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Can rivnuts fix my mast?

Printed From: Yachts and Yachting Online
Category: General
Forum Name: Repair & maintenance
Forum Discription: Questions & tips on the subject
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=11516
Printed Date: 04 Oct 22 at 1:37am
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Topic: Can rivnuts fix my mast?
Posted By: Wobble
Subject: Can rivnuts fix my mast?
Date Posted: 16 Jun 14 at 5:01pm
I have a Flying Fifteen mast (Selden, about 10 years old) on which the holes for the spreaders rivets have enlarged, leading to wobbly spreaders with (potentially*) unpredictable consequences. 
The holes aren't huge, but they are big enough so that the head of a rivet capable of getting a grip in them is too big for the awkwardly shaped spreader attachment fitting, even after filing down the fitting.
Determined not to shell out for a new mast -- I'm tight, unlike my spreader -- I'm wondering if anyone has had experience of and, hopefully, success in using rivnuts or even rubber rivnuts in this situation, and would welcome any advice on going about the task, especially without having to buy a rivnut tool for the sake of two fixings. 

* The amateur engineer in me actually is not convinced that the spreader moves when the rig has tension, as this tends to force the fitting back into place in the mast. Two other rivets on the opposing part of the fitting (not the opposite spreader) are sound. Maybe I'm being too optimistic, but the boat performance hasn't been affected, yet... If there were an effect, I would expect the boat to beat better on one side than on  the other, and that hasn't happened. 






Replies:
Posted By: JimC
Date Posted: 16 Jun 14 at 5:38pm
Can you not simply ream/drill the spreader bracket out for the next size up rivet?
Don't understand what you mean about the rivet head.


Posted By: Wobble
Date Posted: 16 Jun 14 at 6:07pm
Nope. I've already opened it up as much as I can. There's a part in the way... a raised section that connects to the adjuster screw. This is the part which I have already filed to well below original thickness. If I ream/file any more, that will be compromised. 


Posted By: craiggo
Date Posted: 16 Jun 14 at 6:41pm
I would say a rivnut would work but the external flange would need to be large enough to seat in the bracket but small enough not to clash with the bracket features you mention. I haven't used any for sailing, but you'd need to be pretty careful with material selection.
I've had a few boats where the spreaders have been bolted on. You need to thread some line through the bolt holes in the mast, then tie the line to the end of a bolt and pull it through. Make sure the bolt is overlength put the bracket on then add the nuts. Use some mole grips to hold the bolt and torque the nuts up. When done cut the bolt down to length. This would work on your boat assuming you can get the nut to fit. It's bloody fiddly though.


Posted By: piglet
Date Posted: 16 Jun 14 at 7:43pm
What material rivnut? Stainless will erode the hole further, ally might be too soft and plated steel will make 'orrible mess.
Are you already on 1/4" pop rivets? Will they fit in the space?
Craiggos suggestion of mousing bolts through might work, bloody fiddly though.
I've effectively repaired Laser booms by cutting a segment piece from another tube, sliding it inside, then drilling & riveting through the old holes into the new patch piece.
But that sounds worse than bolt idea.


Posted By: JimC
Date Posted: 16 Jun 14 at 7:46pm
You can't cut back part of the rivet head to miss the raised section I suppose? Bearing in mind its larger than the original you could probbly get away with some lost area. I've not come across these rivnuts before: they look intriguing for some tasks, but like craiggo I worry about electrochemistry. Reckon you may be stuck with trying his bolt on a string trick. Arm yourself with lots of patience!!


Posted By: timeintheboat
Date Posted: 16 Jun 14 at 9:00pm
When I had the same problem it was as per Craiggo. Mast up against the side of house, up a ladder up next to the mast, very fine thread tied into the bolt thread, pointy nose pliers and a fair degree of swearing. The mast broke elsewhere later, it is in my garden with the spreaders still very securely bolted to it.

-------------
Like some other things - sailing is more enjoyable when you do it with someone else


Posted By: Wobble
Date Posted: 17 Jun 14 at 12:49pm
In reply to JimC...

No -- it's not just the rivet head but the rivet gun that won't go in there. This isn't such a problem for soft rivets but I have found that the harder ones (can't remember their name) are much more inclined to snap off before fully closed in. Also, the rivet size is limited by the hole in the fitting, smaller than that in the mast. 
Rivnuts would get around that problem as the rivnut size would  be bigger than that of the bolt going into them.




Posted By: Wobble
Date Posted: 17 Jun 14 at 12:51pm
I think that the cautions outlined above probably are pointing in the direction of Craiggo's bolts and a long-noser. Otherwise it looks as if I might be pioneering the use of rivnuts for this purpose, and I'd prefer someone else to do that experiment!

I can do fiddly stuff as I have been know to lose halyards etc up there before -- just resign to taking an afternoon to do it -- and I can do ffluent swearing too, so it seems I am well-armed to take on this task. I assume the bolt also takes a washer on the inside? 


