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| Home >> Technical >> Dyneema loop tang for kicker |
27/03/2020 22:18:00
david
Posts: 64
A couple of pics would be helpful to the rest of us. Having trouble picturing what you guys are saying.
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27/03/2020 22:16:00
david
Posts: 64
Hi Jonathan,
I would expect some bedding in of the diamond knot under load but perhaps not 2" each side. However, even a bedding in of 2" should not make it unusable. You just adjust the other knots in the system, there is still plenty of range. If you want to keep the system the same for 3 rigs you could add an extra cow hitch or turn around the shackle or loop to reduce any difference, or use no cow hitch on one of the rigs, the cow hitch is not critical (although the benefit is reducing the load on the dyneema and never losing your shackle). For example, I have a cow hitch on my 9 & 7 rigs and am aware that I might not need one with my 5 rig with the slightly higher boom, if I am to avoid adjusting the rest of the system.
You could;
- Try to pull the diamond knot tight as you go. Use pliers if necessary.
- Make the tail a little under length on anticipation of some bedding in. You can initially attach the shackle without a cow hitch. After initially applying tight vang to bed the knot in you will then be able to tie a cow hitch around the shackle. That is how I have experienced them supplied recently. I could only just at a struggle tie the cow hitch before the first sail, which is perfect.
- A simple home bimble alternative to the diamond knot is to tie the original double overhand knot and thread the two tails between the knot and the washer. Tests by Selden showed this to be very effective at minimising any slippage from with the double overhand knot. (See photo in this thread)
Adding the Dog Bone fitting is not permitted in the Class Rules. It is not necessary or recommended.
Locking splices will dramatically reduce the breaking strength of the dyneema as you load those strands at that point. That main kicker strop takes a huge load so must not be compromised.
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I would expect some bedding in of the diamond knot under load but perhaps not 2" each side. However, even a bedding in of 2" should not make it unusable. You just adjust the other knots in the system, there is still plenty of range. If you want to keep the system the same for 3 rigs you could add an extra cow hitch or turn around the shackle or loop to reduce any difference, or use no cow hitch on one of the rigs, the cow hitch is not critical (although the benefit is reducing the load on the dyneema and never losing your shackle). For example, I have a cow hitch on my 9 & 7 rigs and am aware that I might not need one with my 5 rig with the slightly higher boom, if I am to avoid adjusting the rest of the system.
You could;
- Try to pull the diamond knot tight as you go. Use pliers if necessary.
- Make the tail a little under length on anticipation of some bedding in. You can initially attach the shackle without a cow hitch. After initially applying tight vang to bed the knot in you will then be able to tie a cow hitch around the shackle. That is how I have experienced them supplied recently. I could only just at a struggle tie the cow hitch before the first sail, which is perfect.
- A simple home bimble alternative to the diamond knot is to tie the original double overhand knot and thread the two tails between the knot and the washer. Tests by Selden showed this to be very effective at minimising any slippage from with the double overhand knot. (See photo in this thread)
Adding the Dog Bone fitting is not permitted in the Class Rules. It is not necessary or recommended.
Locking splices will dramatically reduce the breaking strength of the dyneema as you load those strands at that point. That main kicker strop takes a huge load so must not be compromised.
Reply
26/03/2020 16:35:00
Peter Barton
Posts: 4664
From Jonathan Rickels,
I tried the Diamond Knot on all three rigs, and despite tightening as much as I could before inserting in the masts on a 1st sail with the 9 rig in light wind found the loop extended by two inches; so far that I couldn't get the boom horizontal for good upwind sailing.
It seems that the multiple loops within the Diamond Knot slip & tighten substantially when full sailing loads are applied. Which makes it very difficult to tie the knot with a loop so short that it will then stretch to the desired length, and this be repeatable across rigs. Hanging the loop off a hook and attaching weights was suggested, but not an option.
Using a 'Dog Bone' and splicing the Dyneema, using a lock splice, was suggested as a better alternative.
There are plenty of aluminium Dog Bones available, but being wary of the long term corrosion effects of Al on the stainless steel washer went for a stainless steel Dog Bone that is more Dumb Bell shaped.
