2019 G23 Shaft breaking?

[MTRBTR]

Also, if that theory was correct, all inboard shafts would eventually break from simply steering the boat.

[greggmck]

I am a professional engineer. If the above theory is the case why are we not seeing a bunch of shafts break on Malibu�s and all the homemade suck gates ?

If you put the same shafts on a Malibu, installed a 17" prop, 2:1 transmission, added 3,000lbs of surf ballast and surfed the same total number of hours you would see the same percentages of failures.



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[Sailfun]

Thank you for the responses. I’m goi g to be honest this problem is enough to keep me out of the G23 for now. I cannot risk even a small percentage of that happening while on an escusions at Powell. Worst nightmare is get caught in a famous Powell storm and while fighting the caps have the prop snap off and lose power. That would be a disaster.

I would suggest you stay off lake Powell. I have owned a lot of boats and your not going to find a better built boat. There have been no reports of shaft failures manufactured after mid 2018.

[greggmck]

Also, if that theory was correct, all inboard shafts would eventually break from simply steering the boat.

Turning (or yawing) a heavily loaded boat yields much greater prop/shaft stress compared to driving straight. If this were constantly done by thousands of heavily loaded boaters for hundreds of hours you would absolutely, positively see a significant increase in shaft failures.

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[MTRBTR]

It would be interesting to get the actual forces and numbers. I wasn't saying driving straight would break a shaft. I was saying that turning any inboard (which is done a good percentage of the time) would seem to put as much or more pressure on a shaft than driving 11 miles per hour on a loaded boat with a little yawn. The placement of the shaft strut minimizes all most all of the bending moment of the shaft. Your point about the bigger surface area of the prop and basically the same size shaft does make some sense though. I think it has to do with the power from the motor, transmission combo and the shaft itself. I don't think the turning has anything to do with it. But without real numbers who knows.

[greggmck]

It would be interesting to get the actual forces and numbers. I wasn't saying driving straight would break a shaft. I was saying that turning any inboard (which is done a good percentage of the time) would seem to put as much or more pressure on a shaft than driving 11 miles per hour on a loaded boat with a little yawn. The placement of the shaft strut minimizes all most all of the bending moment of the shaft. Your point about the bigger surface area of the prop and basically the same size shaft does make some sense though. I think it has to do with the power from the motor, transmission combo and the shaft itself. I don't think the turning has anything to do with it. But without real numbers who knows.

Turning an inboard does not occur for a sufficiently long duration to be a factor in shaft failures.

I would like to see the actual numbers too. But instrumenting a statistically meaningful number of shafts with waterproof stress transducers and taking these measurements would be expensive. That said, the facts are there, staring everyone in the face. One only has to have the requisite knowledge to determine with absolute CERTAINTY that these shafts are failing because of a bending force.

A propeller shaft experiences four forces: 1) Compression, 2)Torsional, 3)Bending, 4) Tension. The compression force is the force of the prop pushing along the axis of the shaft to move the boat. It would take a MASSIVE compression force to compress the shaft along its longitudinal axis to cause it to fail. Propeller shaft failures are well studied and there are MANY reports analyzing why these failures occur. Do a google search for: Boat Propeller Shaft Failure Analysis". Compression failures almost never occur. See: https://reliabilityweb.com/articles/...and_prevention and https://www.efficientplantmag.com/20...achine-shafts/

Next is torsional force failures. Torsional force is the rotational force applied by the engine to rotate the propeller shaft. Torsional forces also occur when the propeller is rapidly shifted from forward to reverse or it strikes an object. Torsional forces cause a failure along the shafts longitudinal axis. Torsional failures have a very distinct failure mode compared to compression and bending failures. These failures are indicated by a ragged, starburst pattern along the axis of the shaft. A good way to think of this is to take a clump of dry spaghetti, hold it by the ends in each hand. Then apply a twisting force on it until the spaghetti fails. The resulting failure mode can happen anywhere along the length of the shaft and will have a jagged, angular failure profile. This has NOT been observed on any of the shafts that have failed.


Here is an image of a torsional load induced shaft failure.


Go back and look at the pictures of the broken G shafts. They ALL have a clean, roughly 90 degree failure profile. Now take that spaghetti and hold it with both hands close together, and bend your hands until the spaghetti snaps. It will fail with a relatively clean 90 degree fracture.

A clean 90 degree failure positively indicates a bending force. It will also occur right at the strut, the point of support for the bending force. Remember my example of an engine with a 10' shaft and a 500 lb weight placed on end? Where would it fail? Exactly at the point of support, in this case the strut.

I'm adding the Tension force for completeness, but clearly the shafts are not failing because the prop is placing a critical tension force on the shaft. I would hope this is obvious.

In summary, once again here is the G shaft failure picture. And there are many others in the various posts about G shaft failures. THEY ALL OCCUR AT OR NEAR THE STRUT, have a clean 90 degree failure mode, and they have all occurred because the key way was cut too long producing a weak point at the point of the greatest bending force, the strut. This is confirming evidence of a bending failure. The prop shaft is being bent by the asymmetric forces applied by the yaw of the boat and the angle of the prop shaft.

