Which knot is best for synthetic line?

[Hermit Scott]

The parts are $350 to replace my split backstay. I won't have the money for that until The end of may. I have a synthetic 1/4" winch line I want to use as a backstay until then.
It is 100' long. I am going to use a cowhitch at the top so I will have two lines coming down. There is a pin at the point where the split in the backstay meets. I am going to tie to that pin.
So I have two ropes that will terminate at the pin. What is the knot I should use for this line. This synthetic line is kind of slippery. I have been using it as a halyard but it sucks for that mission because it slips on the winch.
Can I tie two lines into a buntline hitch that has two lines following the same path, or should I use a fishing line knot because of the slipperyness of the line? But will the fishing knot work with two lines in it?
Obviously Saildog and Ross have the answers if you've been following the other knot thread! I'd like to see Ross and Saildog face off in a knot tying contest.

 

[Ross]

Knots are all about friction. How big is this "pin" diameter and width? You could carefully run a double line in a buntline hitch being very carful to keep the hitch fair and to draw it up evenly. How do you intend to tension the backstay after you get this part rigged? If you leave the tails long enough you could bring them alongside the standing part and sew them down with palm and needle.

 

[sailingdog]

Do you know what the synthetic line is made of??? Also, how tolerant of UV is the new line? How chafe resistant is it? Is it a double braid or a single—double braids are often far better for such a use since the outer braid, especially in dyneema or spectra-cored lines is mostly for chafe and UV protection, with the majority of the strength in the core itself.

You could tie the two lines in a single buntline hitch. Most likely once the backstay gets loaded you'll have to cut that knot...

However, my real worry is that you're using a cow hitch at the top, which means that if either side breaks, the top may come undone, since a cow hitch isn't really secure unless both sides of the line are loaded...otherwise it can slip quite a bit. I would personally recommend that you cut the line, tie two separate knots at the top and tie two separate knots at the bottom. This would give you a bit of redundancy. However, it would more likely than not put most of the load on a single line, since I seriously doubt you'd get both lines tied off perfectly evenly. So the strength of the line is a serious concern.

 

[Ross]

I am concerned that you simply don't have room at the terminal points to get this "right". The sheeve diameter for line should be your guide for the pin diameter for the terminal points. I think that were it mine I would make shift with galavnized 7x19 wire rope and saddle clamps until I could afford to do it neat.

 

[sailingdog]

Ross— I believe he's talking about the backstay, not the topping lift. There's no sheave for the backstay.

I think making up a temporary backstay with line is a bit foolish overall, since in almost the same amount of time, he could easily make up a replacement upper backstay with 1x19 stainless wire and two Hayn HiMod or StaLok fittings.

I am concerned that you simply don't have room at the terminal points to get this "right". The sheeve diameter for line should be your guide for the pin diameter for the terminal points. I think that were it mine I would make shift with galavnized 7x19 wire rope and saddle clamps until I could afford to do it neat.

A Hayn HiMod eye for 5/32" wire is $28.16, 40' of 5/32" 1x19 316SS wire is $32.40. Total cost is less than $100.

 

[Hermit Scott]

I think the line is Amsteel. It's UV resistant and has great chafe resistance. I bought it from a winch store, but I think it is the same thing they use for marine use.
The pins are 1/2" by about 1/2" width. I am going to put a thimble in to increase the diameter.
The reason I wanted to use a cowhitch is because I will not be able to get both legs of this the exact same length. It looks like the cow hitch will be self leveling under a heavy load especially with amsteel.
How I will tighten it is; I have an adjustable split backstay. It has some blocks with purchase and a cam cleat. I am going to hook it back up to the chain plates with bow shackles so I can run more amsteel beside those, just in case that part of the backstay is old. It looks to be newer but who knows. The part that failed was an old closed style turnbuckle. The wire didn't fail, the toggle stud failed inside the turnbuckle.
I bought the thickest polyester thread I could buy and some doll needles. I have been using this to whip lines and repair my crappy main sail.
I will use the doubled buntline and whip it alongside the standing part. Thanks for the quick response since I am leaving within the hour to do this.

 

[Hermit Scott]

Ross— I believe he's talking about the backstay, not the topping lift. There's no sheave for the backstay.

I think making up a temporary backstay with line is a bit foolish overall, since in almost the same amount of time, he could easily make up a replacement upper backstay with 1x19 stainless wire and two Hayn HiMod or StaLok fittings.



A Hayn HiMod eye for 5/32" wire is $28.16, 40' of 5/32" 1x19 316SS wire is $32.40. Total cost is less than $100.

This is a temporary fix. I would love to replace the backstay with SS however the parts are $400 and I won't have the money until the end of May when my shipment of machines arrive from Taiwan.
I really like HiMod fittings. I like the crown ring that keeps all the seperate wires in position while it's being tightened.
The backstay is 1/4" and the split part is 5/32" I think. That's 2 5/32 eye terminals, 2 5/32 forks, one 1/4" eye at the top, a turnbuckle and a 1/4" stud terminal above the turnbuckle.

 

[Ross]

Hermit, You can get all the polyester thread you need from a yard of sta set double braid. just pull indivdual yarns as you need them and pull them across some beeswax.

