Cast Thimble Modification for Dyneema

[dfelsent]

I like your thinking. As far as rotation testing you could make one up and intentionally have the lashings to one side and load it up. Then unload and load etc. that might tell you how it will work.
Separate question though. What is wrong with the lashings bunching up ? I don’t see right away how that is other than an esthetic problem.

[Manateeman]

The lashings bunching up . Well you have two sources of friction. The first is the contact area where the lashing meets the surface of the thimble or the deadeye.
The second occurs where the lashings touch each other. You are trying to keep the strain on each leg of the lashing equal. Lashings in a curve thimble push against each other. With a straight crossbar in the thimble, or a dead eye with individual holes, this friction source is eliminated. Dyneema tends to flatten out under load if it’s crossing something. This just increases the friction if the lashings are touching each other. It makes tightening more difficult.
What I really worry about is the constant friction as the rig loads and unloads.
Why not just eliminate it by adding a crossbar.
Mark

[Neil C]

Substitute the lower thimble with a 'D' shackle. The shackle has a cross bar welded to it for the lashing to the thimble above and the shackle pin goes through the chain plate hole

[Benz]

The reason traditional deadeyes have the center hole higher than the other two is that tha offset keeps the deadeye from trying to rotate when being initially tightened. The Colligo deadeyes have the same feature, and it's an important one; one that the crossbar proposed wouldn't address.
A cow hitch in the middle, with legs worked outward, would mean the line was crossing itself several times, making it difficult to "twang" each leg in the tightening process.
Lastly, because time is short today, some boats are having deadeyes machined from Delrin, I don't know with what level of success or longevity.

[Muaddib1116]

Originally Posted by Manateeman

The lashings bunching up . Well you have two sources of friction. The first is the contact area where the lashing meets the surface of the thimble or the deadeye.
The second occurs where the lashings touch each other. You are trying to keep the strain on each leg of the lashing equal. Lashings in a curve thimble push against each other. With a straight crossbar in the thimble, or a dead eye with individual holes, this friction source is eliminated. Dyneema tends to flatten out under load if it’s crossing something. This just increases the friction if the lashings are touching each other. It makes tightening more difficult.
What I really worry about is the constant friction as the rig loads and unloads.
Why not just eliminate it by adding a crossbar.
Mark

I understand, I'm just wondering how big a problem these things are in real use. Wouldn't the lashings balance out over time as the rig loads and unloads? That being said, is there really enough movement in the lashings during use that friction would be a problem?

[Manateeman]

The search for a better dyneema terminal continues.
Maybe some member who is computer skilled could please post two photos for us. We found two thimbles on the Wichard web pages, which we have never seen before and look pretty interesting.
The Wichard part number is 7323 . They are selling the clamp but it’s the thimble which is interesting.
The next mystery thimble is in the instructions page for the line clamps.
Next.
Thimble rotation.
Well we do understand why the holes in wooden deadeyes are located in their traditional positions. We just do not agree a crossbar thimble would cause rotation. The manatees are going to throw the cow hitch over the fence because it looks weaker than splicing the lashing line...or lines, onto the crossbar. They also detest being called sea cows and thus the word cow in any context.

The Wichard MXLEVO soft block. This is definitely an interesting design. Our chainplates are big chunks of aluminum bar. We’ll post some photos but if we are going to go to dyneema, the connection hardware has to be something different from what we would use with traditional wire and turnbuckles. We think the photos will help and will try to get them posted today.
Again, thanks for all the responses.
Mark and his “Don’t call us sea cows” crew.

[Spot]

Originally Posted by Manateeman

Maybe some member who is computer skilled could please post two photos for us.

Here you go Mark!

[Manateeman]

Thank you ! Really appreciate your help !
I hope somebody recognizes this thimble or Wichard will respond because it may solve some of my connection worries. Looks very strong.
With regard to the Wichard MXLEVO soft block...any members experiences or applications, would probably be very appreciated by the old, slow, and completely out of modern sailing members such as myself.
Our chain plates.
Too sunny to photograph but I’ll try later today.
They are 3/4 “x 2” bars . Most of the holes are drilled over 5/8” but under 3/4” so we could do the final drill to 3/4 when ready to rig the boat.
The cap and intermediate on the main mast are drilled cross ship. So are all the chainplates for the mizzenmast . The mainmast lowers are drilled fore and aft.
From the center of the hole to the top of the chainplate it’s 1-1/2” or twice the hole diameter and twice the plate thickness. Pretty routine stuff.
We’d like to get rid of all the stainless wire, and if possible, the stainless toggles and turnbuckles too. A lot of the dyneema terminals are on aluminum. We obviously like aluminum but 316 stainless has its advantages.
We started the thread to find NEW ideas. A lot of “what’s wrong with the current fittings” comments but that’s ok. Manatees are use to being speed bumps.
Sincerely...happy trails to everybody.
Mark and his ...”Please don’t say sea cow” crew.

[Muaddib1116]

It's not simply "what's wrong with existing stuff" for the sake of disliking change. I like your ideas, and I see your points, I'm just wondering if you are potentially going to spend a lot of effort and potentially money to solve a problem that's mostly hypothetical.


If you could shape the holes of your chainplates so they are safe to accept bare dyneema, then those Wichard soft blocks look like an elegant solution. You would still want to weld in your crossbar on the steel part to have a straight surface for the lashings.

[Manateeman]

You provided us with exactly what we were looking for...new ideas. Sincere thanks. Definitely got us thinking.
OK. We have a good size (3/4”) hole in the chainplates but it’s sharp 90 degree edges. I really don’t want to bevel off the edges but I’m not sure doing this would reduce the strength. Maybe it won’t.
We have the mast temporarily held up by 5/8” stainless shackles. Some wire and turnbuckles and a lot of lines.
We could go to 3/4” stainless shackles but a dyneema direct connection to the chainplates (I guess) would be a lot stronger.
Dog Bone?
Just thinking...what about stuffing a piece of 3/4” rod into the chainplate. It could stick out both sides long enough for the dyneema and we could drill and tap the ends for washers so nothing can slip off. We haven’t done the final drilling so we could knurl the rod in the middle and have a snug fit.
Chain plate dog bone?
I’ll post a drawing. Thanks again. Mark

[Manateeman]

Chainplate dog bone.
This is just a piece of 1/2” alu rod but I hole is better than my drawings

[Manateeman]

Money? Take a look at the price for stainless 3/4” turnbuckles and toggles? I could ship my manatee crew to Italy for dinner for less. I look at the stainless toggles and think... am I looking at a scratch or ...a crack. I look inside my Sta-Lok fittings and think the same. We’ve had formers we could not get out. I’m not thrilled about aluminum deadeyes or terminal fittings no matter what coating they have on them. The open weave of dyneema, salt, dirt, aluminum...or someday it becomes aluminum oxide. No, thank you.
316 cast stainless. TIG welder onboard. Aluminum argon tanks... I’m a happy manatee.

[Benz]

Originally Posted by Manateeman

Chainplate dog bone.
This is just a piece of 1/2” alu rod but I hole is better than my drawingsAttachment 258598

That would work just fine, as long as everything was secure and tight enough to not shift when on the loo'ard side
Far better, though, if you can, to round the edges in the chainplate holes to accept a Dyneema strop, and round the top edge a little so it can't cut the rope.
It will be less parts and more elegance.
Might be a few hours with the dremel...

Back to the welded bar on the thimble: the lashing legs bunching when in use is not a problem. It's them bunching and even overriding while you're trying to tune the rig. This is why the machined Alu deadeyes are really great. They keep the legs not only separate, but far enough apart to individually pluck each leg as you tighten. It's really hard to do otherwise.
The first loop or leg off the bar would be the tightest to begin with, so the thimble would yearn in that direction, causing all other legs to pile against it until they all had even tension. You would be very annoyed.
If you have a Delrin deadeye machined, and attach it directly to the chainplate with a Dyneema loop, you'll have achieved the pinnacle of elegance.
That Wichard thimble is for a furler torsion cable--I don't see an easy way to adapt it to your purpose. Also, being Wichard, it's probably far more expensive than an aluminum deadeye.

[Muaddib1116]

Originally Posted by Manateeman

Chainplate dog bone.
This is just a piece of 1/2” alu rod but I hole is better than my drawingsAttachment 258598

Nice, this is what I was trying to describe in an earlier post. I think as long as tension is kept, this would work well. The washer idea would help. That being said, that chainplate looks beefy, and it looks like you have plenty of wall thickness on top of the hole (looks like more than the sides of the hole, which would be taking the load), so I think rounding the top edges of the hole so a dyneema line could wrap through smoothly would not weaken anything.

[smj]

I believe they recommend a turnbuckle between the chainplate and dyneema stays if your boat is over 40’ and the rig non rotating.