quick rigging jib sheets

Moderator: GreenLake

Postby TIM WEBB » Wed May 02, 2012 11:18 pm

If you bartack, or even handtack, the fingertrap, then you need very little running end captured inside ...
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Postby K.C. Walker » Thu May 03, 2012 11:44 am

Tim,

I totally agree about likin’ this thread! It's turned out to be even more interesting and informative that I expected. I guess it should not be any surprise that a parachute guy would come up with a cool variation of the soft shackle.
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Postby K.C. Walker » Thu May 03, 2012 12:01 pm

GreenLake,

I made up a couple of those soft shackles with the self tightening loop last night. That's a very slick and easy to do shackle. Thanks! It's fun but I do still have to follow instructions for making the diamond knot.

As with many things that I just find out about, I end up googling obsessively... It turns out that Annapolis Performance Sailing now only makes and sells that style of soft shackle. They've put up a little YouTube video about the superiority of this style.

I'm going to be making up some halyards. Now that I'm on this soft shackle road, I'll be applying it to that, as well.
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Postby TIM WEBB » Thu May 03, 2012 1:50 pm

I wish I could take credit for inventing the SLINK, but I'm afraid I can't ... :P
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Postby jdoorly » Fri May 04, 2012 10:48 pm

Hi Tim, thanks for the explanation but the meaning of bartack, handtack, and fingertrap eludes me?
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Postby TIM WEBB » Sat May 05, 2012 12:01 am

A bartack is a very tight, compact stitch pattern made by a specialized sewing machine that is dedicated to that stitch. The machine has a cam on it (like a "program") that tells it how many stitches to make. 24 and 42 are the most common. It first does a couple of passes of straight stitch, then a zig-zag pattern. The length and width of the stitch is adjustable, to an extent. Unlike a normal sewing machine, once you mash the go pedal, there ain't no stopping it! :shock:

It's used for adding reinforcement to very small areas, and also for securing fingertraps in lines, like in the pic I posted of the SLINK being used to attach lines to a riser ...

A fingertrap is simply a use of the old "Chinese fingertrap toy", where you stick your fingers in each end, and if you pull in opposite directions, the weave of the material draws closed, and you can't get it loose until you push your fingers together again. With a "hollow braid" line like Spectra, you can draw a bitter end into the line, and given a sufficient length "trapped" into that line, the more you pull on it, the tighter it holds. The bartack is only there to ensure the running end can't slip out when the line is not under a load ...

Hand tacking refers to pretty much any stitch(es) made by hand, usually using a waxed 5-cord, in order to hold something in place. It can be used in place of a bartack on a line, and we also use it to secure metal ripcord housings to rigs. The waxed 5-cord is also very handy for making eye splices (lashing), especially when one's ability to splice double braid is as lame as mine (I'm working on it tho! :P ).
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Postby GreenLake » Sat May 05, 2012 1:21 am

Tim, thanks for explaining the terms. I was about the ask the same question when @jdoorly beat me to it. All braided line holds the bury by the "fingertrap" technique, nevertheless, that particular word is not standard in splicing literature, or instructions, and I've read quite a few.

What you call "hand tack" is often called cross stitching, or "locking stitches". They don't have to be super strong, because their purpose, as you write, is to hold the splice together when it's not under sufficient load for the outer part to grip the bury.

I often just unravel a foot of line and take a strand or partial strand and use that instead of a yarn for the locking stitches. It blends in very nicely and it has the same stretch characteristics as well as moisture and UV resistance as the rest of the rope. That's something that appeals to me for the purpose, but I'm prepared to learn here and now that this will have awful unintended consequences. :oops:

A Brummel splice interlocks the two lines. It does not rely on the fingertrap principle, the nearest description in human anatomy that I can think of right now would be the mutually clasped hands that you see in any "cliffhanger" movie at the climax. It's not a perfect analogy, and essentially incomplete, but the aspect of mutual and symmetric surround is present.

(In that picture, the fingers of each hand are like the strands of one rope surrounding the other. In a real splice they would not end in fingertips but continue and come together on the other side of the grip in the "tail", which would then be buried in the other rope - somewhere towards the "elbow" so to speak).

If you bury the tails on a Brummel splice, I can't see how it could work itself loose, so there wouldn't seem to be a need for locking stitches.
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Postby K.C. Walker » Sat May 05, 2012 10:13 am

GreenLake

I've read conflicting opinions about where the strength comes from in Brummel splice. The one that makes sense to me is that the double pass through is essentially a knot that locks the splice and that the full strength comes from the bury. Because it is locked no stitching is necessary. Also, because it is locked at just the right place, it does not need a long bury to achieve full strength.
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Postby TIM WEBB » Sat May 05, 2012 11:18 pm

Yeah GL, I think you're right about the terminology: I never heard the term "fingertrap" until I got into skydiving and started working on my rigger's ticket. And I was sailing long before that ... ;-P

What do you mean by "That's something that appeals to me for the purpose, but I'm prepared to learn here and now that this will have awful unintended consequences." ???
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Postby GreenLake » Sun May 06, 2012 2:01 pm

TIM WEBB wrote:I never heard the term "fingertrap" until I got into skydiving...

