Soft shackle question
 

I have been using soft shackles recently, and have really enjoyed the way they work. But I am curious if anyone has tried something other than diamond knots in them? The testing seems to indicate a loss of 75% of the strength at the knot, if this could be increased the allowable system loads would jump dramatically.

Weak to be strong
 

Hello,
The trick with soft shackles is to create a toggle without using the dog bones or barrels that other HM shackles do. This means tying some form of knot (a button or lanyard knot), and that necessarily means drastically weakening the rope where the knot is tied.
To compensate for this lack of strength, a soft shackle doubles the mass of rope that goes into forming the knot. Maybe there is some button or lanyard knot which would weaken the rope less, but meanwhile we have a simple, cheap structure at least 1.1 times the strength of the rope it was made from. I'd say that was a really good deal.
Fair leads,
Brion Toss

I can't argue with that Brion, but if there was a different knot that could be substituted for the diamond knot to preserve more strength that would be even better. My question isn't directed at if soft shackles are good enough, they clearly are, and being able to use the same line for a sheet and the shackle it attaches to is nice.

I guess I am just trying to improve a already great system (as compared to metal shackles)

Since Brion and I did the testing and found the large strength loss from the diamond knot, I have been giving this some thought. The only other knot I have tried so far is the Admiralty stopper. It slips. Also, it is not clear to me that it is the knot that is causing the weakness.

Stronger knots have less sharp bends in them. While there is a somewhat sharp bend in the diamond knot, there is a very sharp bend in the shackle itself where the line going through the eye of the shackle takes a sharp bend going through the on its way to the knot. This is either where the shackles fail or very close to it and it may very well be that it is the line going through the eye that fails and not the knot itself. Or it may be a combination.

My boat is at the yard now so that is my focus but I do plan to get back to this. It is a question that is of interest.

That said, having a shackle that is stronger than the line it is made of isn't that bad.

Be sure to check out my improved soft shackle design http://L-36.com/soft_shackle_9.php

Allen
L-36.com

Allen,

I have been following your shackle development pretty closely, and am using a mix of Colligio style soft shackles, and your improved ones. I have to say the improved ones are much nicer, and are the only ones I am making currently. I have been experimenting with a modified diamond knot to try and reduce the bend radius of the line as it enters the knot, but I haven't gotten it worked out well enough to even put it on a bench to see if the knot shape will even work.

I should have some time to play with lines later this week, and if I do I will post some pictures to show you what they look like.

I am fishing them a bit differently though, since I am burying one of the ends coming out of the knot back into the other line. I cat imagine it effects strength, but it does give a cleaner look, and makes it a bit easier to slide the shackle on.

As a general observation, a stronger stopper know would be something like an Admiralty stopper or a fishermans knot. By that I mean a knot where the line makes no bend until it gets to the back of the knot and then works its way forward so that the constricting force that holds the knot does not come from the first part of the knot, but from the last part. I am not sure I am saying this clearly but just think that the line enters the knot straight and goes all the way back and then other parts of the line wrap around and make the knot in some way.

That is why I tried the Admiralty stopper first but as it slipped, it was not a candidate. Many knots slip in HM line. A bowline slips for example. Even the stopper recommended in a Youtube video (that I can't find right now) slips. It may be possible to combine knots to make a good one for this. For example, an Ashley stopper does not slip so perhaps an Admiralty stopper followed by an Ashle stopper.

My boat is having some major work done right now so knot work is on the back burner. I have a spool of Lash-it that I plan on using in my tests. It is weak enough that I can break it with my 30 power winch. It frightens my how much force I need to put on 7/64 line to break it and I can't break 1/8 line without additional purchase.

I was actually thinking about a diamond knot that is inverted, so the line wraps around the back. This way you have a large bend, instead of compression. As I understand the line it has two major weaknesses, compression, and lack of friction. My thought is that by using the body of the knot to absorb some of the load before the compression point it might work better.

Unfortunately I haven't been able to spend the time working on it. Hopefully in the next few days, but I just bought a new boat... So it is outfitting time, and the shackles I have are working fine.....