Flexofold prop FELL OFF!!

[waterman46]

Originally Posted by kenbo

Not disparaging the diver who installed the prop but if it was a new prop and it wasn't properly mated to the shaft taper it wasn't installed properly. Many believe it's the prop nuts that hold the prop onto the shaft but it's actually the interference fit of the taper that holds it in place. If you don't think that's the case try taking a prop off without a puller.

Yes, so if the entire prop falls off it is really strange unless there is a complete fracture of the hub. But apparently this didn't happen to the catamaran owner who was able to find his Flexofold prop, undamaged, on the harbor bottom.

I don't know about other boats, but mine have had the castellated prop nut secured with cotter pin. I don't see why one would rely on LockTite alone, and I certainly would not.

[Wotname]

Originally Posted by sailorboy1

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

Err... they are. Perhaps more correctly - some are and some aren't.

In my case with four boats, two had tapers on both ends of the shaft and I don't know about the other two; I never had reason to remove the transmission end coupling.

[skipperpete]

I'm on the fence about lapping tapers because I've never seen it done but I guess it would be a reasonable way to match the tapers.it might even lock the prop on tighter because of the concentric lapping scores. Our usual shipyard procedure is to polish the shaft taper and apply a very thin smear of bearing blue to it.... then offer up the propeller to the taper and see where the blue is deposited. Then scrape off the blue areas and a tiny amount of the underlying bronze propeller bore with a bearing scraper tool until no blue areas remain. Reblue the shaft, refit the propeller and repeat the process until a minumum 80% blue pattern is achieved. At no time is the shaft scraped or sanded. Finally, fit the key and check the blue pattern with it in place and you're done. [emoji28]

[Wotname]

Originally Posted by sailorboy1

.....
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.

Actually it is quick process. The bronze prop hub is quite soft and wears rapidly. Obviously the time is dependant on how well the tapers fit initially but 15 minutes is a reasonable average.

[Wotname]

Here is a marinehowto article and pictures on prop fitting and lapping.
It specifically mentions a new Flex-O-Fold hub that only had a 15% to 20% contact area when first fitted. I doubt that could be correctly fitted underwater.

https://marinehowto.com/lap-fitting-a-propeller/

[Wotname]

Originally Posted by Tellie

Fstbttms may be somewhat peremptory, but ignorant he is not by any measure. I'd listen to him over most.

I agree, he certainly isn't ignorant; ignorance suggests a lack of knowledge of the the subject and we know the correct information has been presented to him.

That he willingly choses to fit props underwater without confirming the contact area of the two tapers is something between him and his customers. How he runs his business is not my business.

[fstbttms]

Originally Posted by Wotname

That he willingly choses to fit props underwater without confirming the contact area of the two tapers is something between him and his customers. How he runs his business is not my business.

Once again, having spent 25 years in the boat maintenance business I can assure you that lapping a prop is the exception rather than the rule. It is not common practice despite your attempts to make it appear otherwise.

[kenbo]

Originally Posted by fstbttms

Once again, having spent 25 years in the boat maintenance business I can assure you that lapping a prop is the exception rather than the rule. It is not common practice despite your attempts to make it appear otherwise.

I understand that you are defending your practices and ultimately your business. But I believe you're obfuscating the point of this post.

Installing a newly acquired prop without checking for adequate taper contact, either on the hard or underwater, is sub optimal at best and downright wrong at worst.

It makes not a wit how many folks you may know that don't take the time to do it correctly.

[Sailing4Jesus]

Boats are like wives. Better not to have The One You WANT than to have One You Do Not Want.

Senior Chief, United States Navy, Retired

[fstbttms]

Originally Posted by kenbo

I understand that you are defending your practices and ultimately your business. But I believe you're obfuscating the point of this post.

I am doing neither. The fact remains that (as I have said previously in this thread) the lapping of props is an uncommon practice and is (since very few props are lost and those that are typically come off because of improper installation or deferred maintenance), an unnecessary one.

You wanna haul your boat and lap your prop? Hey, knock yourself out. Me, with over 35,000 professional service events performed, have never, not once, been asked by a customer to do that.

[Wotname]

Originally Posted by fstbttms

Once again, having spent 25 years in the boat maintenance business I can assure you that lapping a prop is the exception rather than the rule. It is not common practice despite your attempts to make it appear otherwise.

Well I agree with you to a point. It is not usually a maintenance item. The devil is in the detail. A particular prop only has to be lapped once to a particular shaft, after that it can be ongoing removed and refitted without lapping it agin providing the prop and shaft remain paired.

If a shaft engineering shop supplies a new shaft and a prop you can be fairly certain it has been lapped before it left the shop - at least that has been my experience although I personally would not be happy without verifying it.

I can't speak to what manufactures do but I would be surprised if high end builders would allow a prop to be fitted without knowing the percentage contact area as part of their quality control system. Once more, this would not need to be checked again during routine maintenance. Budget builders may perhaps be less fastidious.

The issue becomes important when another prop (new or otherwise) is fitted. There is simply no way of knowing the percentage contact area inside the taper without checking with engineers blue. Sure one can take a gamble and hope it is sufficient or good enough not to cause problems but why would one when it it so easy to do it right (if on the hardstand).

IMO, saving a buck by fitting a new prop underwater and thus not knowing how good the taper fits is a poor gamble but YMMV.

[Wotname]

Originally Posted by fstbttms

I am doing neither. The fact remains that (as I have said previously in this thread) the lapping of props is an uncommon practice and is (since very few props are lost and those that are typically come off because of improper installation or deferred maintenance), an unnecessary one.
...........

Exactly - props are lost due to improper installations.

To achieve a proper installation, you have to be certain the taper contact area is sufficient. Surely this is self evident. There are several ways of knowing this e.g. it has been previously lapped correctly or the supplier has told you or you have checked it yourself etc.

However if you can't be certain and still fit it, it is by definition an improper installation.

[fstbttms]

Originally Posted by Wotname

IMO, saving a buck by fitting a new prop underwater and thus not knowing how good the taper fits is a poor gamble but YMMV.

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

[Wotname]

Originally Posted by Lifeonalean

I had a diver put this on. He used the underwater water locktite. He’s a very respected diver in Seattle known for doing prop work. I’m thinking he had to have done something wrong though but now weary of buying another flexofold because I’m unsure of the cause

Originally Posted by 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.

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????

[kenbo]

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????

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.