Clunk ... Aaahh! ... Crunch

Went out for a three-hour cruise in Carquinez Strait today to exercise the JD, with the benefit of a seal swimming in Mare Island Strait paying no attention to us and the "neighborhood" trawler collecting fish bait, as well as an eagle catching a fish in Carquinez Strait.

Well, entering my berth at the Vallejo Marina, about three-quarters in, I shifted from neutral to reverse to check forward momentum. Then CLUNK, the sound of metal hitting metal! The shift to reverse had no effect, so the 14-ton Coot hit the dock. No damage as speed was slow. Boy, do I have an attentive Guardian Angel! Hate to think it could have happened elsewhere.

After inspection, I found the cause. Can you all propose/guess the cause of my dilemma?

prop came loose? shift cable broke or came off
Steve W

I had a similar experience in my ill spent youth. Clunk, bam, and the rudder locked. Yup, broken prop shaft. How about you?

Probably the shaft broke and the prop and what was left of the shaft slid back to the rudder. Lots of years of fishing string and crab trap yellow line build up.

If the shaft didn't break, did it pull out of the engine coupling?

HopCar said:

I had a similar experience in my ill spent youth. Clunk, bam, and the rudder locked. Yup, broken prop shaft. How about you?

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Damn you type faster than me.....

Swampu, great minds think alike, but I bet we're both wrong.

You're getting very close. Will answer this evening (PDT).

Key come out of the keyway?

I can't imagine you broke the shaft at idle...I don't know what your drive train looks like...coupling bolts?

OK. Here it is.

A two-foot section of the propeller shaft, connecting the transmission with the remainder of the shaft, came apart SIMULTANEOUSLY at both forward and aft universal joints. Glad it didn't come apart at just the aft end, resulting in the shaft section whipping about.

The shaft, it's gone!



The shaft section was "resting" on top of the hull. Here I've placed it along the shaft astern.

Mark, you're a lucky boy that it happened when it did!

Scary stuff. How about a close up photo of the point of failure?

Baggiolini said:

Mark, you're a lucky boy that it happened when it did!

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Yes! Thanks to my Guardian Angel!

HopCar said:

Scary stuff. How about a close up photo of the point of failure?

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Looks like all of the devices holding the universal joints together came "unattached."

If you find out what caused this-- poor manufacturing, substandard material, defective casting or machining-- it would be interesting to know. Seems an odd occurance on a brand new boat. Or did fasteners simply loosen up and fall out? If they did I assume they were not safety wired?

I'm writing this from the Delta airport lounge at Narita on our way to Beijing for a couple of weeks. So since we're on the other side of the dateline I guess I'll get your response before you write it.

interesting we were just discussing this very same setup in another thread....I'm guessing the same setup that reduces vibration.

one view of safer boating is that boats should be as uncomplicated as possible to keep failures at a minimum and others believe that some complication reduces failure (both mechanical and human) to a degree.

here's an example of good workmanship to a point (install) and I'm sure good maintenance and routine observation of gear...but yet.. a what I would guess is a VERY uncommon failure happened...probably up there with getting hit by lightning.

so the debate will continue...neanderthal for reducing failures...or material progress for making boating incrementally easier, safer, more enjoyable, etc...etc

Thank you for the post Mark...this is where forums shine as it is info that is rarely heard )even better seen) from manufacturers, dealers, "experts", etc.

I'm eagerly awaiting the "why" it happened for the back of my mind, boating hard drive.

That sort of coupling with thrust bearing arrangement, which is great at preventing vibration, v's the old straight shaft arrangement most of us have, really shouldn't come apart any more than one would expect the tail/drive shaft on your car to do so. Less likely, in fact, as subjected to much less speed variation and intermittent stress. It looks like all the bolts in the two universal joints came out at once. However, in all probability they have been loosening for some time, then one came out altogether causing enough stress to account for the others rather more quickly. Still - should not have happened. Especially on a near new boat. Guess who is going to become the most paranoid checker of his prop shaft universals in the boating world from here on in....?