Posted By: transient
Date Posted: 17 Jun 14 at 1:18pm
....some Duralac might be good as well. It'll add the extra frustration of messiness.


Posted By: piglet
Date Posted: 17 Jun 14 at 8:21pm
Monkey goo


Posted By: sandgrounder
Date Posted: 18 Jun 14 at 4:12pm
Originally posted by Wobble

I think that the cautions outlined above probably are pointing in the direction of Craiggo's bolts and a long-noser. Otherwise it looks as if I might be pioneering the use of rivnuts for this purpose, and I'd prefer someone else to do that experiment!
I can do fiddly stuff as I have been know to lose halyards etc up there before -- just resign to taking an afternoon to do it -- and I can do ffluent swearing too, so it seems I am well-armed to take on this task. I assume the bolt also takes a washer on the inside? 




I have done a lot of these over recent years, preferring the security of M5 A4 stainless steel bolts over pop rivets on every occasion. I use an A4 stainless washer on the inside, and also a nylon washer, with the nylon washer closest to the mast. To assist in pulling the bolt through the hole I find it helps to taper the end of the bolt using a Dremel and abrasive wheel, and I use 6lb fishing line.



Posted By: Wobble
Date Posted: 18 Jun 14 at 5:15pm
Thanks sandgrounder for that excellent advice. Hadn't thought of using a nylon washer. 

Forced to wait a bit to do this job now, as I have discovered on taking it off that the spreader lug is cracked thanks to previous efforts with rivets, and I need to get a new one. Really want to get back on the water now but I'll have to be grown-up and deal with delayed gratification. 

Will post hopefully positive outcome here when done...


Posted By: Wobble
Date Posted: 02 Jul 14 at 5:02pm
Got the job done at last!

Incredibly fiddly, as predicted, and a little compromised.

In the end I  used the spreader hole to get inside with a lead mouse, stood the mast up and rattled like hell, exiting via the spinnaker uphaul sheave hole; then pulled in reverse so that I was able to pull the bolt out the hole and into place. Sounds easy but it took forever because I started with the wrong method -- trying to drop the bolt directly from the jib sheave above because I hadn't though it through properly and just went for the biggest entry point. Head-wrecker.

In the end, no ladders or platforms needed. But next time will definitely heed advice to use stronger fishing line, and also more highly coloured. Dull brown, lightweight line was the biggest cause of distress, with one bolt lost -- temporarily -- up the mast due to a break. (I am now doubly fluent in swearing and general crankiness.)

Bolts (6m) are a bit undersized for the hole due to the limit on the lug, and I could get only one nut on each bolt because of the shape of the lug and the need to leave room for space for the securing pin for the bottle adjuster, which still needed a bit of gentle hammer-persuasion to fit home.

Couldn't find nylon washers, but I did use Duralac and it got everywhere. Also used threadlock on the threads to help the nuts, now dead tight, stay in place. I'll need to monitor them carefully... here's hoping!

I hope this account helps anyone considering a similar operation. Thanks again to all for the very sensible advice.

PS: I was thinking when preparing at one point to fail with the bolt method (desperation being the mother of invention)... Would it make sense to pull a washer against the inside of the enlarged hole, then superglue it in place to give a new, smaller hole to fit the usual-size rivet? Also fiddly, but I think it could work generally where rivets are preferred but the hole has become too big.


Posted By: piglet
Date Posted: 02 Jul 14 at 5:18pm
Well done Wobble, I don't think the blood vessels in my Cerebral Cortex would have put up with that.
 
Your idea of pulling up a washer on adhesive for later pop riveting has some merit.
Though I would go for a scavanged piece of ally in place of the st.st. washer and epoxy or methacrylate in place of the superglue.
 
You realise it will break next weekLOL


Posted By: Wobble
Date Posted: 03 Jul 14 at 10:43am
Good idea on the scrap piece. If it all falls apart next week, I'll give that a go -- after my therapy sessions. 


Posted By: Ian29937
Date Posted: 04 Jul 14 at 11:43am
Originally posted by Wobble

In reply to JimC...
No -- it's not just the rivet head but the rivet gun that won't go in there. This isn't such a problem for soft rivets but I have found that the harder ones (can't remember their name) are much more inclined to snap off before fully closed in. Also, the rivet size is limited by the hole in the fitting, smaller than that in the mast. 
Rivnuts would get around that problem as the rivnut size would  be bigger than that of the bolt going into them.



Have you tried putting a couple of small nuts on the shaft of the pop rivet. This moves the riveter away from the fitting and as long as the riveter still grips the shaft, it gets around the problem of interference from the fitting.

Cheers

Ian


Posted By: Wobble
Date Posted: 04 Jul 14 at 1:12pm
Never thought- of that Ian. Brilliant suggestion and will give it a go next time, which hopefully will be a long way off!



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