If the boat were always driven straight, the prop shaft were parallel to the water flow, this failure would never occur. But that is not the case.

[DocPhil]

Doc, you are calling BS on what exactly? That shafts have failed? 2 at my home dealer last fall alone. And that’s only those that i heard of because i saw the delivery of the new shafts when i was at the dealer so i asked about it.
Or are you calling BS that its really a concern of mine?

Im calling BS on your calling this BS haha

I love Nautique but I have a legitimate concern about this issue and the fact that over 6 years Nautique has been unable to fully mitigate the issue.

I'm calling BS on this whole thread. When you first started this thread your current boat said 2019 G23 on order. You had personal experience on prop shaft failures less than a year ago. Yet, you come in supposedly trying to learn what exactly? If Nautique remedied the prop shaft issue over winter when no one uses these boats? Then because a few people confirm that prop shafts have failed although not commonly (which you already knew), you suddenly don't want a G anymore? Like I said, I call BS.

[Tcj711]

Doc, sorry to disappoint you. But there’s no BS here. That G23 that I ordered is a true story and a long story. My dealer had 2 customers shaft break last summer after they had assured me the problem had been fixed. My business partner went though with his purchase and loves his 23. No problems in 15 hours lol. I backed out.
It’s kinda lame to doubt my doubts. I have a concern. I feel it’s a legitimate concern so I wanted to come here and ask if it’s a problem for anyone else. I’ve had a few people DM me and tell me their story of shafts breaking as well as other who have posted here. Nautique hasn’t fixed the problem and the fact they haven’t after 6 years is a problem. If it was only a 1 year problem I wouldn’t worry. So back off your BS in calling me a liar and grow up

[Neptune442]

Isn't there a 5 year warranty on new Nautiques? Buy the 2019 G because you like it, and sell it just before the warranty is up. It seems like a lot of boat owners like to upgrade after a few years anyways.

[scottb7]

Doc, sorry to disappoint you. But there’s no BS here. That G23 that I ordered is a true story and a long story. My dealer had 2 customers shaft break last summer after they had assured me the problem had been fixed. My business partner went though with his purchase and loves his 23. No problems in 15 hours lol. I backed out.
It’s kinda lame to doubt my doubts. I have a concern. I feel it’s a legitimate concern so I wanted to come here and ask if it’s a problem for anyone else. I’ve had a few people DM me and tell me their story of shafts breaking as well as other who have posted here. Nautique hasn’t fixed the problem and the fact they haven’t after 6 years is a problem. If it was only a 1 year problem I wouldn’t worry. So back off your BS in calling me a liar and grow up

I support you on this. I understand both points of view. I understand the kool-aid drinking crew that won't admit that no other brand is breaking props, or if they do they claim it is no big deal, and i understand the others that really prefer to not take the chance, or just think it is crap that Nautique hasn't really owned it. All points of view are valid...we all come from different experience sets and deal with issues differently.

[Bevostein]

You original post was targeted at the 2019 model. The answer to the question posed I think would be that there have been no reported instances of a 2019 shaft breaking. Not that I have seen at least and I think I’m pretty active at reading Nautique forums/pages/etc. Does this mean all is well? Only time will tell.

[cptotr]

Turning an inboard does not occur for a sufficiently long duration to be a factor in shaft failures.

I would like to see the actual numbers too. But instrumenting a statistically meaningful number of shafts with waterproof stress transducers and taking these measurements would be expensive. That said, the facts are there, staring everyone in the face. One only has to have the requisite knowledge to determine with absolute CERTAINTY that these shafts are failing because of a bending force.

A propeller shaft experiences four forces: 1) Compression, 2)Torsional, 3)Bending, 4) Tension. The compression force is the force of the prop pushing along the axis of the shaft to move the boat. It would take a MASSIVE compression force to compress the shaft along its longitudinal axis to cause it to fail. Propeller shaft failures are well studied and there are MANY reports analyzing why these failures occur. Do a google search for: Boat Propeller Shaft Failure Analysis". Compression failures almost never occur. See: https://reliabilityweb.com/articles/...and_prevention and https://www.efficientplantmag.com/20...achine-shafts/

Next is torsional force failures. Torsional force is the rotational force applied by the engine to rotate the propeller shaft. Torsional forces also occur when the propeller is rapidly shifted from forward to reverse or it strikes an object. Torsional forces cause a failure along the shafts longitudinal axis. Torsional failures have a very distinct failure mode compared to compression and bending failures. These failures are indicated by a ragged, starburst pattern along the axis of the shaft. A good way to think of this is to take a clump of dry spaghetti, hold it by the ends in each hand. Then apply a twisting force on it until the spaghetti fails. The resulting failure mode can happen anywhere along the length of the shaft and will have a jagged, angular failure profile. This has NOT been observed on any of the shafts that have failed.


Here is an image of a torsional load induced shaft failure.


Go back and look at the pictures of the broken G shafts. They ALL have a clean, roughly 90 degree failure profile. Now take that spaghetti and hold it with both hands close together, and bend your hands until the spaghetti snaps. It will fail with a relatively clean 90 degree fracture.

