Cardude close call on crossing

[BruceK]

..Here is the last remaining bolt that was trying to hold the thing together. If you look closely the threads are smashed in the middle.
View attachment 123042

I had the transmission replaced on this boat a few years ago and I think they reused the same bolts, so I’m assuming this is the OEM bolt...

Put the last remaining hero which saved your bacon in a glass display case,for people to come and see.

 

[cardude01]

I’ve reached the regret phase of my adventure. I realize now that it was an overly ambitious run for my level of preparedness. I thought the 7 day run through the ICW before we reached the Gulf crossing would be enough to check the boat out and make sure it was ready, but I really didn’t check things out well enough. I fixed some nagging autopilot issues during the ICW time, but I didn’t pay enough attention to other things.

 

[AZ2Loop]

I’ve reached the regret phase of my adventure. I realize now that it was an overly ambitious run for my level of preparedness. I thought the 7 day run through the ICW before we reached the Gulf crossing would be enough to check the boat out and make sure it was ready, but I really didn’t check things out well enough. I fixed some nagging autopilot issues during the ICW time, but I didn’t pay enough attention to other things.

Cardude, I suspect you are being a little too tough on yourself. There will always be something else one could have checked. This is now one thing you will always keep an eye on (and maybe a few more of us will do the same). That's good. We do the best we can, but there will always be something else.

 

[diver dave]

Dude; but u are having an adventure!
most of us are at home NOT having an adventure. [emoji41], and keeping our failures at sea a secret.
Rather making you, brave and adventurous!

 

[angus99]

I'm going to do the same

Folks, I strongly suspect one of the root causes of shearing of the shaft bolts would be misalignment of the engine to the prop shaft.

Good thought, but in my case the packing was new and the alignment had been done by very reputable yard with the boat in the water.

And to clarify, my through-the-shaft Grade 8 bolts sheared (multiple times) AFTER the transmission was properly re-bolted to the housing. I’m going to try Ski’s recommendation to torque to Grade 8 specs and see what happens.

good to know all you need is two right?
attention to detail is one thing, but forgetting to do the main thing is something else.

Yeah, I’ve found several other shortcuts and half-assed approaches that have accumulated over the years. I’m continually amazed at the abuse these old Lehmans and running gear can absorb without breaking down.

 

[cardude01]

Seen that happen a bunch of times. Coupler bolts shearing. Most common on boats with tight access to that area where the last tech could not (or did not) get enough purchase on the bolts/nuts to get enough torque on them. Can hear the muttering "good enough". A few years later, it was not "good enough".

Gotta put the hoodoo on those grade 8 bolts/nuts. Whatever it takes, wrench-wise.

What is the proper torque for these bolts?

 

[Ski in NC]

What is the proper torque for these bolts?

What gear, what engine? What is the diameter of the bolt hole? Not sure that was even the right bolt for the job.

I will PM you my phone number.

 

[cardude01]

What gear, what engine? What is the diameter of the bolt hole? Not sure that was even the right bolt for the job.



I will PM you my phone number.

Thanks Ski

 

[O C Diver]

I’ve reached the regret phase of my adventure. I realize now that it was an overly ambitious run for my level of preparedness. I thought the 7 day run through the ICW before we reached the Gulf crossing would be enough to check the boat out and make sure it was ready, but I really didn’t check things out well enough. I fixed some nagging autopilot issues during the ICW time, but I didn’t pay enough attention to other things.

Don't beat yourself up. We all make mistakes. Few are willing to be open about our bad experiences.

Two take aways to your credit:

You had a viable plan B.

You were able to effect repairs based on skill level, available tools, and parts.

I'm sure you will repair the failure to industry standards before your next adventure. Combining all of the above puts you in the top 5% of owner operators.

Ted

 

[Ski in NC]

Kanzaki KM5A looks like the flange bolt holes are 12.3mm dia, so a 12mm bolt will work. Flange thickness 12mm. So if other flange is same thickness, total of 24mm, room for nut and lock washer prob add another 12mm. So 36mm?? Maybe bring four 35mm and four 40mm and use what fits best. Either class 10.9 or 12.9 will work.

What is length of the bolt that lived?

Looks like plenty of room fwd of flange for what sticks out of nut. From dwg looks like about 15-20mm.

Bolt torque depends on strength class and thread pitch. Easy to look up on line.

 

[C lectric]

Sorry about your troubles. What an ordeal. I'm just glad you made it to safe harbour.

