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Old 30-12-2011, 12:49   #1
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Tying lines together - Strength loss?

OK engineers and technical types...

I have a 200 foot 5/8 Nylon line for a Sea Anchor. I want to have a longer line than that and should probably have more like 400 feet. Since the 5/8 takes a fair amount of space I am thinking of adding 200 feet of a Dyneema 3/8 line with a breaking strength of >15,000 lbs.

I realize Dyneema has no stretch, but the 200 feet of Nylon 3 strand will take care of that.

Two questions.....

1.) what is the best know to secure two lines together so they don't come apart?.... Two bowlines?

2.) What percentage of strength is lost by connecting the two lines. Assume both lines have the same original breaking strength to begin with.
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Old 30-12-2011, 14:02   #2
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Re: Tying lines together - Strength loss?

A sheet bend will work but Dyneema and other super ropes are much more weakened by sharp bends in knots, and slippery so they don't like to hold knots than 3 strand or double braid dacron or nylon. A knot that may work to join the lines is tieing a granny knot with each line around the other line. You tie the granny knots and then slide the knots together. Not a very good description and I couldn't find an illustration on line. Believe it's illustrated in Toss's 'Rigger's Apprentice'.

I'd splice an eye with thimble into the Dyneema. Dyneema is super easy to splice, hardly harder than tieing a knot. Then tie the nylon line onto the Dyneema with a bowline. Except possibly in a tow by a much larger vessel, lines almost always part from chafe, not exceding the strength of a knotted rope.
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Old 30-12-2011, 14:23   #3
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Re: Tying lines together - Strength loss?

You could splice in a thimble to the ends of each and use a shackle between the two, or thimble thru thimble into each other. With Synthetics, knots tend to brake right next to the knot when under lots of stress (no stretch at that point).
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Old 30-12-2011, 14:37   #4
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Re: Tying lines together - Strength loss?

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You could splice in a thimble to the ends of each and use a shackle between the two, or thimble thru thimble into each other. With Synthetics, knots tend to brake right next to the knot when under lots of stress (no stretch at that point).
I believe I have seen manufacturers recommend cow-hitching the spliced lines rather than using thimbles; the cowhitch eliminates chafe by eliminating movement, and the thimbles can shift under a cyclic load. However, in this case I wonder if the high-tech line could cut through the polyester (or rather present a sharp radius), resulting in a lower value? I wonder if this has been tested? Certainly, the high-tech line should be the one with the cow-hitch, for this reason and several others.

Definitely splicing, and I'm not a big splicing fan. However, this is a perfect splicing application.
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Old 30-12-2011, 15:09   #5
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Re: Tying lines together - Strength loss?

Quote:
Originally Posted by roverhi View Post
A sheet bend will work but Dyneema and other super ropes are much more weakened by sharp bends in knots, and slippery so they don't like to hold knots than 3 strand or double braid dacron or nylon. A knot that may work to join the lines is tieing a granny knot with each line around the other line. You tie the granny knots and then slide the knots together. Not a very good description and I couldn't find an illustration on line. Believe it's illustrated in Toss's 'Rigger's Apprentice'.

I'd splice an eye with thimble into the Dyneema. Dyneema is super easy to splice, hardly harder than tieing a knot. Then tie the nylon line onto the Dyneema with a bowline. Except possibly in a tow by a much larger vessel, lines almost always part from chafe, not exceding the strength of a knotted rope.
What roverhi said, but instead of a bowline, use a "figure eight follow-through."

Figure 8 Follow Through | How to tie the Figure 8 Follow Through | Climbing Knots

Keep in mind that any knot weakens the rope, but figure eight does retain about 70% of the original strength and is very secure.
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Old 30-12-2011, 15:51   #6
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Re: Tying lines together - Strength loss?

Personally if I were to tie dyneema to anything I would use a triple fishermans knot.
Its very slippery and many knots will pull through.
However spliced eyes would be the first choice.
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Old 30-12-2011, 17:59   #7
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Re: Tying lines together - Strength loss?

If you are talking about bare 12-plait dyneema, there is absolutely no excuse for even thinking about knotting it. It is extremely slippery and doesn't like small radius bends, so knotting is a non-starter. However, as others have said, eye splicing is dead easy, retains nearly 100% of its strength, and won't slip under load.

A quick review of the manufacturers website info will likely set you straight.

Cheers,

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Old 30-12-2011, 18:10   #8
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Re: Tying lines together - Strength loss?

Thanks all...Sounds like an eye splice is needed. At least on the Dyneema, and then a bowline to the eye with the 3-strand.
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Old 30-12-2011, 18:14   #9
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Quote:
Originally Posted by PamlicoTraveler
Thanks all...Sounds like an eye splice is needed. At least on the Dyneema, and then a bowline to the eye with the 3-strand.
If you aren't going to splice I would consider anchor bend or double fisherman knot for tying two different sized lines together in a towing type situation.

I use the double fisherman all the time. It's the first to go to after the basic 4 (square, figure eight, bowline and clove hitch). Well maybe after the truckers hitch...

Here' a cool link for knots - http://www.animatedknots.com/knotlist.php
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Old 30-12-2011, 18:16   #10
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Re: Tying lines together - Strength loss?

If worried by strength loss, why not use a stronger rope in the first place?

Maybe you can splice eyes over thimbles and then use a big shackle to connect the two lines?

They say splicing does not reduce line strength as much as tying does ...

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Old 30-12-2011, 18:25   #11
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Re: Tying lines together - Strength loss?

Quote:
Originally Posted by PamlicoTraveler View Post
Thanks all...Sounds like an eye splice is needed. At least on the Dyneema, and then a bowline to the eye with the 3-strand.
Again--don't use a bowline. It's not very secure for critical applications. Figure eight to an eye splice on the dyneema is much better.
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Old 30-12-2011, 18:37   #12
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Re: Tying lines together - Strength loss?

Quote:
Originally Posted by PamlicoTraveler View Post
OK engineers and technical types...


2.) What percentage of strength is lost by connecting the two lines. Assume both lines have the same original breaking strength to begin with.
From memory most loose up to 50% of breaking strain, think a fishermans bend looses least. Can't find the destruction test data though.
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Old 30-12-2011, 19:26   #13
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Re: Tying lines together - Strength loss?

Eyesplice the end of the nylon.
Eyesplice the end of the Dynema (or polyester line which is really chafe resistant) making the eye large enough to easily pass the whole bundle of Dynema through the eye.
Pass the Dynema eye through the nylon eye then the bundle through itself.
Pull tight, this forms what looks line a balanced square knot between the two lines.
Strength will be about 100% because there is double the line for each one to take strain up to each splice as long as eacheye splice is good.
According to Brion Toss this type of join has been tested close to 100% and, as such, I have been using this technique to join lines for years now with no failure(s).

It is super easy to join and remove lines this way. I have a basket of 500 ft of line that I pass through the eye (big enough for the basket) to join long anchor lines.
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Old 30-12-2011, 19:51   #14
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Re: Tying lines together - Strength loss?

Rick: I agree--that is the best solution.
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Old 30-12-2011, 20:10   #15
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Re: Tying lines together - Strength loss?

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Rick: I agree--that is the best solution.
+ another 1
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