Problem with shroud attachment

[Jim Fulton]

I'm overhauling the mast on my 1975 Bristol 34: removing and reinstalling all of the fittings using Tef-Gel and UHMW tape, running new electrical wiring, etc. I am almost finished with the mechanical work, and I have run into a significant problem with the fitting that connects one of the upper shrouds to the mast. Each shroud is fastened to one of these fittings with a clevis pin. The fittings are attached to the mast with a 1/2" bolt that goes through the mast. This bolt appears to take the load from the shrouds. In addition, each of the fittings is further fastened to the mast by four 5/16" screws. The only function the screws appear to perform is to keep the fitting in position. The problem is that the threads in one of the screw holes have been weakened, probably by corrosion, to the point that a screw will go into the hole, but it cannot be snugged down tight.

I see two alternatives: One is to ream out the holes in the fitting and the mast, and to replace the one 5/16" screw with a 3/8" screw. The other is to do nothing. Presently, the 5/16" screw holds in the hole, but I can't tighten it enough to compress the lock washer. However, any load on that screw is in shear, so nothing will be working to pull it out. On the other hand, I don't like the idea of a more-or-less loose screw at the top of the mast.

My inclination is to go with the 3/8" screw. Does anyone have any other ideas?

Jim Fulton

[captinkid]

The only other thing I can think of is using a SS pop rivet in that location. It does not rely on threads to achieve a solid hold.

[Brion Toss]

Hello,
The stainless rivet will work, and will be fairly strong in shear, as well as secure laterally. Hard to remove, though, and not as strong as a screw. A stainless helicoil installation might be preferable. Easy to install, and quite strong. Or a Riv-Nut could work: a blind rivet with a threaded interior. You set it in the mast with a specialized tool, then install an ordinary machine screw. Nifty.
Any of the above will work, and in deciding, it might be good to begin by analyzing what the screw is supposed to do. In this case, it and its fellows distribute the shroud load to more mast molecules, taking some of the load off that bolt. For this reason, doing nothing, and just letting the current screw float in its corroded hole might not be the best course, as it won't -- quite -- bear a full share of the load. Plus, as you mention, there's always the possibility that it will fall out someday.
Fair leads,
Brion Toss

[Jim Fulton]

Thanks for the ideas. Here's what I finally did: There is a similar fitting on the other side of the mast. I removed the corresponding screw from that fitting, and ran a 5/16" bolt through the mast connecting the two. Easy, quick, cheap, and it probably strengthens both sides. It was an alternative that was obvious after someone else suggested it.

Jim Fulton

[Matthew Sebring]

The only real concern with a bolt passing through the mast is that you don't overtighten it. Time after time after time we've seen bolts that have been tightened to the point that they are pinching in the mast. Also, if you have internal halyards you want to make sure that they aren't abraiding on that new bolt.

[Jim Fulton]

All of the shrouds--lowers as well as uppers--are anchored by through-bolts. I replaced all of them as I was rebedding and refastening the mast hardware. There are no internal tubes or other reinforcements in the mast to prevent over-tightening, and I was struck by the potential for damage. I used lock nuts, and tightened them only to the point where the associated fitting is secure and the bolt and nut assembly does not rotate easily. All my halyards are external and all wiring is in a conduit, so there is internal interference.

Jim Fulton

[Matthew Sebring]

Sounds like your probably ok. With the through bolts the tangs hang on I sometimes use locknuts but generally either stake the nut or most often drill the nut and pin it in place with a small cotter pin. This is to ensure that there is really only one position where things line up correctly and so hopefully later down the road well meaning people with wrenches don't just tighten it like crazy. Of course I also make sure that the threads themselves aren't bearing on the extrusion - just solid shank.