Down and Dirty Dyneema Strops

[Seaworthy Lass]

Originally Posted by Dockhead

OK, so you're saying that you are abandoning the stitched buries, and want to go to a Grog type bury with interlocked brummels?

FWIW, my Grog type strops are holding up fine so far under many tonnes of load.

No, not a Grog sling. Still a conventional long bury splice.
There are two ways of securing these though. With a proper Brummel lock or with locking stitches. The Brummel lock is a piece of cake when you have access to two free ends, as you know. I use this for eye splices in dyneema. It think you have used it this way too?

It is not possible to use a Brummel lock conventionally in a loop. The Grog sling starts with a proper Brummel but then to bury the ends you need to flip the ends around 180° producing something that is not longer a proper Brummel.

The reason why one can be used in this Diamond weave arrangement it that you make half of the Brummel lock, then weave the pattern then the tail ends up in the right spot for a bury. I think this can only be done once though. The other leg will need locking stitches still.

SWL

[Seaworthy Lass]

Dockhead, I am posting instructions in the Diamond strop thread, as they are buried here and in time will be very difficult to find.

I have put the first lot in.

SWL

[estarzinger]

Just FYI - the grog semi-brumel bury is NOT a lock - it still needs to be stitched to absolutely prevent low load slipping possibility. The grog semi Brummel is there to add friction to allow a shorter bury, but it can in fact be pulled apart by hand (unlike a "real" Brummel.

on stitching - just two thoughts (1) it helps if you "scrunch up" (eg push the braid toward itself) the braid before trying to thread thru (each time you want to go thru). (2) I actually use a "para-cord fid" to push a hole thru before using blunt needle. The para-cord fid is a quite small diameter blunt fid.

[Seaworthy Lass]

Originally Posted by estarzinger

Just FYI - the grog semi-brumel bury is NOT a lock - it still needs to be stitched to absolutely prevent low load slipping possibility. The grog semi Brummel is there to add friction to allow a shorter bury, but it can in fact be pulled apart by hand (unlike a "real" Brummel.

Evans, unlike an unlocked bury splice, this kind of slippage is extremely unlikely. The starting point is a proper lock so if you tug on the "eye", which is in this case the main loop, the loop is locked.
What could happen would be if curious little fingers played with the insertion point of the end and somehow managed to pull out the buried end. If this join is put at the top of the low friction ring in the flange, or at the bottom in the cow hitch, this can't occur.

Even if the ends are pulled out, the loop could not be parted by hand. The issue of the ends being coaxed out manually could even occur with a real Brummel, although not as easily, as the junction is flat.

Originally Posted by estarzinger

on stitching - just two thoughts (1) it helps if you "scrunch up" (eg push the braid toward itself) the braid before trying to thread thru (each time you want to go thru). (2) I actually use a "para-cord fid" to push a hole thru before using blunt needle. The para-cord fid is a quite small diameter blunt fid.

Thanks for that tip. I didn't try scrunching, as I didn't want to disturb the milking.

I am probably whinging too much about the locking stitches. It was inevitable .

SWL

[estarzinger]

Originally Posted by Seaworthy Lass

Evans, unlike an unlocked bury splice, this kind of slippage is extremely unlikely. The starting point is a proper lock so if you tug on the "eye", which is in this case the main loop, the loop is locked.

If I remember correctly when I tested for Grog - what can happen is that the grog lock can 'invert' so that it is no longer locked - which cannot happen with the real Brummel (because the direction of pull on the real brummel is different - parallel rather than 180 degrees) I do not remember the sequence of events exactly - was quite a while ago - but there is a definite failure mode and it does need to be sewn.

I could probably dig up photos from my e-mail correspondence with grog during this testing.

Now how "unlikely" this is I can't say - as you know I believe if it can happen, it will, and probably at the worst possible time.

[estarzinger]

I just looked up my e-mails - and in 6mm dyneema - the grog lock without the bury pulled apart at 330lbs - it inverted and came apart. So it absolutely depends on the friction of the bury to hold it together.



This is technically called 'ring loading failure' - it is a different loading orientation than loops in the ends of lines are usually put to. It is known as a 'trap' in climbing and heavy lifting, where you use something that is perfect in 'normal' use but will fail at load load in ring loading.

in bowline loops - you use the Eskimo bowline rather than the conventional one when you are going to have ring loading.

[estarzinger]

This is a grog sling with burried but not sewn tails coming apart. With a very slow/low steady pull.



the lock has inverted and one tail has pulled out, and it is just sliding apart now.

This is testing I did April 2014.

[Dockhead]

Originally Posted by estarzinger

This is a grog sling with burried but not sewn tails coming apart. With a very slow/low steady pull.

Attachment 128119

the lock has inverted and one tail has pulled out, and it is just sliding apart now.

This is testing I did April 2014.

