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Go Back   SailNet Community > On Board > Gear & Maintenance > Broken shaft....and what else?
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Thread: Broken shaft....and what else? Reply to Thread
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Topic Review (Newest First)
07-07-2010 11:55 PM
Pub911 A couple thoughts that are very remote, but haven't been mentioned so here goes in an effort to save you some hauling charges if the situation, by chance, is less severe than a broken shaft.

When you did the 'you turn your end while I hold mine still' test - were you certain to be grasping actual shaft on both ends? or is it possible one person was grasping a zinc, strut, prop or other anscilliary appendage? If you're uncertain, repeat the test - you can do this on a short haul and may even be able to do it while in the water.

If it truely is broken, not only are you going to have to replace it, you're going to want to determine the cause. I've seen a bronze shaft crack like a twig when it struck a log - but only after years of use without proper zinc protection. The pitting was so severe the entire matrix of the shaft was comprimized. SO the lesson is, be sure your zincs are working.

I will repeat for emphasis the importance of alignment - even in a v-drive. a simple check on this is to eyeball the attitude of the engine side prop shaft end relative to the transmission coupling while taking the shaft throu a "+" manuever in the shaft log. this will require removal of any stuffing box or similar device, and it's not an alignment process as much as it is a test on whether the alignment is WAY of of whack. IF it is, it will be very clear to you the at one or more of the 4 endpoints of the "+" motion (up to stop, down to stop, starboard, port) you will notice that the travel does not leave the shaft equidistant from the coupling - if this is true, it's likely to be your root cause of the break. That said, it would be very surprising that a loud noticiable noise or vibration underfoot would not have been experienced prior to the damage.

good luck.
07-07-2010 05:56 PM
stiffwind Thanks Harbin2, it sounds like my shaft may have met the same fate as yours. I am still uncertain whether there is some kind of coupling or universal joint in the shaft between the stuffing box and the transmission that could have become disconnected or broken, but if not then it appears the fracture occurred to the part of the shaft to the aft of the suffing box flange and just forward of the through hull.
07-06-2010 07:55 PM
harbin2 Mine broke 2 months ago. I sailed 45 miles home and my marina got me in my slip. The repair cost was $3K including haul out and in. My shaft is only 3/4" and mine is a direct drive. I posted here and concluded the primary cause was alignment - fatigue failure. The new shaft is Aquamet 22 (supposedly the best steel for shafts). I have no idea what the old shaft was made of. Also, I have a dripless shaft seal that was made before they came out with the vent tube. The break was inside the seal so I do believe the heat in the area of the seal contributed to the break. Your situation is lots more complicated than mine so I don't believe this info. really helps you.
07-02-2010 04:37 PM
EpicAdventure If the shaft is broken, don't you worry about the whole shaft sliding out, thus leaving a very large hole in the bottom of the hull?
07-02-2010 03:41 PM
stiffwind
shaft problem

Hey Bill and the others at Sailnet who responded:

thanks for all your thoughts. I have never taken apart a Yanmar 3GM transmission or shaft components so I am not sure if I explained the set up accurately. But it does seem that many more esperienced sailors are also puzzled by the circumstances. I have not had an opportunity to investigate further because I had to abandon my trip and return home. When the shaft is pulled this coming week I will report back with more details so that we all might get some insight as to what went wrong.
07-01-2010 10:41 PM
btrayfors
Quote:
Originally Posted by stiffwind View Post
Hey Bill, folding prop seems to be working properly. Could overtightening the stuffing box cut through a shaft in just 15 hours of running? something sounds unusual here.
Well, anything's possible given the vagaries of alignment, corrosion, and initial build quality as others have mentioned. But, I have to say, it does sound weird to me. I've had two boats with three v-drives over the past 27 years, and have worked on lots of others. It IS hard to align them, but even when alignment isn't perfect I've never seen a broken shaft result.

Overtightening the packing nut could cause excess heat, but....

Guess when you pull the shaft you'll have a better chance at diagnosing the problem.

Good luck,

Bill
07-01-2010 06:27 PM
T37Chef I'll take a guess...

When was the last time you checked the alignment?

V Drives don't allow for much variance. If the shaft has been bent due to poor alignment it may be possible it finally gave way. I read tons of info this year about shaft alignment and drive-train components when I was dealing with similar issues. As strange and odd as it sound, I read about 1"+ shafts breaking from poor alignment. I did read about the crevice corrosion that SD speaks of but everything I read directed the cause being shaft seals like the PSS (I believe the reason they now have the vent tube installed?), you stated you have a traditional stuffing box. (not disputed you SD, just say'in)

Also, when was the last time you replaced the engine mounts?
Did you notice excessive vibration or noises from the transmission/engine?
Do you have any oil leaks in and around the rear seal?
07-01-2010 06:13 PM
tommays From what i have seen and repaired a LOT of shafts are NOT lined up correctly when installed causing stress


I have heard to many tales here of a shaft that will not turn free after doing nothing but replacing the cutlass bearing
07-01-2010 05:57 PM
stiffwind Hey Bill, folding prop seems to be working properly. Could overtightening the stuffing box cut through a shaft in just 15 hours of running? something sounds unusual here.
07-01-2010 05:54 PM
stiffwind I see the shaft turning in both forward and reverse from the and the gear box mechanics seem to work fine in and out of gear. I first thought it was prop prob. but then dove on her...first put her in gear...and turned the prop even though in gear. That test suggested broken shaft. After I hauled her, we could turn and pull the shaft while somebody was holding the shaft inside the cabin engine room...it wasn't moving, thus one end wasn't attached the other.
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