 

[diver dave]

While on the topic of things falling apart at the coupler, i have a story.
Had just arrived in the bahamas after crossing; i see the aft bilge pump squirting quite a stream and not shutting down.
On that boat, i had instant access via deck hatches to the stuffing boxes. I should say PSS shaft seals. Suspecting bellows failure, i looked at the rush of water. Not from a torn bellows, but from the bellows not making contact with the wet bearing at all!
The shaft had moved within the coupler, separating the two sides of the seal. Then, i recalled backing down during a fish fight just before, about as hard as ever. I jumped into the water and jumped on the wheel to push the shaft back in.
I learned about drilling dimples for the coupler set screws that day.

Now cross drilling thru the shaft is another matter altogether. A real loss of strength there i would suppose?

 

[BandB]

I’ve reached the regret phase of my adventure. I realize now that it was an overly ambitious run for my level of preparedness. I thought the 7 day run through the ICW before we reached the Gulf crossing would be enough to check the boat out and make sure it was ready, but I really didn’t check things out well enough. I fixed some nagging autopilot issues during the ICW time, but I didn’t pay enough attention to other things.

No regrets. You failed to check something that likely a majority would have and you had the spares to repair it and did so at sea. Pretty impressive to me. And a lesson learned. Definitely not something I see to regret and I'm pretty tough on those I feel are over their head.

 

[Blissboat]

The Dude knows something about adventures in yachting. Very glad this one ended okay, but it must have had you all pretty shaken up for a while! Thanks for sharing enough that the rest of us have learned from your experience.

I've known of shafts that sheared under way, including one that split and tried to disappear out the shaft tube, 'til the prop fetched up against the rudder and jammed the steering. That was on a party fishing boat full of passengers about twenty miles offshore.

Coupler bolt failure is a new one on me, but as soon as I read this, I realized - why not? Another d@^n thing to think about while underway offshore at night, listening to the propulsion noises . . .

 

[HopCar]

“ I've known of shafts that sheared under way, including one that split and tried to disappear out the shaft tube, 'til the prop fetched up against the rudder and jammed the steering”

Had that happen to me when I was in high school. I had a 16’ Bahamian built dinghy with a 10 hp Palmer gas engine in it. I was towing a string of optimus prams in after a race. It was an international race and most of the kids didn’t speak English.

All of a sudden the rudder jammed and the engine raced. I shut it down and jumped over to take a look. Sure enough the prop had slid back into the rudder. I shoved the rudder aside, pulled the prop and shaft out, and held them up for my buddy to see. He of course started shouting “Put it back! Put it back! We’re sinking!”.

We had an outboard kicker hanging on the stern so we were able to get the kids back to the yacht club.

 

[O C Diver]

So were sheared off bolts found or did the nuts all loosen?

One of the things that is often overlooked is the condition of the lock washers. In new condition they should bite into the nut and flange. Probably a good idea to replace lock washers each time for the negligible cost.

Ted

 

[Max1]

I’ve reached the regret phase of my adventure. I realize now that it was an overly ambitious run for my level of preparedness. I thought the 7 day run through the ICW before we reached the Gulf crossing would be enough to check the boat out and make sure it was ready, but I really didn’t check things out well enough. I fixed some nagging autopilot issues during the ICW time, but I didn’t pay enough attention to other things.

Actually, I for one am grateful that you shared your experience with us.
Being a new (big) boat owner, I am paranoid of having a catastophic failure on my boat and not being prepared. Until this post, I not once have ever considered this as a possibility and like others here, would not have thought to inspect the propsaft bolts.

Now that I am aware of this risk, I resolve to add the checking and inspecting these bolts to my annual pre & post season inspection checklist, as well as keeping an eye on it during the boating season. I also learned from your experience to make sure I have adequate spares on board to be able to handle unexpected breakdowns. Thanks for sharing a good lesson. As they say in the aviation world: "Learn from others mistakes. You'll not live long enough to make them all yourself" I love this expression for its double-meaning. The second and more sinister meaning is that you will kill yourself very soon if you don't learn from others. Being new to big boats, I want to ensure I have a long and prosperous boating life

 

[psneeld]

Hey guys...no need for panic.

While this isn't unheard of, it isn't common either.

Make sure your bolts are in good shape and properly torqued and 10 years down the road they may need checking again....but by then, tranny or damper preplacement may cause a normal inspection/ replacement as necessary.

Lots of other stuff to be sure of too.

 

[cardude01]

Kanzaki KM5A looks like the flange bolt holes are 12.3mm dia, so a 12mm bolt will work. Flange thickness 12mm. So if other flange is same thickness, total of 24mm, room for nut and lock washer prob add another 12mm. So 36mm?? Maybe bring four 35mm and four 40mm and use what fits best. Either class 10.9 or 12.9 will work.

