Unveiling the BB Soft Shackle

[Seaworthy Lass]

Originally Posted by estarzinger

^^ - I 'close' the soft shackle - into a loop, using the soft shackles own noose - when putting the tension on - there is no slipping and it tightens up everything evenly - just as it would be in use.

I assumed the pretensioning would need to be done with the shackle open so that the load was even on the stopper. The load distribution would be quite different if the shackle was secured the other way (the loop can be brought around to reach the stopper in two ways).

Hence the struggle with how to do this .

SWL

[estarzinger]

Originally Posted by Seaworthy Lass

The load distribution would be quite different if the shackle was secured the other way (the loop can be brought around to reach the stopper in two ways).

No. I tested it (by breaking the shackle in "the opposite way"). It makes no difference to the breaking strength.

[Seaworthy Lass]

Originally Posted by estarzinger

No. I tested it (by breaking the shackle in "the opposite way"). It makes no difference.

Well that makes pretensioning dead easy on board then .

I will do this for the last BB I made (post #49) and put it into use.

It will be interesting to see how much the stopper has moved on the BB that has been on the chain during this past week. We have had calm conditions the last couple of days, but it was gusting 20-30 for a couple of days prior to that.
I marked the base of the Button so that I will be able to easily check this.

SWL

[SailFastTri]

You've got me thinking...

In my bridle I use Dyneema loops to form a Prussic knot around the rope rode. It doesn't slide.

I could probably substitute a long soft shackle wrapped 3 or 4 times around the rope rode, with similar gripping effect, under load.

[jcapo]

Originally Posted by estarzinger

^^ - I 'close' the soft shackle - into a loop, using the soft shackles own noose - when putting the tension on - there is no slipping and it tightens up everything evenly - just as it would be in use.

I've done it that way also. I'm after much tighter knots than I can create when pulling with the shackle closed.

[estarzinger]

Originally Posted by jcapo

I'm after much tighter knots than I can create when pulling with the shackle closed.

Mmm . . . . Well, I can pull the shackle right up to breaking strength when it is closed . . . . And in every design, except the 'stronger' design, the weak/breaking point is the base of the stopper knot . . . So there is no way to get it tighter than that.

Now if you are saying you just don't have the equipment to pull hard enough, and so want to eliminate the 1:2 purchase of the closed shackle, in order to get more pressure on the stopper with your limited pulling power . . . . Ok I would suggest the easiest way to make a straight line pull is to make up two small dyneema pieces (1) with a noose on one end and a bigger loop on the other - put the noose around the stopper you want to pull - tie your puller rope to the bigger loop, and (2) a second piece with two decent size loops - thread it thru the shackle noose loop and tie your other puller line to those bigger loops. The is easy to diy and easy to store and relatively inexpensive.

Or as I suggested above . . . . Get a simple cheap hydraulic body shop puller and then you can put as much pressure on the soft shackles as you could ever want, right up to breaking them when they are closed.

[CAELESTIS]

Here are some photos of 1/4 and 5/16 shackles. The first is with the knot as tight as I can get it (large screwdrivers thru each loop and pulling enough to hurt my back). The second is with the Harken 74 primary treatment. Note the small sharpie marks on the pre and post stressed knots. This is why locking the knot is important. Last photo shows the pre stressed shackles with long tails spliced into a loop, and ready for the winch.

[Seaworthy Lass]

The first 6mm BB soft shackle (post #30) linking the snubber to chain was in use for 11 days. After an initial tightening by only pulling by hand with a marlin spike then with the Button held in a vice, the Button shifted 4 mm underwater as it tightened up under load. We have had calm weather this last week (a respite after a windier than usual October), but had a couple of days of 20-30 knot gusts while it was in use initially.

I will put this BB aside now and start using the latest version (post #49) when we drop anchor this evening. The difference between the two shackles is the latest has a total lack of locks adjacent to the central bury, and the shackle had a "proper" pretension using the winch, although the Button did not shift much during this procedure.