Could be that terminology is changing while we are watching. If you are familiar with the Chinese finger puzzle, then "fingertrap" is a convenient shorthand. Most sources that I've consulted are still in the stage where they give the analogy, but don't have a shorthand term for it. I think it's interesting how skydiving and mountaineering have developed their own styles of rigging and how some of that slowly feeds back into sailing.

On the sailing anarchy forum there was recently a lively debate on harness styles with interesting input from kite surfers.
What do you mean by "That's something that appeals to me for the purpose, but I'm prepared to learn here and now that this will have awful unintended consequences." ???

Using unraveld strands instead of waxed yarn for lock stitching seems to work, but I haven't tested it exhaustively, and haven't seen it recommended by anyone with real long-term expertise. I think it's a neat way to do it, but I'm not sure whether there are solid reasons, unknown or undiscovered by me, why it might be a bad idea after all. I would not be tempted to use it "bartacking" or wherever there's dependence on the strength of the stitching.
Last edited by GreenLake on Sun May 06, 2012 2:22 pm, edited 1 time in total.
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Postby GreenLake » Sun May 06, 2012 2:18 pm

K.C. Walker wrote:I've read conflicting opinions about where the strength comes from in Brummel splice. The one that makes sense to me is that the double pass through is essentially a knot that locks the splice and that the full strength comes from the bury. Because it is locked no stitching is necessary. Also, because it is locked at just the right place, it does not need a long bury to achieve full strength.


If I had that test rig, that the guy at L-36.com has, I'd be tempted to run out and do a Brummel splice without bury and one with and see which one is stronger, and whether the difference is significant.

Short of that, I can only offer conjecture.

In order for the fingertrap to take up any of the load, it has to not just grip (squeeze) the tail, but pull on it as well after it has gripped it. To do that, it must be able to move, if even a little, away from the interlocking part of the splice. To estimate that effect is difficult, but the outer part of the trap lengthens as it squeezes down and that might provide enough movement to put tension on the inner part.

The holding force is ultimately static friction, which increases with both force and area. If less area is needed, then either some part of the load is taken up elsewhere (in the lock, for example) or otherwise, for the same amount of pull, the force inside the fingertrap is higher.

I could imagine both. The lock is definitely loaded some, and because the fingertrap is therefore pulled at from both ends, it may grip more tightly than one where the upper end is "free floating".

So much for conjecture.
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Postby GreenLake » Sun May 06, 2012 6:22 pm

To pick up on an earlier question:
jdoorly wrote:How do they make these soft shackles so short, my splicing guru demands 12 inches of bury for each eye!

I had claimed that the bury should depend on diameter and further surmised that the locked Brummel can get away with shorter buries. Something like the 12" recommendation comes from using 36 times the rope diameter, and would then be approximately correct for rope of 5/16" diameter. For 3/16" it would be shorter, or approx 7". Now some people use larger factors, for example 48 or 54.

I've found a video on makin an eye in amsteel with minimal tools and in the notes, I found this discussion:
I have tested this extensively using half of each suggested bury length in a locked brummel and all have held while the failure occurs in the line.


I added the emphasis in the quote above. This is the first place where I found that someone had claimed test results for shorter buries on locked Brummels. Although the rest of the information is then a tad confusing on what he actually considers the required lenght of a full bury.

Now, to get back to shackles. With soft shackles that use an openable eye-splice on one end that traps a bulky knot on the other end (see picture), the bury does not actually need the full length, far from it. The reason is that the knot combines strands from both outer and inner rope. Therefore. the shackle does not rely friction in the buyr to keep the two ends of the rope from sliding against each other, as would be the case of a normal eye splice.

Image

Because of that, the way I see it, the bury in this case could be made arbitrarily short and would not be subject to the usual minimum bury distances.
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Postby TIM WEBB » Sun May 06, 2012 9:04 pm

Gotcha GL. Yeah, sailing's been around a lot longer than either skydiving or (I'm pretty sure) mountaineering, but it does seem like it takes a while for more modern techniques to find their way back ...

Here's a method (from our website) of securing a fingertrap without using a bartack:

http://www.jumpshack.com/default.asp?Ca ... tBy=DATE_D
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Postby GreenLake » Mon May 07, 2012 1:17 am

Interesting. If I read the description right you pull the entire tail (and the lower part of the bury) through a hole in the upper part of the bury. That should result in a spot where the splice is turned inside out and right again winding strands of bury (core) and cover around each other .

Always get a twist in the optics trying to visualize what happens. Incidentally, I believe, that kind of tuck is essentially the same as the start for an "inverted" brummel splice, one that can be made in the end of a rope where the other end is not accessible.
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Postby K.C. Walker » Mon May 07, 2012 10:15 am

Green Lake

Here's a video to help with the visuals on that trick. http://www.youtube.com/watch?v=ajc21RsC ... re=related
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