Dynema to dacron splice? - SailNet Community
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post #1 of 10 Old 04-03-2017 Thread Starter
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Dynema to dacron splice?

Does anyone know the whereabouts of directions for a good way to splice dacron double braid (sta-set) to 12-strand high modulus (dyneema)? Replacing my SS running backstays.
Thanks for any leads.
JV
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Re: Dynema to dacron splice?

Not really. There is a splice for it, but it has a bad habit of herniating.

A better option is to buy an all dyneema line, then add a cover on the working portion.
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Re: Dynema to dacron splice?

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Originally Posted by svselkie02 View Post
Does anyone know the whereabouts of directions for a good way to splice dacron double braid (sta-set) to 12-strand high modulus (dyneema)? Replacing my SS running backstays.
Thanks for any leads.
JV
there is couple of ways to do it and many you tube videos
You can also buy dyneema double braid and strip a section of the cover videos on that too
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Re: Dynema to dacron splice?

Thanks, Stumble & Overbored. Two good possibilities to choose from. The splice in the Youtube video looks like it would work--its basically an elegant-looking brummel, similar to an eye splice in dyneema. Stumble, I assume you know what I'm doing--running the runners around a block to the lazy primary winch.--an idea Brion T. suggested in his board. Wouldn't the HM line travel inside the cover in that application?
JV
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Re: Dynema to dacron splice?

The problem with the splice that Overboard linked to is that if you don get it exactly perfectly balanced between transferring the load between the core and the cover, and I have no idea how to get this to actually work out correctly, when placed under a high load the splice herniates and either the core or the cover takes to much load and gets distorted. It works fine for low load applications like a furling line, or lazy jack lines, but for a backstay I doubt it. I have ruptured a couple of these splices before giving up on them.

For a backstay you really want the dyneema to carry the load all the time to keep the stretch down. You don't gain anything by transferring the load to a polyester line instead.

My recommendation would be to buy enough dyneema to run from the mast all the way to the winch plus about 10 feet. Then buy another ~20' of Yale Cordage Line Cover Only | APS .

Then just bury the dyneema inside the cover, and do a standard taper splice such that you have ~10' of just cover hanging off the back.
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Re: Dynema to dacron splice?

it does depend how much load the tail will see if the backstay goes direct to a winch then the splice will have a lot of load, if the line goes through, say 8 to 1 blocks and the tail is just there to cleat the line and for your hand grip there is not that much load on the splice.
In the case of running backs where the working end is short adding a cover to the line is a good way to go.
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Re: Dynema to dacron splice?

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Then just bury the dyneema inside the cover, and do a standard taper splice such that you have ~10' of just cover hanging off the back.
Stumble, this sounds like the route to take but I'm not getting that last part. I'm picturing the bottom 20' of dyneema covered, including a core & cover tail of about 10' past the winch.
But then where is the 10' of empty cover coming from?
What keeps the strain on the dyneema and not on the cover where the winch grips it? If you connect the top of the cover to the dyneema with the tapered bury inside the dyneema, then doesn't the cover end up taking all the strain from that point down, as the dyneema just slips freely inside it? Or is the tapered bury at the bottom end, and if so, how to you anchor the top of the cover to the dyneema core so the winch doesn't slide it down? Or does the cover grip the dyneema adequately along its entire length?
Pardon my density here.
Thanks.
JV
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Re: Dynema to dacron splice?

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In the case of running backs where the working end is short adding a cover to the line is a good way to go.
Thanks, Overbored--the splice still looks like a good one to have in the 'repertoire'.
JV
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Re: Dynema to dacron splice?

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Originally Posted by svselkie02 View Post
Stumble, this sounds like the route to take but I'm not getting that last part. I'm picturing the bottom 20' of dyneema covered, including a core & cover tail of about 10' past the winch.
But then where is the 10' of empty cover coming from?
What keeps the strain on the dyneema and not on the cover where the winch grips it? A very small amount of load will be on the core, not much though. Basically the dyneema and the core get loaded a little, the core stretched but the dyneema doesn't (or far less). So more and more of the tension gets applied to the dyneema because it doesn't stretch. It's functionally the same as attaching a rubber band and a piece of twine the same length to something then pulling. Technically the rubber band will stretch minutely, but all the load is carried by the twine.

If you connect the top of the cover to the dyneema with the tapered bury inside the dyneema, then doesn't the cover end up taking all the strain from that point down, as the dyneema just slips freely inside it? No, the two lines act independently as to load carrying, the taper splice just prevents them from slipping past each other.

Or is the tapered bury at the bottom end, and if so, how to you anchor the top of the cover to the dyneema core so the winch doesn't slide it down? Or does the cover grip the dyneema adequately along its entire length? Too many pronouns I can't follow sorry. Basically starting from the top of the mast... The dyneema is attached runs down the rig to the block, close to the winch there is a taper splice where the cover starts. Then the core and cover run back together for some distance, where the core just ends but the cover keeps going. At the end of the cover, do use a reefing splice, or back splice to finish the end cleanly, you could just burn it, but meh.
Pardon my density here.
Thanks.
JV
Sorry, I have been messing with tapered lines so long it's just second nature to short hand stuff.

Let's say the distance from the mast thru the deck hardware to the base of the winch (at maximum load) is 50' exactly. You want the cover to be over the dyneema past this point by at least 2' to make sure you really are at max load, and for a bit of a margin. So the first 46' is uncovered, the next 2' is the taper, the next 10' are covered, and the last 8' is just the empty cover.

What this does is gives you a big working section that is fully covered so the only thing that hits the winch is covered, and you get a long tail to make coiling easy when you are putting it away. If you decide the tail is too long, just cut off a piece, its cheap stuff so no worries.

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Re: Dynema to dacron splice?

Got it--so even though the cover provides the grip at the winch, the dyneema is gripped within the cover and is not just sliding freely inside the cover. IOW, it's not as though only the rubber band in your analogy is gripping the winch while the twine is allowed to slip.
Thank you for taking the time. That will be the plan.
JV
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