Troubleshooting a rounding-up problem

[Be Free]

You shrouds should be "snug" without pressure from the sails. When you are sailing the windward shroud will be "tight" and the leeward shroud will be "looser".

Each hole on the verier adjuster will change the stay length 1/8".

[DaveC426913]

Yeah, I think I. may have found the problem...

[Be Free]

[DaveC426913]

Welp. I started to replace my vernier adjusters with turnbuckles. Ran into a problem immediately.

The aft shroud is several inches more shy than the fore shroud. (I mean the gap from the tang to the swage.) The fore shroud has about 8", while the aft shroud has about 10".

Clueless, I had only measured the fore shroud for fit. My new turnbuckles were too short for the aft shrouds, and I only realized it AFTER I had cut the vernier adjuster off the shroud swage.

I had just killed my boat with no way forward or back. I had to make up that 2" or I couldn't even re-attach the shroud and go home, let alone sail.

I had to cut** my vernier adjuster into a section only four holes long to make up the difference. All that work to get new turnbuckles and I've STILL got vernier adjusters!

I only did one side. No point in doing the other side until I find a proper solution.

So we went out for a test sail. And the danged turnbuckle popped right out. Almost dismasted us. Luckily the other turnbuckle held until I could douse the sails and putter back to shore.

As far as I can tell, it sheared its threads. Look at the one on the left, its threads are sharp. Te one on the right is the one that failed. Its threads are sheared off.





I'm going to take the turnbuckle back to the shop and ask them about it. But before I blame the hardware, I have to consider if it's possible that I failed to put enough thread on.

This gives me concern, in that it means I have a much smaller zone of adjustment between too much and too little. It's down to less than an inch.


** that cut was a trip to the hospital and a four hour stay for five stitches. Damn near cut my hand off with my angle grinder. (I have pics! ) Didn't stop me going out sailing when I got back tho ... Been a long day.

[LordElsinore]

oh man, thanks for sharing. Been watching the thread to see how your project turns out

[Dougiestyle]

Oh Yeah Verrrry Interesting. All good Info

[DaveC426913]

Wisdom coming in from the engineers on my physics forum:

"I have been told that full strength is obtained with seven turns. But with fine threads, I prefer to use one outer diameter, the length of a nut."
(I was def within that)

"The threads on the rods were probably rolled, not cut, and so will be rounded and under-size at the ends.
(My next question was going to be: should the bolt be loose in its socket?
There's definitely a little play in it. I can wiggle it around a tiny bit, at almost any length.

My naive thought when I observed this was 'Hey, doesn't that mean the threads are not fully overlapped? Isn't that weak?' But who was I to argue with marine-grade hardware?)

"You might need to cut off the rolled end with a cutting disc to get a constant full thread OD. That will allow closer contact between the screw ends, with good thread when short. If poor LH and RH threads at the ends meet, they will reduce the range of adjustment."

(The screws don't touch in the middle. There's a hole for a lever and for a locking wire.)


I'm not sure how much I could cut off, but that doesn't solve my problem, does it? I don't have the option of screwing the turnbbuckle in more than it is now. All I would be doing is cutting off useless thread.

"Lateral vibration of a tight stay in the wind will produce very high axial forces on the turnbuckle, due to the triangle of forces being long and thin.
This is also a special case since each lock-nut is working with the rope tension to strip the thread."
(I think this is exactly what happened.)

"If you adjust the turnbuckles under load, without lubrication or an anti-seize compound, the stainless steel threads will probably gall. That may remove some of the thread OD material, just where it is most needed. That could generate the damage you show."
(I adjusted them at-dock and only hand-tight. Nowhere near as tight as the shrouds are recommended to be.

In fact, one of my theories was whether not having the rigging tight enough could have caused enough wobble to wear the hardware.)


My take-away here is that - despite being sold in a marine chandlery, where they tend not to cheap out on hardware - these are cheap turnbuckles, and failed for that reason.

I will do further research and see what the chandlery has to say.

[DaveC426913]

Interesting. That turnbuckle I posted a pic of is selling for $75.

The ones I bought are $14.

In fact, my 20/20 hindsight is reminding me that the reason I didn't do this upgrade years ago is because I was looking at $75 turnbuckles last time - and this time my critical judgement failed me and I bought impulsively.

This site has the exact size and type, and calls them "Economy". "600lb working load"
https://ca.binnacle.com/Turnbuckles-&-A ... _info.html

[DaveC426913]

Back from the chandlery.

Look at the difference in thread length (and thus range) and in thread fineness (and thus strength):


And the premium turnbuckle only needs 1/4" of thread engagement because it's so strong.

I think my engineer buddies were spot-on when they suggested the "Economy" one was rolled steel rather than cut, and therefore the threads are poorly-formed and shallower. They can just pull right through under load.

"Oh what mangled fruits we reap
When we first try to buy cheap!"
(I just made that up.)

And the fruits I reaped were five stitches in my arm and almost having my SeaSaw dismasted.

[NiceAft]

You did not mention the thickness of the screws. Unless I’m imagining things, the expensive one looks to be significantly thicker. I have to believe that increases holding power. I’m not an engineer, but that is my thought. I’m ready to be lambasted by those who know better.

[DaveC426913]

You did not mention the thickness of the screws. Unless I’m imagining things, the expensive one looks to be significantly thicker. I have to believe that increases holding power. I’m not an engineer, but that is my thought. I’m ready to be lambasted by those who know better.

They should be the same thickness. They're both 1/4".

[UPDATE:] A closeup side-by-side:



What my engineer buddies are telling me (in great technical detail) is that, even with the same shank thickness, the threads will stand more proud on higher quality hardware, making for more thread-to-thread contact.

I can transcribe the relevant correspondence if you're interested. Or you can just read it here:

https://www.physicsforums.com/threads/h ... st-7122862

Scan for Baluncore's posts in particular, though there's plenty of technical nutritious goodness throughout thread.

[NiceAft]

A picture is truly worth a thousand words. Amazing difference in those threads.

[Be Free]

The quality turnbuckles are open body as well. That will allow them to drain any salt water that splashes on them and gives you more opportunity to catch problems before they become critical.

Opinions vary, but I never use closed body turnbuckles on my rigging.

[DaveC426913]

Cost: $400, 5 stitches

[DaveC426913]

Epilogue: I do not know if it cause-and-effect but I took her out for a spin afterward.

In a light 4 knot wind, doing about 3.5 knots, I completed three consecutive tacks of 100 degrees. That's 10 degress less than my previous bests and about 20 degrees less than my usual worsts.

I still rounded up once, though I had the main sheeted all the way in, and I didn't ease it as I started rounding up.

I have yet to test her in some stronger breezes.