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Drive shaft failure |
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Wilhelm Hertzog 
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Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349 |
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 Topic: Drive shaft failurePosted: December-31-2021 at 11:33am |
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So while out on the lake late yesterday (pulling kids on a tube - in my defense, it was windy), I started noticing a pronounced vibration from the drive train and not long after that a clunk from something breaking and an immediate loss of power. At first glance it seemed to me like a transmission issue, as it appeared that the drive shaft wasn't spinning when moving the shift lever into forward despite the engine revving freely. I got a tow back, moored the boat for the night, and went back for further investigations today.
Lo and behold, today the transmission seemed to work fine. And the trans oil on the dipstick did not seem unduly discoloured, though it may have had a faint 'burn' smell. Only after the transmission seemed to work did I check under the boat: the drive shaft had broken clean off where the front of the propeller would normally sit, about an inch behind the cutlass bearing. I also noticed that the shaft anode I had fitted between the hull and the strut shortly before coming to the (brackish) lake where my boat is moored for our summer holidays was missing. I am reasonably sure we never hit an underwater obstacle in the lake, as the lake has a sandy bottom and we were never in shallow water. My conclusion is that the shaft anode somehow worked itself free from the shaft, hit the prop when it released, which then bent either the prop or the shaft or likely both, resulting in the vibration and the subsequent failure of the shaft. Fitting that anode seems to have been the most expensive preventative maintenance I've ever done. I'll probably be able to confirm my theory once I have the boat out of the water and he shaft pulled - which may be quite a while. Any other theories as to what may have happened will be welcome! Meanwhile I'll be weighing up the old 'single vs. double taper' shaft decision...
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1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer
Do not go gentle into that good night. Rage, rage against the dying of the light. |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11155 |
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Posted: December-31-2021 at 5:53pm |
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Here's something to consider It could have been fatigued long ago and survived multiple prop changes and it's time had finally come. Here's a thread from not long ago where somebody had some vibration, didn't lose the prop but came real close. He didn't have to look too hard to find the crack in the same area I had one do the same as yours for the reason mentioned above. I still miss that prop  |
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Wilhelm Hertzog
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Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349 |
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Posted: January-01-2022 at 4:09pm |
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I took good care to lap the prop to the shaft when I installed it, and made sure that the prop sat exactly where I had taped the shaft to indicate where the prop sat before inserting the key for final installation, so I thought I had minimised the possibility of fretting/shaft riding on the key. Perhaps I'll be able to establish more once I've inspected the shaft up close when the boat is out of the water (probably tomorrow).
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1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer
Do not go gentle into that good night. Rage, rage against the dying of the light. |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11155 |
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Posted: January-02-2022 at 8:56am |
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Just because you did the lapping doesn't mean that it wasn't weakened in the past and it was just waiting to fail.
The weakest part of the shaft is the keyway area under the prop, so that's where breaks like this tend to happen especially with years of use and some propeller imbalance over the years. These are different ways of saying that "it wasn't your fault" most likely And............as far as a double taper shaft............till you've used one you just don't realize how much more convenient they are
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ultrarunner
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Joined: October-02-2005 Location: Ridgefield, Ct. Status: Offline Points: 1860 |
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Posted: January-03-2022 at 12:06pm |
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Hi Wilhem, thanks for the write-up and please post some pictures of the failure area once you have the shaft on the bench.
As for Elberts' A.R.E drive shaft, they are wonderful. I did one on my previous SN, and if the shaft on my existing boat needs to come out, I'll change to one again. Ultra...
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Wilhelm Hertzog
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Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349 |
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Posted: January-04-2022 at 12:57am |
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I'll get some pictures up soonest.
In the meantime, looking at General Propeller's shaft quote form, they list three options for the alloy from which the shaft can be made - AQ17/19/22. AQ19 doesn't seem suitable for application in a Nautique, but any thoughts on AQ17 vs. AQ22? My boat does spend some time in salty/brackish water every year, but the AQ22 shaft is about $120 more expensive than AQ17. Any thoughts on whether the extra $120 is worth it? |
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1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer
Do not go gentle into that good night. Rage, rage against the dying of the light. |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11155 |
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Posted: January-04-2022 at 1:56pm |
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Here's a a link with a little more detail than the quick couple of sentences on the GP order form.
I think there's nothing wrong with AQ-19 in your application. They all (17,19,22) have advantages and disadvantages. I'd do some more reading, maybe make a phone call to GP and then go with what your gut and your wallet tell you based on your salt/brackish water usage. Maybe you've seen this thread that answers,,,,,,,,,,,,,well not much of anything, but it's some discussion anyways |
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Wilhelm Hertzog
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Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349 |
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Posted: January-04-2022 at 5:28pm |
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Thanks Ken, very informative. And impresses upon one how important correct machining of the keyway is. I'm 99% sure my shaft was cut locally, and there's a good chance the keyway wasn't cut to spec, which makes your theory of why the shaft broke where it broke all the more plausible.
Some pictures of the damage below (please excuse the terribly untidy sealant around the strut base!) - including damage to the hull from the incident:   In reading up and shopping around, the question of a flexible coupling has come up in my mind. Is it worth fitting one? Can it be fitted with a double taper shaft?
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1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer
Do not go gentle into that good night. Rage, rage against the dying of the light. |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11155 |
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Posted: January-04-2022 at 6:15pm |
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I think I'd skip the flexible coupling. If they were so good, everybody would be using them and pretty much nobody does.
I think I'm also wondering what happened to make a prop blade damage the hull that high up. Maybe like you said, the anode came off and hit a whirling blade which threw it up and did the hull damage? Based on the discoloration inside the shaft, I think the crack wasn't something new and had been there a while.
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fanofccfan
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Joined: December-13-2009 Location: North Bend NE Status: Offline Points: 1792 |
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Posted: January-05-2022 at 9:07am |
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Interesting strut. I did not know some were stainless steel.
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2004 196 LE Ski 1969 Marauder 19 1978 Ski
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Wilhelm Hertzog
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Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349 |
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Posted: January-05-2022 at 9:42am |
Not from the factory they weren't, I believe. Pete also commented on my strut in a previous thread. It was fitted by a PO, and in all likelihood fabricated locally by some engineering shop.
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1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer
Do not go gentle into that good night. Rage, rage against the dying of the light. |
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wetskier2000
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Joined: September-07-2005 Location: New Hampshire Status: Offline Points: 367 |
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Posted: January-06-2022 at 8:29am |
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Custom strut from PO, tells me this boat had a hard underwater hit before... Shaft was probably straightened and reinstalled but weakened and just waiting for enough slalom starts to finish it off like this... As Ken said, that discoloration looks like it may have been a while since the initial separation.
On the hull damage, I can easily picture that 2700 RPM prop spinning into the hull when it came free... Moral of the story? Don't pull a tube with a Nautique.
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Current: 1997 Nautique
Previous: 1987 Nautique 1964 American Skier |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11155 |
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Posted: January-06-2022 at 9:30am |
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It kinda looks like the prop had to move in the upward direction 2 or 3 inches to hit the hull on the side of the V.
That's what seems a little strange to me
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fanofccfan wrote: