interesting failure- dyneema rig terminal

[markxengineerin]

I discovered this a couple days ago, sailing off the coast of NJ. It happened sometime between Maine and here. This was the first sailing after a refit which included the synthetic rig. I am working on a detailed analysis and fix strategy, but wanted to get input from others here before I spoil the group creativity by sharing. Thanks!

[neilpride]

Horrible job,i don't know who did that, but please, tell me that the bolt in the picture cross the whole mast to the other tang.. no? and i see a small alu bracket attached to the spreader?
No compresion tube linking the stb port tang?

Expensive repair, sorry to sound negative, but buckling in the spreader area compromise the whole thing.

[markxengineerin]

Yes, it's a through bolt. The small aluminum bracket is not structural- it was taped there to keep the dyneema shroud roughly in place in the event of a failure like this one. Serves the same purpose as the tiny screw in Colligo's design:

Their design is a lot better against this type of failure than mine was. Bolt length is kept as short as possible w/ counterbore, bolt hole is offset in the part to increase moment arm of the support column. My design was easy to make with manual machine tools, and I did not see this failure coming at the time. Hindsight 20-20

There is a compression tube, but I haven't disassembled yet to see what size it is.

It's not going to be a fun repair, but shouldn't cost anything besides my time and some steel/aluminum stock + hardware.

[neilpride]

To much lever arm? both lowers should be as close posible to the mast wall , i see in the pic from colligo how both lines run to just a single cheeky tang?

[markxengineerin]

Yes-better design for sure. I was going for commonality of parts. 6 pieces total, 2 for the uppers and 2 stacked each side for lowers. The stacking was a bad idea.

[kenbo]

I'm not a structural engineer but the lever moment is magnified tremendously as a result of your stacking design.

I would try to design something comparable to the tangs as initially installed.

I also don't share your thoughts on this being an easy repair. the mast's integrity is seriously compromised in a stressed area.

Are you currently in NJ?

[neilpride]

Yeah well i see the PDF , to long , yes, you should use a single cheeky tang to acomodate both lowers, bolt should be tight, tolerance should be close fit, compresion sleeve should be double in diameter with you configuration , not good, and fix that with the mast in place its a pain in the ass, probably built a external sleeve around the area , you should fix that bend in the mast, i mean , its unrealistic do a proper fix with the mast up..

[markxengineerin]

Yes currently in Atlantic Beach. I didn't mean to say easy, just not terribly expensive if I can avoid pulling the mast, welding, etc. I used up the budget for this type of stuff already, going to have to get creative and plan something inexpensive yet also safe.

[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.

[markxengineerin]

Ah, you're right, for some reason I always thought A.B. was new jersey. Thanks for the tip on the yard, I may end up there but will see what I can do alone first.

[jfranta]

There is almost always a business case to buy what exists already then to make it yourself. 1000's of Real Cheeky Tangs from Colligo Marine out there with 0 failures on them.

[wholybee]

I had a somewhat similar failure of a traditional rig. The rigger (done by a previous owner) failed to install a compression sleave, and the bolt damaged the mast, elongating the hole.

After consultation with a couple riggers the fix that was chosen was to convert from a through mast bolt with tangs, to shroud terminals. The terminals required a larger hole to install, thus removing all of the affected mast material.

The other proposed fix was to make a partial mast sleave over that section, gluing the two halves of the sleave together to the mast with an aircraft adhesive. Such a repair might be what you need, in addition to whatever fix for the cheek block and too long a bolt.

[MicHughV]

I am a structural engineer.

First thing that comes to mind, as others have pointed out, is the long distance from the mast. ie, a very long lever arm carrying an extremely high load.
Second thing is those big black padeyes, for want of a better word. Their large size means that the actual padeye can also induce an enormous load on the mast, which they did. The long lever arm being the cause, as one can figure out the horizontal and vertical components of the shroud load.

A way to address this problem maybe is to have a basic long stainless steel shroud tang, fitted adjacent to the mast, as one would see for a regular wire setup. The lower part of the tang would angle out from the mast a bit.
If those black padeyes could be squared off, you could then fit one each side to the lower end of the tang, connected by a pin.
Should solve your problem.
Post # 4 kinda shows what I'm talking about, except have the tang bent out to line up with the shrouds.

[chris95040]

So that 'engineer' in your username, Lemme guess, civil? 🤣 (jk jk i have made plenty of mistakes myself)


Seems now you have two problems to solve- the original shroud problem needs to be addressed with far less lever arm, and the new buckle in the mast needs to be addressed.

How much does it really cost to have the rig dropped onto some sawhorses? A buckled slender column is a serious problem. Like standing on beer cans with vs. without dents.

My mast has some serious tangs with mast attachments that include 2 bolts and internal compression tubes, vertically spaced far enough to (probably) span that whole buckle. Perhaps something like that would do the trick.

[ABJ87]

Did you make calculations on this design?

With all due respect I think it’s a poor choice to assume the bolt stays tight enough to allow the cheeky tangs and sleeve to be treated as a solid feature and have the moments resolved internally.

Due to where the bolt yielded, buckling and cracking of the hole, I suspect the sleeve (if any) is much smaller than your sketches indicate.

To make this design work the bolt, sleeve and cheeky tangs would would need to be significantly larger counter the increase in moment arm. The original tang was probably only cantilevered maybe .125-.25 from the mast vs 1-2inches from this design? 8X increase!

I think MicHughV is on the right track for the repair. Abandoning what you have now for a much lower stressed traditional tang.