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Hello,

We sailed our new (to us) Pearson 34 home from Newport RI to Boston MA over the last few days. This is our first boat. Our one heartrate-raising moment was finding we had no forward or reverse drive just after exiting the cape cod canal. I don't want to think about what would have happened if this occurred 20 minutes earlier while we were IN the canal.

Anyway, the quick diagnosis was that the prop shaft coupling came unbolted from the transmission. I found all four bolts and reconnected them and we made it home. I will check alignment now that we're in our home port but we didn't notice any vibration at all after the repair.

I don't know if the marina where it was winter stored loosened these when they hauled it, or if the bolts just backed out by themselves. In any case, it's on my check-list of things to continually check!

I was wondering what the opinions are on the various flexible couplings out there. These look interesting to me R and D MARINE : Flexible Shaft Couplings We have a volvo MD2030 (not sure offhand which penta transmission)

Anyone have bad/good things to say?

Thanks so much in advance!

Bob

ps: here is the blog of our trip:
Fujin Voyages 2010: The Trip Home
 

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What were the nuts/washers on the coupling? Was it a locking setup or not? The only coupling bolts that I have seen come undone were non locking nuts with flat washers.
 

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Discussion Starter #3
No nuts or washers. The hex head bolts thread directly into the transmission coupling. I actually wasted a bit of time looking around for nuts and washers under the engine before I realized the disc itself was threaded. I was surprised to see no locking mechanism.
 

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There should at least be lock washers. Even better is having the bolts wired so they can't back out.
 

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I would agree that there should be lock washers under the bolt head.

Sorry, I don't have experience with flex couplings in marine applications so I can't help you there.
 

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Change the bolts and they should be hardened steel. It is likely they took a lot of stress banging around until they fell out. Properly torqued they should not come loose. Never seen it before. The only flexible drive I ever used was a Scatra Drive. It was a constant velocity coupler with dual planetary u-joints. I installed one over 30 years ago when I did an A4 Yanmar conversion. It worked great and eliminated all vibration and alignment was not important anymore. It was expensive, required about 6" of space and a new bearing mount. Pretty much overkill for an existing application.

Gene
 

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Hi Bob,

Given what you describe, changing the shaft coupling is not going to solve the issue or make a difference. The bolts had come loose, or someone was in the middle of repairs and did not tighten them properly. On my Pearson 10M with the Atomic 4 I had the same kind of setup, the coupling bolts screwed straight into the coupling on the transmission side. However never had any problem of loosening bolts.

I would agree with the suggestions made above. Get Grade 8 or better bolts of the same thread. They should be machine threads and most likely fine threads. Whatever type they are, you will have to match the threads that are on the Tx side.

I would say keep an eye on them once you replace them with proper bolts and keep a spare set handy. Since you cannot use locking nuts you may think about using a blue Loctite (DONT ever use red for this application). However I would think about it before you do. It is sometimes quite difficult to remove the bolts after using blue Loctite...:)

Hope that helps.
 

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Bob,
I agree with Gene T & Sea Fever, the old bolts no doubt took a beating. I have used blue Locktite for many years on many different applications and can't remember any fittings that came loose when Locltite was properly applied. Never had any problems taking things apart with it although some times a little extra pressure was needed to start un-screwing things, but, IIRC, never snapped any bolts off. Short of safety wiring, which requires drilling the bolt heads in addition to cramped quarters, the only other things I can think of are really aggressive lock washers, which with blue Locktite should do the job.
Also, the Locktite may help prevent rust from forming on the threads. No affiliation with Locktite, just a long time satisfied user.

Dabnis
 

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We had the same thing happen to us using a flexible coupling on our first cruise taking our boat from the launch facility to our home marina.

The flexible coupling was old and apparently brittle. I decided to check how the boat did in reverse before pulling into the marina. We were right at the last channel marker going into the marina. We had no forward or reverse; it was too windy to sail in against the wind and river current. I threw the anchor out before drifting out of the channel and called tow boat. We replaced the coupling and I keep the rubber coated in silicone now.
 
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