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Old 19-07-2016, 08:28   #1
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Unveiling Bullseye Strops (eg for low friction rings)

EDITED TO ADD:
I initially calld thse strops "Diamond Strops" after the diamond shape in the centre of the weave. I had concerns though that confusion would reign, as they may be associated with the diamond stopper I used in the first one, not the weave itself.

Dockhead came up a suggestion for the new name in post # 119, that appealed very much, so that is what I would like to call them.

StuM has had a hunt through the Ashley Book of Knots and the weave below may not be listed there. Whether or not it is, this would be a new application I think and the name remains.

Instructions can be found here:
Bullseye soft shackle strop: post #43
Bullseye loop strop: post #14
Bullseye loop strop for twin rings: post #58

To maximise strength the length of the lines in the weave (and for the soft shackle the entire distance from the apex of the noose to the base of the diamond stopper) need to be kept identical, so follow the instructions carefully to achieve this.

The first weaves I made were a bit too loose. The first Bullseye sift shackle strop could also have been shortened a bit (I unnecessarily left longer than 100 mm before forming the Brummel lock). The designs have not otherwise been altered since I made the one below.


CAUTION:
None of the designs here have been tested or at least tested in this application.
I have no expertise in this area, just enthusiasm.
Use at own risk.


Low tension rings are have been used extensively racing for several years now and are creeping into use more and more on cruising vessels, replacing all sorts of standard blocks.

They are made of lightweight aluminium and are strong and inexpensive with no moving parts to fail. Strops using loops of dyneema or dyneema lashings seem to be the most common methods of securing these.

A perfect system for retaining the ring seems elusive, everything has drawbacks (some of them major).
See Dockhead's thread for a long list of possibilities and instructions for a few lashings that could be used:

Down and Dirty Dyneema Strops


Today I find myself needing to attach a low friction ring with a short, removable strop and nothing currently seems to fit the bill , so I have put aside the issue of an ideal lashing for a long strop and have been playing putting something together. The systems of lashing all have so many potential issues that I wanted to see if the strop itself could be used to retain the ring.

I have come up with the Diamond Strop .

Features:
Short (could be a fair bit shorter than illustrated, this was the prototype)
Removable Edited to add: removable while a line is passing through it
Ring retained securely



Not as strong as some other systems, but the advantages I think are significant and there is a use for this short, removable strop.

The end of the stopper could be cut short after pretentioning the strop, but I like the safety of leaving a stump.
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Old 19-07-2016, 09:34   #2
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re: Unveiling Bullseye Strops (eg for low friction rings)

What is the strength of the Diamond strop?

Well, my guess would be the diamond knot is the limiting component in the system, reducing strength by about 46%, as found in Evan's stress tests (invaluable by the way, a huge thanks Evans, as they allow things like this to be developed far more easily).

The throat angle is not super tight, but will also reduce strength. A 1:1 throat will have a strength loss of about 15-20%.

I don't think these strength losses would be cumulative. Is that correct Evans?

One big thing to keep in mind is the means of attachment of the strop. This could lead to significant strength losses.
If the strop is attached to a pad eye and if the thickness of the rod of its loop is the same diameter as a leg of the strop (ie 1:1) then the strength of the line is reduced by 50%. It is worse if the strop becomes thicker, and it often is if it is spliced.

So the loss of strength due to the Diamond knot and throat angle could well be already occurring depending on how you attach your strop.

SWL
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Old 19-07-2016, 09:51   #3
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re: Unveiling Bullseye Strops (eg for low friction rings)

Buy a bigger ring and cow hitch/luggage tag a Dyneema loop to it. Go sailing.
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Old 19-07-2016, 10:08   #4
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re: Unveiling Bullseye Strops (eg for low friction rings)

Quote:
Originally Posted by TheOffice View Post
Buy a bigger ring and cow hitch/luggage tag a Dyneema loop to it. Go sailing.
LOL! You mean I wasted a few hours today?

A bigger ring will not stop the risk of it coming out with flogging. Even an oversized ring needs to be secured.

If 6 mm dyneema is used to make a loop for a strop and is cow hitched, then the minimum length of the system is about 360 mm. Using 8 mm it is about 450 mm. That is not short!

A cow hitch does not make the strop removeable if a line is passing through it.

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PS I AM sailing
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Old 19-07-2016, 17:33   #5
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re: Unveiling Bullseye Strops (eg for low friction rings)

Quote:
Originally Posted by Seaworthy Lass View Post

I don't think these strength losses would be cumulative. Is that correct Evans?

Correct - they do not stack - the weakest point breaks first.

Well, my guess would be the diamond knot is the limiting component in the system, reducing strength by about 46%, as found in Evan's stress tests (invaluable by the way, a huge thanks Evans, as they allow things like this to be developed far more easily).