This shows the movement of the Button that occurred while the first 6mm BB was in use underwater (see post#31 for underwater photos). The white string marker was initially right under the base:

http://i1377.photobucket.com/albums/...ps3vfecwzn.jpg

So far so good . Lets see how the latest performs over the next month.

[Seaworthy Lass]

During our passage today I pre-tensioned the latest BB soft shackle from post #49, which was tightened first by hand a few days ago with a marlin spike, then while secured in a vice. The pre-tensioning was simply done with the shackle closed, winched and left to sit for 20 minutes, as Evans suggested.
I attached it to a bowline loop slung on one winch and a bowline tied at the end of the lazy sheet leading to a Lewmar 54 dual speed winch. I cranked this slowly to the maximum amount I was capable of, before letting it sit for 20 min. Thankfully we were on a delicious broad reach so no tacking was required .

This is the shackle lightly secured:

http://i1377.photobucket.com/albums/...psdodnq27z.jpg


And here it has load applied and is 'sitting' for 20 min:

http://i1377.photobucket.com/albums/...psn3ds2bu8.jpg

We are now smack in the middle of the Cyclades and this BB was just deployed. The wind frequently rips down the centre of the Aegean so over the next few weeks we should get some decent loads on it to test it out .

SWL

[Seaworthy Lass]

By the way, I marked the base of the Button before tensioning this last shackle. I was absolutely amazed to find one side did not shift at all after being winched. The unmarked side shifted a few mm. It is not symmetrical, as the load was applied to the button in the shackle's closed state. It will be interesting to see if any further shift occurs while in use between the snubber and chain.

The slightly skewed Button after being tensioned with a winch. The Amsteel becomes quite stiff after this treatment. The white thread at the base of the Button is the marker:

http://i1377.photobucket.com/albums/...psashpju6t.jpg

[estarzinger]

You need some prettier colored dyneema

You seem to do a pretty good job with your spike and washer. Do you figure you are putting 25 kgs on your #54 winch handle - that would probably be 'sufficient' but is still a relatively small fraction of breaking strength (1/4?)

[Seaworthy Lass]

Originally Posted by estarzinger

You need some prettier colored dyneema

You seem to do a pretty good job with your spike and washer. Do you figure you are putting 25 kgs on your #54 winch handle?

The spike is what really tensions it. Three pulls are needed for each tail to go all the way around, plus the final pull of the tail through the centre. The first pull can only be lightish as otherwise the standing end is yanked on. The next two I pull with all my strength. A considerable amount of slack is taken up (a cm or two). There is barely any movement of the Button on the vice after that.

I have no idea what force I can physically apply on the winch. "A fair bit" is my best estimate . I will try a 2:1 purchase next time and see if I can get the Button to move any further.

SWL

[estarzinger]

^^ I think it is theoretically worth trying for 50% breaking strength in pretension. But I did not test this design for pre-tension sensitivity - only the diamond stopper - which can suck the tail in if the pre-tension is too low and the tail cut too short.

But what do you figure your max anchor snubber loads are? I am sure one of you has thought about it a bit 1500kgs? if so, then your winching is already getting you near max working load and that surely 'enough'.

You are not going to suck the tails back into the stopper with this design, so I guess it's really a matter of making sure there is not enough heat build up inside the stopper (with a bunch of slipping/tightening) in a snatch load to weaken the dyneema. The water will obviously help dissipate the heat so this is a 'safer' application than some others, but I believe you could still get melting inside the dyneema if there was a lot of movement.

[Seaworthy Lass]

Originally Posted by estarzinger

^^ I think it is theoretically worth trying for 50% breaking strength in pretension. But I did not test this design for pre-tension sensitivity - only the diamond stopper - which can suck the tail in if the pre-tension is too low and the tail cut too short.

But what do you figure your max anchor snubber loads are? I am sure one of you has thought about it a bit 1500kgs? if so, then your winching is already getting you near max working load and that surely 'enough'.

