2019 G23 Shaft breaking?

[charlesml3]

Cute photo. So let's see a video of you actually using it...

[GMLIII]

I am the one that has the trolling motor in my boat, as it was purchased and placed by the previous owner that lost the prop. And I would remind you that this is NOT an either/or. You are right that the trolling motor won't help in a storm. But it sure as heck will save anyone that loses a prop when their is no storm, which in fact is the point as I would wager that most of the lost props were not on stormy days.

Lets see a picture of the Skipper on his G21 stern platform operating the trolling motor. I really need a visual to comprehend.

[DealsGapCobra]

Why the bashing of the trolling motor? I sure would like to have that if something failed on my boat.


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[charlesml3]

Why the bashing of the trolling motor? I sure would like to have that if something failed on my boat.


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Nobody is bashing it. We just don't believe it'll actually work.

[GMLIII]

Why the bashing of the trolling motor? I sure would like to have that if something failed on my boat.


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I would just like to see it attached to the platform. Still can't comprehend how it would attach to the platform. If he is onto something,I'm sure others on the forum would want to see it in action . He may be onto something here for G owners

[GMLIII]

Well I guess we need to drill down on that. How do you define work? How much are you willing to wager? And what proof would you like?

Just a pictures of you on the platform operation the trolling motor attached to the platform

[GMLIII]

https://www.youtube.com/watch?v=h3pzmoVbznE

I think this is just not applicable if your on a big lake. For me on a small lake of 280 acres, my rough calculation is about half hour at 1.5 miles an hour.

Ok now I get the visual. Where do you store the wooden transom in your G21 as shown in video. I would like to see how it is designed so I can make one.

[Tcj711]

I call BS on this whole thread....

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.

[Skidave]

I don't own a G, but I can say the few things that have left me stranded were: 1) rope wrapped around the prop 2) dead battery 3) almost because of an ignition fuse 4) bad fuel pump

I'm going into my 21st year of boating. Best advice, be prepared for anything and prepare yourself accordingly.

Now, hopefully this doesn't mess up my karma for this season!

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[Tallredrider]

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 am not sure either. I think he might be calling BS on the idea that prop shafts aren't going to break anymore, but I cannot read his mind.

[Tallredrider]

I have owned 5 G23s collectively with 730+ hours. I had a single shaft failure on my 2018 G after about 80 hours of 99% surfing time. After it occurred I reached out to fellow engineer contacts in the marine industry. I learned that Correct Craft procures its shafts from three manufactures. I could only learn the names of two of them: Western Branch Metals, and Marine Machining. I then spoke to engineers in the industry and they explained why the problem was occurring. In short, the ROOT cause was a combination of metallurgy and machining. To the best of my knowledge, all the shafts that failed on the 2017-18 model boats had the key way machined well past the prop hub. This was fixed on late 2018 and later shafts. My 2019 does not have one of these shafts. And I know 6 other surfers who have 2019s Gs and I have not seen one of the extended cut key way shafts.

In summary, if you have a G23 that has a shaft with the key way cut so long that it is exposed when the prop is installed, there is a potential for the shaft to fatigue and fail at the key way. But let me be clear: Just because the key way is cut long, IT IS NOT a given that the shaft will ever fail because metallurgy was also identified as a combination in the root cause. You cannot visually inspect for metallurgy flaws.

I'm sure some will blather about the failures that occurred on the earlier model Gs. These may have been caused by the same defects but I did not research these nor learn the root cause for them. So I have no comment about why the earlier ones occurred.

Finally, I believe Correct Craft learned their lesson and has placed tighter controls on shaft production. I trust that they fixed this problem so I gave them another $160K for my 2019. Feel free to vote with your own money.

Here are two pictures. The first is of the newer shaft on my repaired 2018. Notice the space between the prop hub and the strut within the red circle. If you rotate the prop you cannot see the key way exposed at all. This ensures a stronger shaft where the load is placed between the prop hub and strut.

The second picture is of of the failed shaft. You can see the key way is cut so long that it extends to the strut (red circle).
This longer key way cut is necessary but NOT SUFFICIENT for a failure to occur.

Gregg, I thought that you had a more elaborate explanation that it was a result of the NSS? Or was that someone else? Basically, it is a little difficult to understand, but because of the drag created by the NSS, the prop essentially gets unequal force placed on the blades, causing it to break because of the unequal force.

[greggmck]

Gregg, I thought that you had a more elaborate explanation that it was a result of the NSS? Or was that someone else? Basically, it is a little difficult to understand, but because of the drag created by the NSS, the prop essentially gets unequal force placed on the blades, causing it to break because of the unequal force.