Correct - I would rate it conservatively at 150% of the dyneema strength. If you used a 'stronger approach' (eg with the tails buried) you move the weak point to the neck and raise the strength to around 220%. But that does make the strop thicker near the knot - which is probably undesirable with this solution because you are cow hitching it near there and it would be twice as bulky (although it would also strengthen the cow hitch)

The throat angle is not super tight, but will also reduce strength. A 1:1 throat will have a strength loss of about 15-20%.

That's a 2:1

If the strop is attached to a pad eye and if the thickness of the rod of its loop is the same diameter as a leg of the strop (ie 1:1) then the strength of the line is reduced by 50%. It is worse if the strop becomes thicker, and it often is if it is spliced.

This is a bit more complicated that that - for instance 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%.
with this design and this application - strength is really not a all that much of a practical issue, because you can always go a size bigger dyneema, until the dyneema gets so thick you have trouble running it thru the padeye - and that will not be a concern for most of our boats - probably not even dockheads.

It seems a good solution. It just leaves the ring banging on the deck as an issue to be solved - I have seen racing boats with circular psa EVA pads under the rings to cushion them.
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Old 19-07-2016, 20:39   #6
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re: Unveiling Bullseye Strops (eg for low friction rings)

Quote:
Originally Posted by estarzinger View Post
If you used a 'stronger approach' (eg with the tails buried) you move the weak point to the neck and raise the strength to around 220%. But that does make the strop thicker near the knot - which is probably undesirable with this solution because you are cow hitching it near there and it would be twice as bulky (although it would also strengthen the cow hitch)
Thanks for the feedback. It is very appreciated.

I couldn't use the stronger approach here with a button stopper, as there was nowhere to bury the legs. The stopper is made immediately after the plait and the ring won't come off to bury the legs. Even if the crossing is made a little looser to allow this, there are loops above the stopper, not a straight run, making a bury difficult. The reason the position of the the loop and stopper can't be reversed, allowing a decent bury, is that the stopper won't pass through the pad eye. Keeping the strop short was a major consideration in the design.


Quote:
Originally Posted by estarzinger View Post
That's a 2:1
Nearly I think. I can't quite achieve 2:1 and keep the ring impossible to remove, but it is pretty close. Making it simply very hard to remove is probably perfectly fine here.


Quote:
Originally Posted by estarzinger View Post
This is a bit more complicated that that - for instance 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%.
with this design and this application - strength is really not a all that much of a practical issue, because you can always go a size bigger dyneema, until the dyneema gets so thick you have trouble running it thru the padeye - and that will not be a concern for most of our boats - probably not even dockheads.
Oh, thanks for the clarification. I had 1:1 fixed in my mind as being fine for dyneema ages ago after your load tests on this, but then something Thinwater wrote about 50% threw me and when I quickly went back to your load testing document last night I just read the first paragraph without going further to the next section on loops .


Quote:
Originally Posted by estarzinger View Post
It seems a good solution. It just leaves the ring banging on the deck as an issue to be solved - I have seen racing boats with circular psa EVA pads under the rings to cushion them.
Yes, the banging is an issue. One big reason a short strop is appealing.
Next step is thinking about padding or some way of making it stand up.

The weaving I have used above can also be used in a continuous loop that would be attached as usual with a cow hitch. I will make up one this morning. There is no strength loss with the stopper then, but the length even when cow hitched is well over twice as long.

In my opinion "short" is valuable and as you wrote, any strength loss can just be made up by going up a bit in dyneema thickness.

I will post photos of the procedure later. While I am still thinking about improvements there is no point spending ages on this right now.

SWL
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Old 19-07-2016, 23:48   #7
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re: Unveiling Bullseye Strops (eg for low friction rings)

Same ring retention system on a loop (ends spliced conventionally with a 72x line diameter bury, tapered over a quarter).

The throat angle of each of the two braids is 2:1, so full strength is maintained. The capture is achieved by the intertwining of the braids.

DIAMOND LONG LOOP STROP

The loop portion needs to be 430 mm long in 6 mm line to accomodate the bury of the tails for the splice:


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Old 20-07-2016, 01:08   #8
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re: Unveiling Bullseye Strops (eg for low friction rings)

SO... am I correct in assuming that the issue in attaching a ring is just something to retain it when the shackle is not in use? To stop it falling out?
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Old 20-07-2016, 01:57   #9
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re: Unveiling Bullseye Strops (eg for low friction rings)

Quote:
Originally Posted by weavis View Post
SO... am I correct in assuming that the issue in attaching a ring is just something to retain it when the shackle is not in use? To stop it falling out?
The issue is when in use. Flogging exerts nasty forces and can twist the ring relative to the strop. When it pops out it is not lost, as the working line threaded through its centre is still there, but the full load is suddenly taken on the strop with no friction ring in place.

SWL
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Old 20-07-2016, 02:08   #10
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re: Unveiling Bullseye Strops (eg for low friction rings)

As you can tell, I just buy all my equipment and dont think about it after that.