What is length of the bolt that lived?

Looks like plenty of room fwd of flange for what sticks out of nut. From dwg looks like about 15-20mm.

Bolt torque depends on strength class and thread pitch. Easy to look up on line.

Thank you Ski

 

[cardude01]

So were sheared off bolts found or did the nuts all loosen?



One of the things that is often overlooked is the condition of the lock washers. In new condition they should bite into the nut and flange. Probably a good idea to replace lock washers each time for the negligible cost.



Ted

On the one bolt that remained the lock washer was smashed pretty flat, so that was part of problem I assume.

I was only able to find one bolt in the pan under the engine, and it was sheared near the nut.

 

[Island Cessna]

Or, it could be that I’m just a general dumbass. ?

Here is the last remaining bolt that was trying to hold the thing together. If you look closely the threads are smashed in the middle.

View attachment 123041

.

You might consider aircraft grade bolts. https://www.aircraftspruce.com/categories/aircraft_parts/ap/menus/ha/bolts.html They have a longer unthreaded “grip length” that might delay disaster if they loosened, they are fine threaded, and are good quality. Available drilled if you would like to lock wire. Buy the matching AN nuts and if you want, hard washers.

PS: after posting I noted that Cardude’s bolts were metric….. not sure above applies, but there are lots of Inch sized prop flanges around. I doubt my 1967 vintage Velvet Drive has metric bolt holes!

Bill

 

[PaintMeRetired]

If coupler bolts are coming loose it’s being caused by something and I suspect alignment. A coupler face that isn’t exactly 90 degrees to the centerline of both the drive shaft and transmission output shaft will alternately expose the bolts to tension and then compression 1/2 rotation later. It will also be putting cyclic loads on the transmission bearings and that gets expensive- quickly.

 

[sbman]

If coupler bolts are coming loose it’s being caused by something and I suspect alignment. A coupler face that isn’t exactly 90 degrees to the centerline of both the drive shaft and transmission output shaft will alternately expose the bolts to tension and then compression 1/2 rotation later. It will also be putting cyclic loads on the transmission bearings and that gets expensive- quickly.

If this was the case, a connecting rod bolt/nut in an engine would never hold together. The tension/compression forces here are miniscule compared to other uses of nuts and bolts. You can easily bolt up two flanges that are not perfectly aligned, the shaft just bends to accommodate. While that certainly isn't desired and causes a number of issues, it won't cause the nuts to come loose.

The physics behind a shaft coupler flange demand tight nuts and bolts. The bolts provide a clamping force on the two faces of the flange, face to face, and this clamping force must be maintained. The two flange faces being tightly clamped together provide friction that lock them together rotationally, the bolts are not designed to be used as 'pins' in the rotational direction of shear.

If nuts/bolts become loose the bolts are being used as shear pins through the holes instead of providing the clamping force and can be sheared by the torque impulses applied to them during operation, assuming they don't fall out first, round out the holes they are in, etc...

 

[diver dave]

If this was the case, a connecting rod bolt/nut in an engine would never hold together. The tension/compression forces here are miniscule compared to other uses of nuts and bolts. You can easily bolt up two flanges that are not perfectly aligned, the shaft just bends to accommodate. While that certainly isn't desired and causes a number of issues, it won't cause the nuts to come loose.

The physics behind a shaft coupler flange demand tight nuts and bolts. The bolts provide a clamping force on the two faces of the flange, face to face, and this clamping force must be maintained. The two flange faces being tightly clamped together provide friction that lock them together rotationally, the bolts are not designed to be used as 'pins' in the rotational direction of shear.

If nuts/bolts become loose the bolts are being used as shear pins through the holes instead of providing the clamping force and can be sheared by the torque impulses applied to them during operation, assuming they don't fall out first, round out the holes they are in, etc...

well done; and you a SW engineer?

 

[sbman]

well done; and you a SW engineer?

A buddy of mine, a mechanical engineer did a paper on this very phenomenon, albeit in relation to aircraft prop flanges. He created a solution using belleville washers to maintain clamping force through a much wider range of bolt/nut tightness profiles. This was after his propeller departed the aircraft in flight one afternoon due to loose nuts/bolts and he really rather that didn't happen again.

 

[Southern Boater]

Seen that happen a bunch of times. Coupler bolts shearing. Most common on boats with tight access to that area where the last tech could not (or did not) get enough purchase on the bolts/nuts to get enough torque on them. Can hear the muttering "good enough". A few years later, it was not "good enough".

Gotta put the hoodoo on those grade 8 bolts/nuts. Whatever it takes, wrench-wise.

