Bent shafts

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DickTuschick
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Bent shafts

Post by DickTuschick »

OK....I'm going to share a "hot issue" on the shafts used on the PDQ 34.
Recently we have encountered two boats with both shafts bent. A 2004 and a 2005 boat.In all four cases the "bend" was very similar in magnitude and location.
As you all know from previous posts, shaft alignment has been an issue in a lot of boats. The boat yard where these repairs have been made has advised us that it is highly possible that the out of alignment situation and the resulting "wobble" that is caused has eventually led to a permanent bend in the shafts.
Taking the shafts out and having them straightened is a fairly simple but expensive process that can be avoided by proper alignment.

However, alignment is often not totally understood by everyone and I asked the boatyard to provide a better explanation:
Shaft / Engine Alignment. There are two planes of alignment, axial and radial. Most boat mechanics understand only radial alignment. Radial alignment is accomplished by loosening the coupling bolts which hold the two halves of the coupling together (the shaft half and the gear box half). The gap along the circumference is measured, and the engine moved by adjusting the mounts until the gap is reasonable equal at all points around the circumference. But the situation may be made worse if the axial alignment has not been verified first; a bit more difficult with ability as well as understanding.

Axial alignment is the straight line path of the shaft through the cutlass bearing(s) and shaft log to the centreline of the gearbox coupling. Only when this has been established will a radial coupling alignment result in reasonable accuracy.

So....if when running the boat you see a noticeable vibration in the shaft and dripless shaft seal, there is a high probability that you need to check engine alignment and possibly the shafts for straightness.
I'll certainly be watching my shafts very closely !!!
Bargain Bill
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Re: Bent shafts

Post by Bargain Bill »

The physics makes sense. I have 2 questions:
1. Who does the axial allignment ?
2. Must the boat be hauled ?
Bill & Fran Carlson
Easy Riders MV34 #029
Ocean City, MD
duetto
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Re: Bent shafts

Post by duetto »

DickTuschick wrote:In all four cases the "bend" was very similar in magnitude and location.
dick, can you describe further the size and where the bends occurred.
john & diane cummings
duetto mv34 #23
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Captnautigal
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Re: Bent shafts

Post by Captnautigal »

I noticed a 2007 34 had aqua drives installed. Was this PDQs attempt to solve the long ongoing problems with leaking
Shaft seals? The fact that the 34s shafts are only supported by the cutlass bearing in the stern tube with no forward struts and are only supported by an engine with cushioned mounts seem to make them prone to this problem which will only worsen as the boats age.
Maureen (Captnautigal) and David
Catatonic - #74
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Captnautigal
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Re: Bent shafts

Post by Captnautigal »

A few more questions regarding these shafts, vibrations, etc. (our boat is currently on the hard dealing with this warped shaft issue). I reported a problem with leaking shafts and vibration issues a few months back. We had the engine alignment checked when this first came up . This was done in the water. It is my understanding that engine alignment should be done in the water since boat flex can make a difference in the alignment out of water. The engines and shafts were within tolerances - they were aligned. When we hauled the boat we had the shafts pulled to see if they were bent and make sure they were aligned straight though the cutlass bearing to the engine. The cutlass bearings we installed 2 years ago were worn uneven, the shafts were not traking straight to the engine. I spoke with Dave Mayo, from Tides Marine, at both the Fort Lauderdale and Miami boat shows. I found out that Tide Marine would not warranty their seals in the PDQs because of too many failures. Much has been written on the seals in the forum. Tides Marine feels vibration is the culprit. Dave from Tides has been very helpful. I asked if 4 bladed props would help this type of vibration. He said 4 bladed props would help with performance but not with this leaking seal situation. He suggested checking the shafts as well as the engine mounts. Too much vibration from the engines will cause the seals to fail . That is why I've asked the question regarding the Aqua drives. I have since searched the forum and noticed a few have installed Aqua Drives. I'd like to know if anyone had problems with failing seals after that upgrade. The comments I did read, reported significant reduction in vibration. I just wonder if having the support on the forward part of the shaft would stop the "sag" resulting in "bending" caused by the current configuration.
Maureen (Captnautigal) and David
Catatonic - #74
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Captnautigal
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Re: Bent shafts

Post by Captnautigal »

Catatonic is back in the water. Stuart Yacht did a great job with our shafts. We had them removed from the boat. They were sent to the shop to be examined and ultimately straightened and recondidtioned. Much care was used in reinstalling the shafts making sure everything was in proper alignment. The cutlass bearings were changed and they also added half bearings in the forward portion of the stern tube. They measured the length of the shafts and this additional support is half way to the engine coupling. This helped keep the shaft aligned as it came through the tube to the back of the engine. We also installed new red Tide Seals. Dave Mayo from Tides Marine and Gregg Burdick, Stuart Yacht, talked at length about the PDQ shaft issues. Both are excited to see if the second bearing will assist in keeping the shaft aligned and stop the bending, which, my understanding, is a result of the whipping action under the current configuration. We also plan on installing aqua drives on our next haul out. We ran the boat on and offshore to the Keys from Stuart. She was noticably smoother - especially at idle speeds. The work we have done at Stuart Yacht is always exeptional and first rate. It's great meeting all the other PDQ owners that are being serviced there as well! Already starting our wish list for our next visit!!!
Maureen (Captnautigal) and David
Catatonic - #74
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