I'd like to see some close up pictures of the failed parts. I designed and manufactured steering shaft u joints for 25 plus years and failures like that are rare.

markpierce said:

Can you all propose/guess the cause of my dilemma?

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That assembly is a Cardan shaft. It appears that the pin retainers loosened or were never tightened properly when installed and were probably missing for some length of time until one moved out enough to create sufficient vibration to throw both out.

My guess is that the engine end pin left the scene first and the clunk you heard was the prop flinging the shaft around which caused the aft pin to depart. If it happened in the reverse order you might have had an even more exciting adventure.

This is a case study in why "checking" moving parts means to actually look at them and move them to make sure all the bits are in place and fastened properly.

jleonard said:

I'd like to see some close up pictures of the failed parts. I designed and manufactured steering shaft u joints for 25 plus years and failures like that are rare.

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Cardan shaft failures are not all that rare in marine applications. Alignment is just as critical as other shafts and careful attention to fasteners is important. It is not a "fit and forget" item.

RickB said:

That assembly is a Cardan shaft. It appears that the pin retainers loosened or were never tightened properly when installed and were probably missing for some length of time until one moved out enough to create sufficient vibration to throw both out.

My guess is that the engine end pin left the scene first and the clunk you heard was the prop flinging the shaft around which caused the aft pin to depart. If it happened in the reverse order you might have had an even more exciting adventure.

This is a case study in why "checking" moving parts means to actually look at them and move them to make sure all the bits are in place and fastened properly.

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something that is absolutely necessary...but I'll be the first to admit that long list of checks gets shortened with time...

when I used to deal with cardan shafts used in Ag equipment the bearing cups were held in place by spring circle clips which fit into a groove in the "yoke". If the bearing cups were not pressed in completely the clip wouldn't seat into the groove and sooner or later the "cross" and shaft would come loose. Could be what happened here
I had never heard of cardan shafts being used in a boat, but it does seem to be an application which would make engine alignment less critical. A good thrust bearing would be required.

Steve W

I didn't know that had setups like that in boats. Mines a shaft with a huge coupling. The motor is positioned at a down angle and has a variety of shims. U joints would be nice. I would imagine you have a cutlas bearing? Might want to check that as well. I second some close up shots. Good post though.

Shew! Close one, Mark. It sounds suspicious. I'd have difficulty believing it was a material failure of some kind. Likely, it was something that was missed in the final check. It could have been a real disaster if, like Rick B. noted, it didn't come apart as it did.

RickB said:

This is a case study in why "checking" moving parts means to actually look at them and move them to make sure all the bits are in place and fastened properly.

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Who would thought the universal joints would come apart? Seems the pins all came out. I am presently tied up at home for the next couple of days while a new heater and air conditioner is installed. Won't get back to the boat 'til the end of week.

markpierce said:

Who would thought the universal joints would come apart?

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If it is made of two or more parts assembled by humans or machines and is subject to movement, vibration, temperature changes, or manipulation - intentional or otherwise - it will come apart sooner or later.

RickB said:

That assembly is a Cardan shaft. It appears that the pin retainers loosened or were never tightened properly when installed and were probably missing for some length of time until one moved out enough to create sufficient vibration to throw both out.

.

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Rick-- Are these pin retainers something that would normally be safety wired, like the set screws (bolts) on our shaft couplers?

It is unlikely to be safety wired since there isn't much control over the weight and a Cardan shaft should be dynamically balanced.

It is probably an automotive or agricultural version the builder adapted to drive their boats. Some higher quality units use a two part yoke that is bolted to hold the cross or pins in place, some (as this one appears -only Mark can tell without posting one of his usual large photos) are budget versions that rely on the bearing retainers to hold it together. As someone else mentioned, a split ring and groove holds each bearing in place. Some use a cap with a single central bolt to retain the bearing and locate the assembly.

Thanks. I can now visualize the components that are being talked about here (I think). Seems very odd that at the low rpms we're talking about here that the forces would be great enough to break them or throw them out of their housings.