How many pounds of force?

So I guess I need to sew up the tails of all of mine (6 of them so far)?

I've been sailing with them a few miles now and are all still intact.

[Seaworthy Lass]

Originally Posted by Dockhead

How many pounds of force?

So I guess I need to sew up the tails of all of mine (6 of them so far)?

I've been sailing with them a few miles now and are all still intact.

Dockhead, i doubt it is much of an issue with the lock at the top of the ring.

Evans, I really can't see how it could be pulled apart by hand.

SWL

Edited to add: In the Grog sling with the cow hitch that I posted a photo of in your soft shackle thread I put the join at the cow hitch end. This will help clamp it I think.
If its integrity is an concern then you could reverse the position of the join and put it there. This would mean your strops would not go to waste. Only the lacing would need to be remade.
See what Evans says. Stitching may be safer. It will give you lots of practice at least!

[RDW]

in post 89 with the pictures, look at the other end. The concern as I read is the acute angle around the ring but look at the other end. I am not experience and just reading to pick up some knowledge. Is not the other end just as important??
RDW

[Seaworthy Lass]

Originally Posted by RDW

in post 89 with the pictures, look at the other end. The concern as I read is the acute angle around the ring but look at the other end. I am not experience and just reading to pick up some knowledge. Is not the other end just as important??
RDW

Comment from Evans about this:

Originally Posted by estarzinger

..... if a loop is around a 1:1 padeye, the strength is 100% (or 95%). But if that loop is around a payeye in a cowhitch it would be 85%.

15% is not as much loss in strength as you would expect given how stressed the dyneema looks in a cow hitch. Dyneema handles sharp bends incredibly well.

It of course helps to have loops with a thick diameter to cowhitch to.

Dockhead, how thick are your padeye loops?

SWL

[estarzinger]

Originally Posted by Dockhead

How many pounds of force?

in the photo above it was 2000lbs, but it depended on the bury - you have long buries, which will absorb a lot of force before the lock will invert. I seem to remember that grog had a target of 50% of the dyneema strength or better (so equal to a bend or better) and we concluded he needed 30 dia buries or longer (30 may not be exactly right but is in the right ballpark - he would have the specific number on his page or on my site). Your loops with 72x buries are probably completely secure, especially after being loaded like they have been. But there may be a scenario of a low cyclic load combined with a high cyclic shock load that would allow it to slip a bit and invert - even a small amount of stitching would stop that - stitch tensile = 330lbs would be an absolute guarantee. And yes I agree with SL there are probably places in the sling for the lock that would be more resistant to this than others, but none would be as absolutely sure as stitching.

Originally Posted by Seaworthy Lass

Dockhead, i doubt it is much of an issue with the lock at the top of the ring.

Evans, I really can't see how it could be pulled apart by hand.

agreed, unless you can pull 330lbs with your bare hands . The lock does need to get "inverted" before it will slide more easily, so there is this "hump load" needed to get over - which is smallish in sailing load terms but yes certainly not hand pull-able.

As I mentioned in our PM's, I had/have forgotten quite a bit about the grog sling testing and results - I just remembered that neither Allen nor I really liked it and we both discouraged grog from making a big deal of it. I would have to go back and read thru about 50 emails to get fully back up to speed on it. Given we have better solutions for both long and short strops I don't really see taking the time to do that unless someone is really curious. He really wanted to get something that allowed much shorter buries and this allowed it, but it was neither as strong nor as secure as alternatives (long bury & soft shackle & multiple loops folded)

...............

[Seaworthy Lass]

Originally Posted by estarzinger

As I mentioned in our PM's, I had/have forgotten quite a bit about the grog sling testing and results - I just remembered that neither Allen nor I really liked it and we both discouraged grog from making a big deal of it. I would have to go back and read thru about 50 emails to get fully back up to speed on it. Given we have better solutions for both long and short strops I don't really see taking the time to do that unless someone is really curious. He really wanted to get something that allowed much shorter buries and this allowed it, but it was neither as strong nor as secure as alternatives (long bury & soft shackle & multiple loops folded)

Very useful info. I have not previously read anything negative like this regarding the Grog sling. With the short bury needed to give its maximum strength (and from memory this was not that much weaker than a standard loop), and the lack of stitching it was very appealing.

I will avoid using it .

SWL

[Dockhead]

Originally Posted by Seaworthy Lass

. . .

Dockhead, how thick are your padeye loops?

SWL

8mm, the same as my Dyneema.

[Seaworthy Lass]

Dockhead, I am feeling bad that I suggested a Grog sling earlier and you made half a dozen .

As you don't have much dyneema left, but still have have of summer left to cruise, I would stitch them to be safe. No harm in doing this. Maybe one by one when you have some leisure time? The bonus is that your stitching skills will improve tremendously.

SWL