Happened to me recently, finding one shaft moving laterally while the other perfectly level, found the polyflex flexible coupler, transmission side bolts finger tight!

After checking PO’s maintenance records, “mechanic” had done alignment work and even described on the invoice, coupling bolt removal…….maybe it was an extra charge to do them back up again?!

 

[catalinajack]

Happened to me recently, finding one shaft moving laterally while the other perfectly level, found the polyflex flexible coupler, transmission side bolts finger tight!



After checking PO’s maintenance records, “mechanic” had done alignment work and even described on the invoice, coupling bolt removal…….maybe it was an extra charge to do them back up again?!

Those "flexible" couplers are worth doodly. I fractured one just running strongly in reverse. Out they came with a stainless spacer installed inn its place. Allowed for a more precise engine alignment. I HATE DriveSavers.

 

[skyhawk]

way back in the early 1990's I did a deep dive on this topic....although not related to marine applications. It's why I brought up alignment earlier in the thread....

I was an engineer at a papermill and used to oversee a laser shaft alignment program (among other things including a vibration analysis program), I went to a week long school and learned to teach our mechanics how to use the laser shaft alignment system, etc... I'm pretty sure all that stuff now is plug and play simple but back in those days it was "heavy" stuff.
I have long ago forgotten the tolerances we used...but it did depend on shaft rotation...most of our stuff was rotating 1,200 RPM, 1,800RPM, 3,600 RPM...but we did have some slower stuff too.
Anyway, the various types of couplers we used would have their own spec of how much misalignment they can handle...and it was often quite a lot. Our spec standards were much tighter because even though the coupler might be able to handle the vibration, it would do damage to the machinery that it was driving and to the motor driving the shaft. I suspect this is something behind the difference of opinion between sbman and paintmeretired.

 

[Wanemardo]

I'll make this a short story version ref an experience crewing a sale delivery of a BVI 50' Beneteau 10 year charter veteran. We were motorsaling, just more than half way between the Turks and Caicos and Georgetown, Great Exuma, ~2:00 AM while off watch I heard the engine speed up and then back to cruise rpm, assumed the on watch had bumped the throttle lever.
Maybe half hour later, the fun started when the offwatch opens the cabin door, and announces we had to have a meeting(?), and I smell something hot, like wire insulation!
Seems upon investigation, we find the coupling has separated from the engine, has slid aft and is now rotating against the plastic rubber shaft log (OEM Beneteau part). Ummm, guys, stop the boat, or at least maintain minimum steerage (7kts vs 1 kt). We manage to pull the shaft forward, off the shaft log seal, lash it to prevent any movement, and sail on to Georgetown.
Next day, all four bolts are missing, and we find 1.5 bolts, so this has been a 1 bolt connection for sometime from the looks of the other coupling hole!
We find a NAPA store with 7 bolts, and 5 nuts, so I bought'em all for spares!
Back to the boat, we pull the shaft the rest of the way to the trans coupling, and guess what? there is an 1/8" top gap when the coupling's bottoms touch. Think we have an alignment problem? yes we do... we end up raising the engine front mounts ~1/2", and the couplings align as good as its going to be with improvised feeler gages Horizontal and vertical look almost perfect. Engine power tested, no visual or measured run out, and less vibration than before the final failure. Yes, this was a McGuivered repair, but it was the best we had under the limited circumstances.
Postmortem:
Engine coupling alignment was the root cause of our failure. that last metric bolt showed long time fatigue cracking before the shear/tension final failure. The bolt half we found had similar markings. The mis-alignment apparently caused a cyclic tension on the bolts as the top of the coupling's halves were continually pulled apart at the top at every turn of the shaft. (if the bolts were properly torqued, one could suggest the bolts then would be above torque design limits.) Fatigue failure can happen in thousands or millions of cycles, until there is a failure.
Suggestions: Check alignment, monitor engine mounts, check a bolt/all bolts
By the way, the coupling was metric (French built Beneteau), and I could only find ASME course thread bolts at the NAPA store.
And last I heard; those bolts were still in service! ;-)
And a big shout out for the locals in Georgetown, first thumb out hitchhiking got a ride into town, or call a cab on Ch 16, those Napa store guys were great. I'd go back there anytime.

 

[psneeld]

Several experts have posted here before on engine alignments and the reality, depending on how soft your boats engine mounts are..the engine is constantly in and out of alignment depending on motion and power applied...maybe more but I a not the expert.


Sure get it as close as possible...but exacting isn't really important if in normal tolerances and unless it is atrocious probably not as big a factor in failures as other issues.