I suppose is the case for all props). I also lost my flexofold having taken delivery of my boat out of the yard so was following the discussion with interest until the taper discussion came along... But now I know something new which won't be immediately applicable to my situation.

[JPA Cate]

Another question which still remains unclear to me about fitting a prop underwater and checking the taper fit / lapping - is it simply not done because it is very difficult to do or is it not done because it can't be done????

That's an interesting question, Wotname.

In this case, it was not like what the divers usually deal with, a prop and shaft already mated. [The prop was new.] There was a problem, fortunately not a disastrous one.

Usually, Fstbttms methods have worked well for him, and his customers, if we accept what he says as written. Maybe the picture of him with the wrench with the long handle tells a meaningful story?

In retrospect, it seems the OP would have had better "luck" if the shop who did the shaft would have mated the prop, and removed same for the installation into the boat....but perhaps it did not arrive in a timely fashion.

Ann

[Oceansailor]

I think there is to much focus on the lapping procedure. I do agree with Fstbttms that lapping is not the standard in the industry. Normally taper is good enough. A professional will detect that when installing the propeller. Propeller riding the key, or nut bottoming out on the shaft is much more likely reasons for loosing the prop. All this is so easy to check on the hard. In murky water it is another story. Much easier to miss something.

[Wotname]

Originally Posted by Oceansailor

I think there is to much focus on the lapping procedure. I do agree with Fstbttms that lapping is not the standard in the industry. Normally taper is good enough. A professional will detect that when installing the propeller. Propeller riding the key, or nut bottoming out on the shaft is much more likely reasons for loosing the prop. All this is so easy to check on the hard. In murky water it is another story. Much easier to miss something.

Just to be clear, the OP had a new prop fitted than existing shaft.
Perhaps you could explain to me the process the professional would use to detect if the taper is good enough?

[Oceansailor]

Originally Posted by Wotname

Just to be clear, the OP had a new prop fitted than existing shaft.

Perhaps you could explain to me the process the professional would use to detect if the taper is good enough?

There is a difference between detection and lapping. Detection can be done in many different ways. On the hard easy. Under water is much more difficult.

[kenbo]

Originally Posted by Oceansailor

There is a difference between detection and lapping. Detection can be done in many different ways. On the hard easy. Under water is much more difficult.

Isn't that exactly the reason why a new prop shouldn't be fitted underwater?

[Oceansailor]

Originally Posted by kenbo

Isn't that exactly the reason why a new prop shouldn't be fitted underwater?

I agree. It is a VERY high probability that the diver made a a mistake. This type of propellers do not fall of if installed correctly.

[Wotname]

Originally Posted by Oceansailor

There is a difference between detection and lapping. Detection can be done in many different ways. On the hard easy. Under water is much more difficult.

I agree with the parts emphasised but I am only aware of one method of detection (outside of a specialist lab) that universally ensures the taper fits correctly.

Perhaps you could comment of the many different ways that can be used on the hard?

[skipperpete]

It's actually possible to detect a propeller that is loose on the taper from inside the boat by putting a wrench on one of the (tight) coupling bolts and quickly rotating the shaft through maybe 10° ahead then astern. This needs to be done vigorously and if the propeller is loose a definite "clunk" can be heard and felt. An additional advantage is that a loose shaft coupling shows up with this test too but it really only works with fixed blade propellers, the folders and featherers have their own clunks.

[CarlF]

While an interesting back and forth discussion, lapping has nothing to do with the OP losing his prop.

The Flexofold installation instructions do NOT have you check for contact area or do any lapping. If the manufacturer isn't concerned, I think we can assume it was not the reason the prop fell off.

As an owner of Flexofold shaft mounted three-blade prop on two boats over 12 years, I think it's likely that the OP's diver did not correctly install a set screw that keeps the shaft nut from turning. With this set screw in place, even a mismatched taper would not result in the prop coming off as the prop nut can't turn (assuming a properly fit key was also in place).

This is a small screw that goes in a small hole on the side of the hub. Easy to miss. Especially underwater. Most props don't have such a screw so unless the "professional diver" had installed a bunch of FlexoFold's before, he would not expect this screw.

It's a great design - you just have to follow the instructions. If I was to get another boat, it would also have a FlexoFold.

Here's Step 2 in the instruction taken from the CURRENT FlexoFold website: