Cast Thimble Modification for Dyneema

[Manateeman]

Thank you all contributors.
1. Are turnbuckles necessary over 40 feet vessel? We know who has stated this but a lot depends on the vessel and how hard it’s sailed. We have seen rigging so tight you question if the mast can take it. Seen a few masts bent by over pumping the back stay. It might take more time to tune the rig. Where is the data. We are not a performance boat. Manatee move so slowly you can’t tell which direction they are moving.
2. Chamfering. We have a lot of material so I agree, this is not going to weaken the chainplate significantly. The plates are 3/4 x 2 and there is 1-1/2” of material from the center of the hole to the top of the plate.
I like the idea of dumping the jaw/ jaw thimbles which are not cheap. Again, it’s the scratch or crack inspection issue. Even if we need to stay with turnbuckles.
3. Delrin deadeyes. I remember there was a post on plastics as an alternative to aluminum. Lots of plastics to choose from so I need to do more research on this.
I like this idea as well as going directly to the chainplate.
4. Dog bone shaft into chainplate. We could try this easily. The chainplates are not drilled to 3/4” yet so we can get a nice tight fit by knurling the bar just where it fits into the plate. Adding washers to the ends is easy. You can make them any length. So here is my first question. If we go 7/16 dyneema to a dead eye or some other thimble... do we use this bar on the chainplate for the lashings or do we use a pre made loop or some Wichard soft shackle. There are a lot of combinations using fitting we’ve never seen before.
What interests me about the dog bone chainplate is the large diameter (3/4”) and the nice smooth surface we could get with stainless.
Poking the dyneema right through the chamfered chainplate will work but it’s a harder bend than loops over the dog bone.
Comments? Ideas? Thanks in advance for all replies.
Mark and his ever hungry crew.

[Muaddib1116]

Why would the bend be tighter through the chainplate holes than the dogbone? They are both 3/4" right? So if you round the chainplate holes, then it will be the same radius as your dogbone. Obviously, that's a more permanent action to take. As far as the dogbone, I am trying to imagine if there is a reason not to put the lashings around the dogbone itself, and nothing has come to mind yet.

[smj]

Colligo recommends turnbuckles on boats over 30’ as it’s hard to get the needed pretension with just lashings. A badly adjusted or loose rig will not only affect sailing performance it can also lead to rigging failures.
Our catamaran is 39’ and we have a rotating rig so not nearly as much tension needed. Since we had new turnbuckles we decided to keep them as it makes the rig much easier to tension, and I’m glad we did. We set the tension on the rig once using the lashings then re tensioned twice with the turnbuckles.
We have a Colligo fitting on the turnbuckles and the lashings go from this fitting to a SS thimble. In the 2.5 years we’ve had this rig we’ve had no problems with the lashings trying to override each other on the thimble, and this is with loose tension. Also no trouble with chafe. Our upper thimble attaches to an appropriately sized toggle, and no signs of point loading there.

[smj]

Pretty cool video of Billy and Sierra of Tulsa Endless Summer tensioning their lashings.

https://youtu.be/JfVbzKPlI7k

[Manateeman]

We agree. The dog bone is simple and you are correct. No reason it cannot take the place of a lower dead eye. Chamfering the chainplates is rather permanent and would involve removing a good amount of material to get a smooth radius.
Dog ones with washer ends would be a lot easier.
I need to finish some projects before I make one but I’ll post ASAP.
Thanks again. Mark

[fxykty]

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

Do remember that the leeward shrouds will be relatively loose when the rig is loaded and when pumping through waves. Whatever connection you decide on make sure it can’t come apart when there’s no tension. The pictured system will fall off the bar.

[Manateeman]

The pictured system IS NOT the system I intend to use.
I specifically stated IF we used a dog bone it would have washers at the end of the rod going through the chainplate.
Honestly. I sometimes wonder if it’s worth posting at all.
I sincerely thank those who have submitted thoughtful and constructive comments .
I’m sorry but we’re done with this thread.

[Pauls]

Manateeman, I like your idea of a crossbar welded into stainless thimbles, especially with the addition of a roller. A major reason why lashings are not recommended on larger boats is the friction required to pull the lashings thru the dead eye holes. I like the idea of lashings running over rollers. The rollers can be grooved to keep the lashings located on center. They could greatly reduce friction which would simplify tensioning the rig and would enable the use of lashings on larger boats.

I'm going to build up a few. Thanks for the ideas.

[Manateeman]

We are not sure you would even need to have rollers on the crossbar. If the crossbar diameter equals the width of the thimble, you have a nice reduction in friction.

[Pauls]

Agreed that a larger bar will help. And dyneema is pretty slippery. But it seems to me that a roller will still reduce friction, and it is so easy to do, why not?

One challenge with a roller is that the roller will be heavily loaded and stainless is a lousy bearing material. A moly filled grease might be all that's needed. I'm familiar with teflon filled electroless nickel plating which is very slick and durable, and would be a good match with the stainless galvanically.

I think I'll build a couple test parts and see how they do. An improvement on the dead eyes, both in cost and especially in friction reduction for larger boats is very attractive.

[Manateeman]

Thank you for your post. It’s exactly what we were hoping for...new ideas !
Please post your designs. Again, thanks from the entire crew.
Mark and the manatee gang...proud inventors of the pizza bazooka.

[Muaddib1116]

A seamless roller will need to be in place before the crossbar is welded, and it may not survive the heat. A split roller that is popped on afterwards, will have the split, which may cause friction, or spread apart under load and cause problems.

[Manateeman]

If you make the roller out of stainless and the crossbar out of stainless and you TIG the crossbar to the thimble..exactly where is the heat issue.
Anyway...we just put that idea out there as someplace to start the thinking about new ideas...probably the crossbar will not need a roller anyway.
There are a lot of plastics which are heat resistant and we have seen a number of TIG tricks when welding with which to localize the heat.

[glenn.225]

I like this idea but I do see an issue here, in that the lashings do not all have equal amounts of "travel" over the "bearing". So you will still get the friction of the lashings passing one another and one having more travel than the next. If the "bearing" was made in multiple sections like the sheaves of a multi-part block then yes, I think it would be great. But with just one bearing I don't see much advantage.
Thoughts?