You are not going to suck the tails back into the stopper with this design, so I guess it's really a matter of making sure there is not enough heat build up inside the stopper (with a bunch of slipping/tightening) in a snatch load to weaken the dyneema. The water will obviously help dissipate the heat so this is a 'safer' application than some others, but I believe you could still get melting inside the dyneema if there was a lot of movement.

The soft shackles used over the last 18 months have withstood gusts of 50-55 knots for prolonged periods so if I take a wind speed of 60 knots and use Knox's formula, then 3300 lb = 1500 kg force is the estimated load. Using the ABYC data (said to be overestimated) it is 6200 lb = 2800 kg force.

We use 14mm nylon for the snubber (16mm may be more appropriate with stronger wind, but 14mm stretches more and provides better cushioning for general use). Brand new and dry the min breaking force (static) of 14mm nylon is 7200 lb. In 6mm Amsteel, it is 13,500 lb for the soft shackle. The nylon is the weak point in our system, but regardless, I would like the soft shackle capable of optimal performance.

My aim with the careful hand tightening of the soft shackle has been to try and eliminate the possibility of a large amount of movement when sudden force is applied. I have seem how badly many knots perform when not dressed well. Scarily so! What I haven't paid attention to is making sure a brand new soft shackle has not been used for the first time in rough conditions. I think it would benefit "seasoning" a new one gently if it is not pretensioned on a winch.

I will get a better feel for the adequacy of the force I can apply using our winch once I have seen how much further these Buttons move while in action. I have never pretensioned one on a winch before, so at the moment anything is better than nothing .

In future I would really like to pretension the BB open, not closed (that uneven tension on the Button bothers me, even though that is how load is eventually applied) and I will do this next year when I get hold of more Amsteel and can make up a couple of lengths with eye splices on each end. I can pop on 2-3 washers (I think just one will bend) to ensure the load is even and this will have the added benefit of a nice flat base resulting on the Button.
Given the slight shift of the Button that will occur as load is applied, I wonder if I should wait to bury the tails after the winching, allowing them to be fed into the core as close as possible to the base of the Button. It will also mean the bury will not interfere with the pretensioning. What do you think?

SWL
PS The BB has been given the thumbs up from the user on the bow . The feedback is that the lack of tail sticking out of the stopper makes them much easier to operate.

[estarzinger]

Originally Posted by Seaworthy Lass

In future I would really like to pretension the BB open, not closed (that uneven tension on the Button bothers me, even though that is how load is eventually applied) and I will do this next year when I get hold of more Amsteel and can make up a couple of lengths with eye splices on each end. I can pop on 2-3 washers (I think just one will bend) to ensure the load is even and this will have the added benefit of a nice flat base resulting on the Button.

Theoretically I think it is optimal to pre-tension it in the 'actual use' condition (eg closed shackle). So that the two strands are evenly pulled at the angle they will actually be used. If you pre-tension it in the open orientation, then in the closed orientation in-use one strand may take all the load rather than sharing it evenly. Again, in theory, if you want to pre-tension it in the open orientation, it might make sense to not tension it up too high, so there is a little self-adjustment movement left in the actual use orientation. BUT I doubt it makes much difference in real world practice - its going to break at the first tight compression/bend in the knot in either case So, if you prefer the complete symmetry, go for it


Given the slight shift of the Button that will occur as load is applied, I wonder if I should wait to bury the tails after the winching, allowing them to be fed into the core as close as possible to the base of the Button. It will also mean the bury will not interfere with the pretensioning. What do you think?

Yes, I agree, bury after pre-tension - but then put it under tension again to help lock the bury. . . . and then sew the bury.

SWL
PS The BB has been given the thumbs up from the user on the bow . The feedback is that the lack of tail sticking out of the stopper makes them much easier to operate.

It is an elegant design.

If we ever get a bit more space I might set my test rig back up - you have raised some interesting new questions that I might be able to test - I have a couple ideas how I could modify my rig to get tighter results and more repeatability.

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