 

[tommays]

The issue with line as standing rigging is the bend radius and it requires a solid thimble as the standard rope ones will bend under the load

If go below the bend radius you lose

 

[RichH]

Hermit -

The ONLY 'safe' connection for AMSTEEL is a 'locked' Brummell Eye Splice. Amsteel does not hold 'knots'; it's just too 'slippery' to hold any 'knot'. Any good rigger should be able to give you a Brummell eye splice (accept no alternatives).

http://www.neropes.com/SPL_12Strand_EyeSpliceBrummel.aspx

 

[sailingdog]

Hopefully, the line is not amsteel. I believe RichH is correct about Amsteel and how slippery it is... as many of the other high-tech materials are almost as bad. There are some knots that will hold in Amsteel, other than a locked brummel splice, but they're more used in fishing than in sailing, as they were developed for the UHMW synthetic lines like Berkeley Fireline.

 

[Ross]

I am not familiar with the latest high tech lines. I do understand that some of them rival steel for strength size for size. Has knot development fallen behind rope development to the extent that we are in need of a solution to a problem equivalent to sewing jello?

 

[sailingdog]

Yes, and do you have a solution for sewing jello handy??

I am not familiar with the latest high tech lines. I do understand that some of them rival steel for strength size for size. Has knot development fallen behind rope development to the extent that we are in need of a solution to a problem equivalent to sewing jello?

 

[Joe]

Amsteel (single braid Dyneema) comments.

As Rich said... don't waste time trying to knot it... an eyesplice is the way to go.. either a compact one with a thimble or a long splice that you can "luggage tag" to a shackle. The common way to use this high tech line in a halyard application is to cover the handled and cleated section with a more comfortable polyester jacket. You could take a less expensive double braid such as Samson LS and simply use the existing core to fish the new dyneema core into it, then bury the cover into the core with a taper splice and lock stitch it up. Or... you can purchase special "cover only" products that come with a messenger line inside it to pull the new core through.

Both my jib halyards are constructed this way having replaced the old wire/rope units.
I initially used this solution because the limited clearance of the masthead sheaves restricted line diameter to 1/4 inch on my Catalina 27.

(I deleted the strength table because it was jumbled (I'm not that high teck) but the tensile strength for 1/4 amsteel is 8,600 lbs. Here's the link: http://www.apsltd.com/c-1486-single-braids-dyneema-vectran.aspx)

AmSteel Blue - Samson

Construction: 100% Dyneema SK-75

AmSteel Blue is a 12-Strand braided rope utilizing Parallay design with Samson's proprietary blue Samthane coating with Dyneema® SK-75 fiber. This rope yields the maximum in strength-to-weight ratio and is stronger than wire rope constructions - yet it floats. Superior flex, fatigue and wear resistance. For better handling and cleating we can cover all or part of the AmSteel with a polyester jacket.

Common Applications
Uncoveredrimaries in cascades, vangs, traveler bridles, trapezes on dinghies. Great as a wire replacement.
Covered: Lightweight sheets for big boats, all halyards, tack lines.

Hermit could rig his temporary backstay by doubling the amsteel through a block at the masthead. Run the lines through the split backstay gizmo, splice in a long eye at each end and shackle them to the tangs. NO KNOTS this way and the hardware and line are reusable.

Johnson Split Backstay Adjuster Cars

 

[Hermit Scott]

Hopefully, the line is not amsteel. I believe RichH is correct about Amsteel and how slippery it is... as many of the other high-tech materials are almost as bad. There are some knots that will hold in Amsteel, other than a locked brummel splice, but they're more used in fishing than in sailing, as they were developed for the UHMW synthetic lines like Berkeley Fireline.

UHMW is what the line is, with a UV coating. It is really a winch line. I was using it as a halyard for a while. I tied it to the bow with a bowline and cranked the crap out of it on a winch to be able to put my forestay on(I didn't release my topping lift and mainsheet tension, oops). I tied another bowline for the halyard and it wouldn't come undone. The bowline was impossible to untie. I cut it off. There is an eye splice in one end with a galvanized thimble. I don't want to use it because I could only run one line, and I have to tie a knot on the other end anyway. The cowhitch isn't a knot that can come undone so that still leaves me with only one knot.
This is temporay, but it must hold like it's permanent. If I were comfortable tying fishing knots I would use one, but I'm not. I will tie a buntline with a bunch of half hitches above it. If I make it neat enough to the untrained eye, it may look like I knew what I was doing. Also I am going to whip the working part to the standing part.

 

[RichH]

Hermit -

If you want the best secure knots for 'slippery' rope (such as the modern kernmantles used for mountaineering) then suggest you consider the 'terminal' knot to be at least a *double figure of eight* tied to a doubled 'alpine butterfly' (tied 'gun tackle' fashion to the fig.8.

http://www.abc-of-rockclimbing.com/climbing-knots/doublefigure-eight-loop.asp
see 'doubled knots'. This way will give you the max. friction on a VERY slippery rope material. A buntline, etc. is probably *just not going to work* ..... and may lead to 'catastrophe'

The caution remains that Amsteel UHMWPE is one of the 'most slippery-est' rope materials there is. As per the mfgrs. recommendations, You 'should' splice eyes in the ends as previously listed.

Better to be safe than sorry.