G23 Prop Fell Off .....

[greggmck]

Greggmck- good info, and great that you dug into it that thoroughly.......

I am not able to address a lot of it in depth right now, but I have a few quick points to make, because I don’t like to speak complete “nonsense”, as you said I did....

1- Take a look at all the sheared shafts...... as far as I have ever known, forged steel does not break cleanly like that. They create a much rougher break. I could be wrong about this, and I will leave that to the experts to comment. I also know that the shafts on my G had an obvious machined surface, whereas on an MC, it isn’t. I know I have tried to turn a forged shaft on a lathe before, and was not able to get a clean cut on it.... especially with the vibration you get on a shaft that length. Nonetheless, I am no expert. Maybe you can enlighten me further.....

2- A G is probably the most “bow down” surf boat ever built, so I’m having trouble believing that theory has much merit compared to the competition.

3- I have included a picture of my stock prop, and my alternate prop, from my MC. As you can see, it is an 18” prop, on a 1 1/8” splined shaft, on a boat that runs with the bow higher than a G while surfing. How is that for nonsense?!?!?

1) To learn more about forging check out this website: https://www.steelavailable.com/en/wh...steel-forging/ Furthermore, I don't know what you mean when you say "

shafts on my G had an obvious machined surface, whereas on an MC, it isn’t." as if this somehow indicates it is

forged. All shafts are machined at the prop end. Mastercraft uses a Splined shaft. By definition it is machined.

2) I don't know what measurements you have seen to state that the G is the most bow down boat ever built. All surf boats have a plate at the stern of the boat that can be used to rise the bow to create greater pressure at the stern resulting in a steeper wave with more push. This is the setting most frequently used to SURF. Skim boarders might prefer to lower the bow by lowering the plate to push the bow down. This reduces the pressure at the stern resulting in a longer and less steep wave. Every surf boat can raise or lower the bow based upon riding preference. Granted the G does have a lower gunwale in the bow. This is to improve driver visibility when in a bow high configuration. The down side of this design is that one can take on water over the bow when the ballast is full if you hit a large wave. Perhaps better visibility is attributed with a more bow down boat? But that is perception, not the angle of the hull to the water. Finally, the bow high attitude is ONE factor contributing to the failure. This factor combined with the 2:1 transmission, 17" prop, and fully loaded ballast at surf speeds ALL contribute to increase shaft loading. Many boats can have larger props, but not larger props with all of the other characteristics in a large enough sample size to experience the shaft shearing that has occurred. I believe we are talking about tens of shafts sheared in several thousand boats.

3). Stock prop on what? If you look at https://www.ozpropellers.com.au/mast...at-propellers/ The only Mastercrafts with 2:1 Gear ratios are the X20, X23. Both of these boats use the 16.0 or 16.5" props. Many boats use larger propellers than 17". But they don't have a 2:1 transmission, and push heavy surf loads too. I'm not defending this design, just identifying the factors that cause the failure.

[charlesml3]

Last owner after breaking shaft left the trolling motor in the boat. You simply hook onto swim platform, and hook up to one of the batteries. And home you go...Pretty cheap insurance to get you on your way...

So I just kept it in there. I figured if boat breaks down for any other reason (bad belt tensioner, etc.) I am covered. Pretty unlikely I would not have enough juice having two batteries...

Ha! ha! Have you tried this yet? How far do you think a trolling motor is going to push a 6000 pound boat on those batteries? I think someone stuck that trolling motor in there as a joke.

[scottb7]

Just curious how you attach the vintage 1980 trolling motor to your six figure G?

Last owner after breaking shaft left the trolling motor in the boat. You simply hook onto swim platform, and hook up to one of the batteries. And home you go...Pretty cheap insurance to get you on your way...

So I just kept it in there. I figured if boat breaks down for any other reason (bad belt tensioner, etc.) I am covered. Pretty unlikely I would not have enough juice having two batteries...

[Wayward]

Close up of hub....

[2019 G21]

Greggmck,

Thanks for the info. My father is a PE also and I was explaining this shaft failure and he mentioned the same theory as you. He also felt that the fact that the shafts break just before the prop in all the pictures could also be a sign of prop cavitation either from prop actually pulling the oxygen out of the water under heavy load causing bubbles or even little air bubbles being introduced by the hull. He saidthe bubbles would be like hammers constantly banging the propeller. I guess similar in a way to detonation in an engine,and the constant knocking taking out pistons and such.