A prop sitting on a shaft doing nothing should never fail. The load placed on the shaft and the shafts ability to perform under that load are the factors to consider for understanding the root cause of such a failure. The yaw forces of NSS create an increased load on the prop and shaft than say the roll forces created by a tab based surf system used on other boats such as: Centurion, Supreme, Supra, MasterCraft, etc.

I have discussed in other posts how the 2:1 transmission, 17" prop, pitch of the boat, and yaw produced by NSS WHILE surfing COLLECTIVELY contribute to a very significant load on the prop and shaft. This was measured and described to me by engineers working to understand why some prop shafts were failing. These forces are not the cause of the failure, they are always present when surfing.

A properly designed and manufactured shaft should not fail. But some of the shafts had design and manufacturing defects that when placed under the sustained load described aboved result in a failure.

In this post I perceived a need to discuss the manufacturing factors that were addressed to resolve this failure. I did not sense a need to reproduce the detail about shaft loading yet again.

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[scottb7]

I am not sure either. I think he might be calling BS on the idea that prop shafts aren't going to break anymore, but I cannot read his mind.

Maybe it was a premonition. After the last post, I am feeling a need to call BS.

What proof do we have that NSS produces more force on the prop than a tab system? And please don't say that someone told you so. After all both systems produce same effect of convergence of the water, so it would seem the effect to the boat and prop would be pretty much the same.

The only proof would be that nautique only one losing props. But yet correlation does not prove causation. As most other mfgrs use splined prop shafts which might spread the load better then a keyway.

But I say "might" cause i really don't know...

[greggmck]

Maybe it was a premonition. After the last post, I am feeling a need to call BS.

What proof do we have that NSS produces more force on the prop than a tab system? And please don't say that someone told you so. After all both systems produce same effect of convergence of the water, so it would seem the effect to the boat and prop would be pretty much the same.

The only proof would be that nautique only one losing props. But yet correlation does not prove causation. As most other mfgrs use splined prop shafts which might spread the load better then a keyway.

But I say "might" cause i really don't know...

@Scottb7 That you ask for proof suggests you don't have knowledge of forces well understand in engineering. For example, look up "P Factor". It is an asymmetrical force on airplane propellers which results in uneven stress and it is caused by yaw or angle of attack, not roll. This is the same force that can be experienced by a boat propeller when the hull yaws or is pitched up. The key to these stressful forces are the relative flow of air or water to the propeller blades.

But let's keep it simple so most non-engineers can understand.

First is it obvious that a tab surf system causes a rolling force on the hull? Roll means the boat lists to one side, but from the propellers perspective no additional force is added because the relative flow of water seen by the propeller blades in any position remains 100% longitudinal and is the same for all blades.

To visualize this think of a torpedo operating below the surface of the water with a rudder that automatically keep the torpedo travelling straight. Paint a white line on the top of the torpedo from bow to stern. When underwater the torpedo is moving directly into the water flow and exactly in the direction of the white line. In this case the load on the propeller is the same for all blades. This symmetric propeller blade load result in a minimal and even load on the propeller shaft.

Now roll the torpedo so that the white line painted bow to stern rolls right 10 degrees but is still perfectly aligned with the direction of water flow. In this case there is still no change to the load on the propeller or shaft. Why? Because rolling the torpedo (or boat) causes no change to the relative water flow seen by the propeller blades.

Now weld a plate of metal to one side of the stern of the torpedo perpendicular to both the white line and to the direction of water flow (NSS). This plate will cause a significant drag on one side of the torpedo and the automatic rudder will have to compensate to keep the torpedo travelling in the intended direction.(This is why a Nautique requires one to always hold a significant force on the steering wheel when surfing and tab based boats with a properly trimmed rudder do not). In this case if you observed the torpedo from above you would see the white line will no longer be aligned exactly in the same direction as the flow of water. Because the torpedo will be yawing, or crabbing sideways through the water.

This is how NSS works, it yaws the boat so the stern is pushed into the surf side where the rear shape of the SIDE of the boat produces the wave.

Now back to our yawing or crabbing torpedo. Can you visualize how the forces on the propeller blades are no longer symmetric? Because the water flow on all sides is no longer the same. Blades that are moving into the direction of water flow by the induced yaw experience much greater load because the pitch of the propeller blades have greater angle into the water flow producing more thrust. Blades trailing on the opposite side produce much less thrust because the water flow is more aligned with the pitch of the blades.

With blades on one side angled into the water flow and blades on the other side angled away from water flow the shaft experiences an asymmetric force. To easily visualize this force on the shaft, image a ten foot long shaft sticking out of an engine. Then hang a 500lb weight on a bearing on that shaft. Now start the engine and spin the shaft. It could eventually fatigue if it were not designed and manufactured for that asymmetrical loading. Some shafts used by Nautique were not properly designed and manufactured for this load either...





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[MTRBTR]

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 ?