interesting failure- dyneema rig terminal

[MicHughV]

btw....I'm a big fan of the WEST system. When I built my boat, I used a lot of it. It's remarkable stuff. WEST has additives for most anything you'd ever want.

[Patrick of M]

Fwiw, joining/repairing curved surfaces with a patch metal + epoxy + rivets/screws etc is a pretty great combination. Hard to calculate the strength, but I've done some pretty cheeky repairs that held up.

[pcmm]

From what I see in the original and the "repair" there problem still hasen't been addressed. The lever arm that is built into the design of the saddles. In an effort to make the saddles "mass produceable" you've given up the stability and load bearing capability needed. The bolt shouldn't really need to have significant tension on it to do its job. Most mast tangs are actually bolted loosely so that the tang can self align. The design in post # 52 is the most logical way to fix your engineering errors.

[SV Confianza]

Originally Posted by kenbo

You may be treading a fine line there, inexpensive vs safe.

When you say Atlantic Beach I assume you mean NY, not NJ. If you need professional help with that repair across the NY bight in NJ on Cheesequake Creek is a very competent yard called Lockwoods. But they'll definitely cross the inexpensive line.

Can't add much to this one other than the rigger that lockwoods uses does not work with dyneema, so there's no professional opinion to be had there.

[Sailer_Med]

Much better design this iteration! The bend moments are reduced significantly. However with a 1.26 safety factor in the assembly, I offer these remarks as refinements that will help hold every thing together.

Referring to the items in the attached sketch....

1) 10-32 fasteners are going to have marginal thread holding in the mast if the drawing is representative of the actual thicknesses. Remember the rule of thumb: thread engagement needs to be 1.5X fastener OD to begin have full strength. This application looks like 1x fastener OD or maybe less. Use good fasteners from a credible source.
2) Aluminum is maybe not a good idea for this plate. These components are subject to cyclical loading. I would be concerned that the sheeves would hobb into the Al plate over time. I'd use steel.
3) Scab plate. In order to generate the predicted clamping forces consider bonding a scab plate inside the mast that will be drilled and tapped during the assembly. This lets you get well over the 1.5X fastener OD for thread engagement. With a scab plate you also relieve the constraint that was probably pushing the design to 10-32 fasteners.
4) The 5/16-11 threaded rod is worth re-thinking. Can you get a 3/8-24 or even 1/2-20 through there if you open the holes up? I would go with fine threads in any case 5/16-24 and use AN fasteners from a credible source. No SS here, there are many mfgr of crappy SS hardware around. I wouldn't use all-thread rod in any case.

[RaymondR]

1. Make the ferules (browny-red bits) from alumilium.

2. Make the cheek plates from aluminium and longer. Curve them to flush fit against the mast side.

3. Make matching plates for the inside of the mast.

4. Weld the ferules to the aluminium cheek plates.

5. Bolt through the cheek plates, mast sides and inner plates.

6. Go sailing confident that the rig will continue to stand up.

[pressuredrop]

Originally Posted by Sailer_Med

An idea, half baked, yet maybe useful to consider. Doesn't change the loading, however, it does change the location at which the load is applied significantly.

Not half baked. This is a great solution.



THIS PROBLEM IS A DESIGN FAILURE NOT A DYNEEMA RIGGING FAILURE!!!!!!!!

[MicHughV]

Regardless of the many technical suggestions made here for repair, this mast needs to come down to affect those.

Trying to affect repairs with the mast still standing up, will risk personal injury for those involved.

[neilpride]

I assume seeing the idea to repair it, that the halyards run external?

[markxengineerin]

The mast appears to be OM3D here
Cruising Mast & Boom Assemblies
I have about 4.5" of "flat" to work with on the face before the mast starts to curve.
Wall thickness .156", not much. These numbers are different (in the wrong direction() than my old CAD so I will update. I will use a torque wrench to do a torque to strip test on 10-32 fastener, don't have one onboard at the moment. Scab plate is a good idea thought, I will consider.

There is no 5/16 threaded rod, if I said that somewhere it's a typo. It's 5/8-11 thread. All the fasteners are going to be grade 8 steel. I will keep them painted or Tefgelled or both, and keep an eye on them. They're 20 feet up so hopefully will see less salt intrusion.

3 halyards are internal, as is a bunch of wiring, I will have to make it fit, and round all edges.

Another rough day in the anchorage, gusts heeling the boat over, very cold hands. I was able to get a better look at the damage before it became unbearable. There is no deformation above the fitting. Below, over-estimating, 3.75" of dented in material

Above, only about 3/4" of space to the spreader boss weld in the tightest spot. Not much room for fasteners where I would like to put them.

[Patrick of M]

Above the fitting is that a raised boss or distortion damage?
I liked the internal scabbing idea posted earlier but think in your position I would consider it overkill, as the repair would require cutting into the mast for insertion.
If I was short on cash, I would make reinforcement aluminum plates about 10" long, curved to the profile of the mast as best I could. I would use epoxy and screws to initially bind it to the mast, then add a bunch of aluminum pop rivets, and remove screws(chafe machines).
I agree with others the outer bearing needs to move inward, so I would make up a tang supported by the through bolt, with 2 bearing points below one for each shroud, also illustrated in a previous post .
All this could be done with hand tools, other than perhaps the bearing surface (cheeky tang?) for the dyeema, although an electric drill in a vice can serve a a primitive lathe, and using a grinder and sandpaper/files, decent rounded shapes are possible.
p.s. if there is a boss not distortion around the bolt hole, maybe thicker aluminum plate, hollowed out to clear the boss, everything filled with epoxy.
I have made similar stressed area repairs using this technique, I was sceptical, but surprisingly these repairs held up

[kenbo]

Originally Posted by SV Confianza

Can't add much to this one other than the rigger that lockwoods uses does not work with dyneema, so there's no professional opinion to be had there.

Correct on the rigger but I was referring to the mast repair. I was assuming he could work the dyneema himself.

[markxengineerin]

Above the fitting is a boss (it's the tip of the original compression post), no distortion up there. The boss itself is cracked and distorted and definitely needs replacement, and the area below it buckled in. The buckling is worst right below the hanger, and tapers back to normal unaffected surface within 3.75 inches down as noted w/ the sharpie. Photo from when I originally bolted this stuff together shows the boss a little better


I am thinking that any plate weak enough for me to bend to the mast form isn't going to be strong enough to support the loads, so prefer a thick flat plate bolted and glued to the mast. There also isn't any damage to the curved mast surfaces, just the flat face. Hoping to avoid chafe on screw tips by making them the right length, no stick out.

[Patrick of M]

That is a helpful picture. Didn't realize the mast was flat, that will definitely make a repair simpler. Definitely think you need to get the shroud bearing closer to the mast or the leverage will bend you repair. Dynamic levering is powerful stuff. Looks like you could modify the black bits as stand alone.
Re screws, the problem with correct length screws is that they are difficult to start in a glue up situation as you want them to have a pull in/clamp function initially. That said, with a multi screw set-up, get a bunch of overlength screws, use them initially, then swap them out before the epoxy sets

[markxengineerin]

I think this is nearly ready at this point

PDF has more details

I am forced to relent on doing the repair with the mast up, because I can't think of a way to drill the necessary holes without spreader removal. Going halfway up mast with no lowers and hacked cap shrouds is over my threshold of dumb. I have found a yard to pull the mast and will show some pics of the actual repair in a week or 2 when it happens.

Thanks to all for the constructive criticism, definitely helped get somewhere I feel much better about in the end.