[Wayward]

Greggmck- good info, and great that you dug into it that thoroughly.......

I am not able to address a lot of it in depth right now, but I have a few quick points to make, because I don’t like to speak complete “nonsense”, as you said I did....

1- Take a look at all the sheared shafts...... as far as I have ever known, forged steel does not break cleanly like that. They create a much rougher break. I could be wrong about this, and I will leave that to the experts to comment. I also know that the shafts on my G had an obvious machined surface, whereas on an MC, it isn’t. I know I have tried to turn a forged shaft on a lathe before, and was not able to get a clean cut on it.... especially with the vibration you get on a shaft that length. Nonetheless, I am no expert. Maybe you can enlighten me further.....

2- A G is probably the most “bow down” surf boat ever built, so I’m having trouble believing that theory has much merit compared to the competition.

3- I have included a picture of my stock prop, and my alternate prop, from my MC. As you can see, it is an 18” prop, on a 1 1/8” splined shaft, on a boat that runs with the bow higher than a G while surfing. How is that for nonsense?!?!?

[GMLIII]

Fits nicely...

Just curious how you attach the vintage 1980 trolling motor to your six figure G?

[scottb7]

Fits nicely...

[GMLIII]

Wow good stuff , thanks for sharing

[greggmck]

WHAT I LEARND ABOUT PROP SHAFT SHEARING:

Being a professional engineer for over 30 years I decided to dig into what caused the shaft to shear in my 2018 G23 H6Di with 88 hours last Saturday while surfing. I have many industry contacts and reached out to a few colleges to help me find industry experts in marine propulsion and propeller design who could provide me with a factual understanding of what happened and what can be done to remedy the issue. After a few days of asking around several people pointed me to Mike (not his real name). Mike is considered one of the industry’s best propulsion design experts and was aware of Nautique’s efforts to remedy this problem. We spoke for about an hour on this topic. He requested confidentiality so I will not use his real name or disclose the company he works for. But here is my experience and what I learned about this failure.

1. These shaft failures have occurred primarily while surfing. The loads placed on the prop and propeller shaft during surfing are much greater than wakeboarding or cruising around. While wakeboarders often use very heavy ballast, the boat is on plane while wakeboarding. A planning hull has much less drag than the same hull pushing water at slower speeds. Furthermore, while wakeboarding the boat hull is closer to level with the water surface resulting in the prop producing a more symmetric thrust. This is because both the top and bottom prop blades experience a similar angle of attack compared to surfing.

2. During surfing the bow rises higher and the bottom blades of the prop have a greater angle of attack into the water flow, resulting in them producing greater thrust than the top blades. This creates a rotational force on the prop shaft at the interface of the strut and the prop hub. See diagram below:

3. Nearly all US boat manufactures use shafts made by Branch Western Metals. These are all forged steel shafts. See: http://www.wbmetals.com/shafting.asp and http://www.wbmetals.com/downloader.a...y_Brochure.pdf

4. There are differences in shaft hardness, but increased hardness also results in increased corrosion susceptibility. Some have suggested that Nautique does not use forged steel shafts. If you believe this to be true, please provide a reputable reference because my sources say they are all forged.

5. There are several machine shops that prepare the steel shafts to make parts for Nautique and other boat manufactures. Nautique has recently switched to a new shaft manufacturer. According to “Mike” there have been ZERO failures with the new shafts but there are probably still older ones in stock at dealers. I am trying to find out how to identify the newer shafts. But I believe one clue is that on the older shafts the keyway cut can be seen on the shaft with a 3”" hub prop installed while the newer shaft is machined to have a shorter keyway completely covered by the small hub prop.

6. The reason some shafts shear close to the strut while others are a ½ or so away has to due with hub length. Some prop hubs are 3”" while others are 3.4"”. A 3.4"” hub prop has less tendency to shear because it covers the entire taper of the shaft resulting in the greatest thickness of the shaft absorbing the rotational torque of the asymmetric prop load during surfing. That said, I sheared my prop shaft using a propeller hub of 3.4”".

7. My advice. If you exclusively surf and are using one of the early deliveries of G23s (October – April) (my guess) there is a very low but real possibility you will experience a shaft shear. It will happen with VERY little warning. The boat will shutter slightly for a few seconds, then minutes later the prop will fall off and you will hear the engine rev if you are applying throttle. Mine sheared while maneuvering to pick up me while surfing. I have the GoPro recording and can post if needed.

