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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 07-01-2010
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Broken shaft....and what else?

Lost propulsion in the mid-chesapeake, sailed on for 2 days without power, but that got old quick sitting outside your destination in calm winds.
Apparently, have a broken shaft in a Passport 37. Standard stuffing box set up. How bad will this repair be? and what likely caused a 1 1/4 steel shaft of break? Is it a sign of other problems
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Old 07-01-2010
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Chances are very good that the shaft broke from crevice corrosion if it is stainless steel. This is a pretty common issue with stainless steel shafts if they're the wrong alloy.
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Old 07-01-2010
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thanks for the thought. With my reverse V-drive set up it must have broken between the stuffing box flanges and the hull, so it seems that the stuffing box is implicated...never noticed any vibrations etc. I'm just not understanding how you break a 1 1/4 inch steel bar without any warnings, and without any adjacent torque
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Old 07-01-2010
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How do you know it's broken? You said, "apparently".

Loose coupling? Loose or missing prop? Bad transmission or V-drive?

Did you actually see the shaft end that goes into the V-drive turning with the engine in gear?

BTW, I agree with you...it's not often you see a broken 1.25" shaft unless there has been some major stress...like running up on rocks at full speed :-)

Bill
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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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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.
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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
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Old 07-01-2010
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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?
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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
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Old 07-02-2010
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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.
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