So, why not put a backing line on the ring and thread through the shackle on opposite sides. You can then put a high strength zip lock over the shackle and cover with shrink wrap.
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Old 20-07-2016, 02:11   #11
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re: Unveiling Bullseye Strops (eg for low friction rings)

Mechanical, not pretty like your designs.
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Old 20-07-2016, 02:18   #12
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re: Unveiling Bullseye Strops (eg for low friction rings)

Quote:
Originally Posted by weavis View Post
As you can tell, I just buy all my equipment and dont think about it after that.

So, why not put a backing line on the ring and thread through the shackle on opposite sides. You can then put a high strength zip lock over the shackle and cover with shrink wrap.
This would probably work, but there are all sorts of issues. Huge forces are at work. Chafe may be an issue. Degradation with UV will occur.
See Dockhead's thread (link in post #1) where some of the potential problems have been discussed.

There are a host of methods that can be used, but none are ideal.

SWL
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Old 20-07-2016, 04:48   #13
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re: Unveiling Bullseye Strops (eg for low friction rings)

I finally finished the locking stitches on the long strop without a button.
They were a proverbial pain in the *** (I am not fond of using locking stitches).

I did become better and quicker by the time I was getting to the end, but it was very time consuming to do it well.

It is possible to put a Brummel lock on one side as a lock before the long bury splice as above and I will do this next time. The loss in strength is not enough to worry about here. I will have a better look and see if a Brummel is possible for the second bury but I doubt it.

I put some load on it just to see what orientation the weave would take up when in use.

Slight kinks are present, but it all looked good in my opinion. No undue stress except at the cow hitch end.


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Old 20-07-2016, 04:49   #14
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re: Unveiling Bullseye Strops (eg for low friction rings)

CAUTION:
The design below has not been tested.
I have no expertise in this area, just enthusiasm.
Use at own risk.



INSTRUCTIONS FOR THE BULLSEYE LOOP STROP:

Edited to add:
Guide to universal measurements:

End to A = 72 x dyneema line diameter

Edited after 3 made:
A to B: Wind your dyneema snuggly (but not tightly) in the Bullseye pattern around your ring.
I have decided to leave mine so the "artificial" crossing (made where the two loops intersect without any side loading) sits just outside the edge of the ring rim if it will be subjected to flogging. I will make it a bit looser if it is not subjected to this.
Mark where it needs to be locked to maintain this. Unravel and measure between the marks. Average the two measurements. This is the distance you want to leave between A and B.

B to C = appproximately 2 x 72 x 1.2 x dyneema line diameter.
This is the outer portion of the bury. This length allows for bunching up of the outer portion when the tail buries. If you are using a cow hitch and want to increase strength slightly, add enough length to make a cow hitch so that it ends up in an unburied portion of the dyneema to improve bend ratio at the attachment point.

C to D = same as A to B (mark this very accurately)

D to other end = same as end to A


Measurements below are for 6mm dyneema and a low friction ring with an inner hole of 25 mm and inside flange diameter (the bit the dyneema goes around) of 35 mm.

This allows a 72x line diameter bury of the ends in the splices.

• Tape dyneema at the end and at 2340 mm and cut diagonally (makes splicing easier). See edit below.

• Measure 430 mm from the end and mark accurately with a THIN texta. This is A

• Measure 240 mm (adjust for ring size differences) from A and mark. This is B
EDITED TO ADD: this could be a shorter for a snugger fit, 220 seems about right

• Measure 1000 mm from B and mark. This is C

• Mark 240 mm from C and mark. This is D
EDITED TO ADD: this needs to be shorter for a snugger fit, 200 seems about right.
SECOND EDIT: when trialled, 200 seemed too tight for this ring & 6 mm dyneema, 220 looks best, you need to have a play - dont jam it too tight, as you stress the system, but if the strop is subjected to lots of flogging if you make it too loose the ring could be forced out


If you have done this accurately, D will be 430 from the end E

• Lay the dyneema in the following pattern.
Dyneema has a slightly flat profile. I would take a little effort and lay it flat the whole way, not rotating it around. It is pribably not vital, but it all sits just beautifully at the end if you do this and load is probably distributed more evenly.


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Old 20-07-2016, 05:16   #15
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re: Unveiling Bullseye Strops (eg for low friction rings)

Continued:

• Move the loop at the top right under the top left loop as shown below

• Insert the low friction ring in the gap created as shown
Lay the bottom loop in the flange, then the top loop. The loops will lie neatly on top of eavh other.

• Slide the dyneema around until the marks match up as shown
Two loops will now encircle the inside flange of the ring.

Splice the ends in:

• Part the strands on the underside of C with a blunt marlin spike and insert the fid

• Feed the left end emerging at a point half way between C and B

• Pull about 150 mm of the end out and cut the strands to taper evenly over 110 mm

• Carefully pull the tail at the point it inserted until the mark at A appears and tie a temporary tight constrictor knot here with whipping twine.

• Milk the cover over the end

• Repeat with the other side. The only difference is that the insertion point is on the top side of B.

Note the nice diamond shape in the centre of this weave :


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