8. You do NOT need to get in the water to know if you have sheared your propeller shaft. This is dangerous if the water is rough so avoid unless necessary. First check the neutral lock out switch. If it is not accidently engaged, lift the black cooler body out of the small cooler just in front of the engine cover. There you will see the silver shaft coupling projecting from the V-drive. Have someone put the boat in gear while you watch the coupling. If it rotates in different directions while going into forward and reverse, but your boat does not move you have sheared or lost your prop.

9. Call your dealer immediately. I called while I was on the boat, he had a shaft sent over-night to his shop and I was back on the water in 48 hours.

10. If you surf exclusively keep an anchor on your boat to prevent your boat from drifting into dangerous areas while you wait for a tow. You might want to subscribe to a boat towing service like BoatUS.com.

11. Now the 64-thousand-dollar question: Why does this happen primarily on Nautique? To be honest I do not know if other boat manufactures have experienced shaft shearing. But here is what I learned: Nautique uses a surf system, NSS that arguably produces one of the industries thickest waves with strong push. Nautique uses a 2:1 gear ratio to turn the industry’s largest propeller on a surf boat. (It was mentioned that some Mastercraft boats use an 18"” prop. This is nonsense.) See: https://www.ozpropellers.com.au/mast...at-propellers/ Furthermore, the only Mastercraft boats with a 2:1 transmission are the newer X20/X23. But both use a 16.5"” diameter prop. The combination of a 17" prop and 2:1 gear ratio will produce the greatest shaft torque. The only other boat I could find that uses a 17" prop and 2:1 gear ratio is the Malibu MXZ. I do not know if they have experienced shaft failures but there are very few of them around as a sample set too. Also very important, Mastercraft and other boats use tabs to list the boat to produce its wave. The NSS system projects out from the side of the boat which yaws the hull to create its wave, but this increases the drag resulting in greater load on the propeller / shaft. Centurion produces a similarly large wave but uses a 16.5"” propeller and uses tabs to list the hull.

It was suggested that 1.5”" shafts are the next step for Nautique, especially if the ballast on the boat is increased in future models. Personally, I would like to see this sooner than later… I hope this helps!

[GMLIII]

I think the vendor story is a fairy tale. I was hearing that back when I bought my 2016 boat.

Can a corporate Nautique guy come on here and give some answers? I'm sure they are watching.

Jeff can you get someone from corp Nautique to respond back to the forum on this issue?

[Tallredrider]

For anyone with a 2018 that has had a prop sheared...can you please add your production date / month so that we can see if the issue exists for ALL 2018s. The message about changing vendors seemed to start in October (unless someone heard earlier).

Thanks.

I think the vendor story is a fairy tale. I was hearing that back when I bought my 2016 boat.

Can a corporate Nautique guy come on here and give some answers? I'm sure they are watching.

[ironj32]

The down fall to a 2:1 transmission , 900 ft/lbs of torque a the prop with a 17 inch prop is grounds for something to break. Do you think the other companies using a 2:1 will start having the same issue?

This was an issue with the other transmissions too, not just 2:1.

[Wayward]

The down fall to a 2:1 transmission , 900 ft/lbs of torque a the prop with a 17 inch prop is grounds for something to break. Do you think the other companies using a 2:1 will start having the same issue?

Ya, no, its obviously not a 2:1 trans problem..... Bu, Tige, and MC have all been using them a while now. MC started using the 2:1 back when Nautique did in 2014.

The kicker is, MC is using a smaller shaft (1 1/8" vs the 1 1/4" that Nautique is using), and a bigger prop (18" on some models).

In looking at any of these photos of the broken shafts, its obvious that they aren't forged. Like I mentioned before, I know that MC's shafts are forged. Not sure about Bu or Tige, but I wouldn't be surprised.

I honestly have no idea why Nautique wouldn't have upgraded to a forged shaft as soon as they saw this issue start 4 years ago......... Only logical explanation would seem to be that the thick headed engineers are wanting to place blame elsewhere, and not have to replace a couple thousand shafts at $300.00 each. Probably rolled the dice in the beginning, and hoped it was fairly isolated. That doesn't seem to be the case though.

[Wake.BC]

The down fall to a 2:1 transmission , 900 ft/lbs of torque a the prop with a 17 inch prop is grounds for something to break. Do you think the other companies using a 2:1 will start having the same issue?

Tige has been using 2:1 for a couple years, so has Malibu with the raptor engines.


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