need advise on gooseneck bracket bolts

Rick Webb · Jan 27, 2007

Rivets That Large are Not Unusual

It's just that you won't find them at Ace Hardware and the tool to set them is a couple of feet long.Cut a 3/4" hole in the front and put bolts thru each hole with a nut on the otherside? Or a threaded backing plate maybe.I like the rivnut idea too.Donald, ask a rigger out there what he thinks a solution might be.

Moody Buccaneer · Jan 27, 2007

It's FUBAR

Come on people. Look at where the bolts are. They are on the side of the mast. Look at the diameter of the bolts and the thickness of the section. The section is 3/16" thick at best.Sorry, but the installer screwed up big time.The bolts appear to be 1/4 or 5/16. You need at least 3 full threads for an acceptably strong fastening. 1/4-20 gives 3.75 threads, 5/16-18 gives 3.375, you can safely go from 1/4-20 to 5/16-16 in 3/16 material. If the bolts are 5/16 now, any oversize will be weaker. 3/8-16 give a theoretical 3.0 threads in 3/16" but that's really pushing it when you are looking at an eroded spar.First mistake was fine thread. Second mistake was no insulation on initial install (I'll wager that the fitting has never been off the mast since it was installed). If is has been off, the last person to install it should be keel-hauled.

It's not clear is the mast is being refinished or the gooseneck fitting. If the mast is being refinished, it is out of the boat and more than one repair option is available.If the mast is being refinished, why weren't the damaged threads caught at the time of dis-assembly? If the threads are gone, there is also probably erosion of the surface under the gooseneck fitting.Depending on the condition of the mast around the holes the two options I would consider are; plug weld the holes and re-drill using UNC threads, or clean up the holes slightly oversize and install a threaded backer inside the mast.When any SS fitting is installed on an aluminum spar, it MUST be insulated. That means a gasket, or a layer of tape, or a coating of liquid neoprene. All fasteners MUST be coated with an electrical insulator like Lanocote or Tef-Gel.Robert has it right, yet gets argued with. Some of the "advice" on this thread is why professional riggers *hate* DIY "repairs".BTW it is sound engineering to install Heli-Coils as part of a design. Harken does it on their stuff all the time. Lewmar installs Heli-Coils in their larger winch bases during manufacture. The Heli-Coil has more surface area to spread the load. The tensile strength of a bolt threaded into aluminum is limited be the surface area of the threads. Installing a Heli-Coil increased the tensile load of the bolt without requiring a longer bolt and deeper threads.Fix it right, if the mast hasn't been out of the boat within the last five years, it's time to pull it and do a good service anyway. Once the mast is out a proper repair will be easy.

RAD · Jan 27, 2007

I think Ross

Has come up with a great solution with the Nut Inserts, Rivet Nuts, and Rivet-Type Studs seems like a simple solution and do you think a Helicoil will grab the material if you went that route

Ross · Jan 28, 2007

Rivet nuts were designed to allow machine screw

threads in thin stock. Helicoils are made for restoring threads in thick material and as inserts in new aluminum parts that must receive threaded fasteners. Both systems require special kits for installation.

Moody Buccaneer · Jan 28, 2007

RivNuts

RivNuts are indeed an option. However there is a learning curve to install them and they require a special tool to set them properly. I know from experience that RivNuts can be quite fussy, particularly when installed in tubing or on a curved plate.Permanent repair could be fabricated using common hand tools. A 5/8 - 3/4 x 3/8 bit of 6061 flat bar could be drilled and tapped to act as a backing plate. Once the mast is out, it should be no big deal to get the backing plate into the mast and aligned with the holes. You might even be able to fish it into place through the halyard exit.Once in place it can be held with the gooseneck fasteners while the mast and backer are drilled and tapped for 8-32 flat heads to hold the backer in place when the gooseneck bolts are removed. Spray the gooseneck bolts with cooking spay (Pam works well) and thread them into the backer just far enough to fill the threads. Repair any eroded areas with a Structural Epoxy filler and let set. Remove the bolts, the cooking spray acts as a release agent. Sand and fair the filler.Now you have known good high tensile threads at the gooseneck. You have spread the load over a greater area of the mast. You have created a barrier to further erosion. The repair is stronger than the original installation.How tough is that?

Ross · Jan 28, 2007

Moody Buc, That backing plate is a good

scheme but I would glue a stick to it with hot melt glue or masking tape and have someone maneuver it while I put the bolts in place.

Moody Buccaneer · Jan 28, 2007

Tag line

Faced with that repair on a mast still in the boat, I would run a tag line from the halyard exit to the top hole on the gooseneck fitting. Put the tag line through the top threaded hole and drop the backer into the mast through the exit hole. The tag line will bring the backer to the top hole and it should hang close enough to get the bolts started so I can proceed with the repair.I use this method to through bolt mast fittings where the wall thickness is not large enough to tap to a larger size. It also works to reinforce boom vang and mainsheet bails on light booms.I'm not a big fan of riveted fittings on masts (although many masts are built that way from the beginning). I much prefer threaded fasteners whenever possible. You have me thinking about RivNuts. It might be more economical for our customers in the long run than drilling and tapping the holes. If the threads get damaged, the RivNut could be replaced in about the same time as it takes to drill out a rivet and replace it. It would certainly make routine maintenance and inspections easier. Now I have to do a cost/benefit evaluation ... thanks for bringing it up!

r.w.landau · Jan 28, 2007

Then again a 5/16 x 24 bolt would give you,

good thread through the mast and still be done with out compromising.Yes, a backer plate is always the way to go, but it is over kill.The mast has been fine until now. The added bolt diameter would give you a great shear ability than that which was currently there.The 5/16x 24 is not really that fine a thread.I am saying it would be a fine fix. Yes the backing would be stronger but with what was there is it needed?Those rivet nuts are interesting. I may try to find some and order a few just to look them over. I have seen solid versions for wood but not for metl. Ross, sorry I didn't see your rivet nut post....No comment

Donald, as you see this forum can come up with good ideas, now the decision is yours.I think Moody's idea with the predrilled and pretapped plate and a 3' long string 1/8" or so, with a knot in the middle and put it through the upper hole, pulled tight and then when secured with a few of the fasteners the line could be pulled back out, is the strongest solution. If there is mast deterioation around the old holes, this would eliminate problems retapping the holesr.w.landau