A clean 90 degree failure positively indicates a bending force. It will also occur right at the strut, the point of support for the bending force. Remember my example of an engine with a 10' shaft and a 500 lb weight placed on end? Where would it fail? Exactly at the point of support, in this case the strut.

I'm adding the Tension force for completeness, but clearly the shafts are not failing because the prop is placing a critical tension force on the shaft. I would hope this is obvious.

In summary, once again here is the G shaft failure picture. And there are many others in the various posts about G shaft failures. THEY ALL OCCUR AT OR NEAR THE STRUT, have a clean 90 degree failure mode, and they have all occurred because the key way was cut too long producing a weak point at the point of the greatest bending force, the strut. This is confirming evidence of a bending failure. The prop shaft is being bent by the asymmetric forces applied by the yaw of the boat and the angle of the prop shaft.

If the boat were always driven straight, the prop shaft were parallel to the water flow, this failure would never occur. But that is not the case.

How close to the prop hub is the support for the prop shaft? If it were closer it would seem it would help lessen the chance of a bending break. It may already have pretty tight tolerances though. I recently sold my G and can’t remember.


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[Jeb1974]

I just came across this video today - skip to 4:07. The break they show looks a lot like the one I had on our g23. I really have no idea if it’s the same issue but do find it interesting that they also had shafts breaking. https://m.youtube.com/watch?v=O8ZH8AM61uQ

[greggmck]

How close to the prop hub is the support for the prop shaft? If it were closer it would seem it would help lessen the chance of a bending break. It may already have pretty tight tolerances though. I recently sold my G and can’t remember.


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cptotr That is a VERY insightful observation. Last year I performed measurements for ACME Propellers. They sent me several propellers to experiment with to determine performance while surfing and I provided them a spreadsheet of Top Speed, Surf Speed RPM, Fuel Consumption, Sound pressure levels etc,. You can find these measurements here: https://www.planetnautique.com/vb5/f...-ballast/page2

The two propellers with the most promise for the H6Di Engine on my G23 were the Acme #3087 17.5 x 17.5 and the Acme #3085 17.5 x 17 props. In both cases these props were 17.5" diameter. Since prop diameter is directly proportional to the bending forces these propellers were manufactured with a longer 3.375" prop hub as opposed to the 3" hub on the standard ACME # 2561 17 x 17 which is shipped on the G23.

When I discussed the increased hub length with ACME (because I needed a larger prop puller tool to remove them) they said it was done to increase the contact of the propeller with the shaft and to reduce the moment on the shaft from the increased bending forces of the larger diameter props. The 17.5 x 17.5 prop was the one installed on my boat when the propeller shaft failed from bending fatigue. It had a 3.375" hub, but that was insufficient to distribute the bending forces of the larger diameter prop with the defective shaft. However, I believe that a 3.375" hub using the standard 17" diameter would be less likely to fail than a prop using a 3" hub for the reasons above. Hub length is yet another variable of why some shafts fail and others do not.

Here is a picture provided by Tallredrider of a shaft cut with the long key way and a standard 3" hub. You can see the .5" to .75" gap between the hub and the strut. You can also see the deep key way exposed up to the strut weakening the shaft at the point of greatest moment. To the best of my knowledge this long cut key way is present on ALL of the shafts that have failed on the 2018 Gs. HOWEVER, simply having this longer cut key way does not mean the shaft will definitely fail. There are metallurgy issues contributing to this failure as well. I have spoken to four owners of shaft failures and read about several on these forums. Most of the failures occur within the first 100 hours of surf use, which also confirms metallurgy defects because there are many of these shafts on boats with hundreds of hours that have not failed.



Here is a picture of the new shaft on my 2018 G that was replaced after the old one failed. There is no exposed key way past the 3" prop hub.

[greggmck]

I just came across this video today - skip to 4:07. The break they show looks a lot like the one I had on our g23. I really have no idea if it’s the same issue but do find it interesting that they also had shafts breaking. https://m.youtube.com/watch?v=O8ZH8AM61uQ

Marine propulsion shaft failures are nothing new. Do a Google search on that term and you will find over 800,000 hits. In large yachts such as the Hatteras shown in the video, the propellers are mounted as close to parallel with the water flow as possible to reduce the angle of attack of the blades and therefore reduce prop shaft bending forces. Large Yachts clearly don't have surf systems that yaw the boat and introduce bending forces on the shaft either. Shaft failures on large yachts occur primarily because of the very high torsional forces required to turn and reverse the large diameter props.

Failure analysis for prop shaft fractures is a VERY well established science. Failures are easily classified using the diagram below.



If you look at the shaft failure in the Hatteras video you will see that the fracture plane of the crack is not 90 degrees but rather angular along the length of the shaft, similar to the Torsion failure plane example in the diagram above. This confirms excessive torsional loads.

The failures on all of the G23 shafts that I have posted and the others pictured in the numerous images in these forums are 90 degree fractures. This is indicative of BENDING forces on the shaft. These bending forces occur because of Yaw and Shaft Angle of the propeller, not torsional overload.

Finally, the new G shafts are cut with a rounded end in the key way to reduce this stress point. However, I have not seen a round key yet. I suspect that might be coming soon.