By pre-tiing the Cow Hitch around the shackle and lock splices before and after the Dumb Bell found I could set the length of the loop precisely. The trailing lock splice was followed with a normal dyneema splice; one tail fed down inside the other.
Each was pre-sailing stressed by placing lower mast in boat, attaching boom and kicker / vang purchase, and putting tension on hard with the boom over my shoulder.
So far No slip or stretch.
Unfortunately due Covid-19 have not been able to sail, both myself and boat are in lockdown.
And I would have put some pictures in this post, but don't have any means to shrink the resolution sufficiently.
It seems that the multiple loops within the Diamond Knot slip & tighten substantially when full sailing loads are applied. Which makes it very difficult to tie the knot with a loop so short that it will then stretch to the desired length, and this be repeatable across rigs. Hanging the loop off a hook and attaching weights was suggested, but not an option.
Using a 'Dog Bone' and splicing the Dyneema, using a lock splice, was suggested as a better alternative.
There are plenty of aluminium Dog Bones available, but being wary of the long term corrosion effects of Al on the stainless steel washer went for a stainless steel Dog Bone that is more Dumb Bell shaped.
By pre-tiing the Cow Hitch around the shackle and lock splices before and after the Dumb Bell found I could set the length of the loop precisely. The trailing lock splice was followed with a normal dyneema splice; one tail fed down inside the other.
Each was pre-sailing stressed by placing lower mast in boat, attaching boom and kicker / vang purchase, and putting tension on hard with the boom over my shoulder.
So far No slip or stretch.
Unfortunately due Covid-19 have not been able to sail, both myself and boat are in lockdown.
And I would have put some pictures in this post, but don't have any means to shrink the resolution sufficiently.
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26/03/2020 16:25:00
Peter Barton
Posts: 4664
28/08/2019 19:49:00
Andy Butler
Posts: 19
28/08/2019 17:48:00
Hairsy
Posts: 44
Hi Dave,
The shorter the loop the better so you have maximum range in the kicker/vang system. Just enough to do a Cow Hitch (otherwise known as a Larks Foot) over the round end of the shackle is perfect. A 60mm long loop after pulling the knot tight (measured double and pulled straight) is about the minimum you need.
Don't tie the Cow Hitch over the pin of the shackle as the dyneema can get caught in the screw thread and deform. 
If you are unable to tie a Diamond knot (see video link) then the original double overhand knot with both tails tucked back in between the knot and the washer would seem to half any initial slippage, although not quite as effective as a Diamond knot.
Always remember to use the bent washer to spread the load on the inside wall of the mast.
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The length of loop and type of knot are not controlled by the rules.
The spec is;
600mm of 5mm dyneema, a 28mm M8 curved washer and a diamond knot.
The new standard from Selden is a Diamond knot inside the mast behind the bent washer. This knot reduces any slippage.
Be sure to pull the knot as tight as you can (use pliers if necessary) and leave long tails behind (e.g. 100mm) to be safe.The shorter the loop the better so you have maximum range in the kicker/vang system. Just enough to do a Cow Hitch (otherwise known as a Larks Foot) over the round end of the shackle is perfect. A 60mm long loop after pulling the knot tight (measured double and pulled straight) is about the minimum you need.Don't tie the Cow Hitch over the pin of the shackle as the dyneema can get caught in the screw thread and deform.
The benefit of the cow hitch is reducing the load on the dyneema and never losing your shackle. If you have more than 1 rig it is then nice to have a shackle attached to each rig for simplicity.
If you are unable to tie a Diamond knot (see video link) then the original double overhand knot with both tails tucked back in between the knot and the washer would seem to half any initial slippage, although not quite as effective as a Diamond knot. Always remember to use the bent washer to spread the load on the inside wall of the mast.
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28/08/2019 17:03:00
Peter Barton
Posts: 4664
Thank you Peter. I’ve ordered dyneema.
It comes as a simple length. Does anyone have a lower mast handy and able to measure the length of the loop?
I dont want to fall foul of rules by having a non standard loop!
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28/08/2019 08:08:00
Hairsy
Posts: 44
Hi Dave,
Contact RS for a replacement loop.
Chop off the old one (unless you can push it out intact)
Pull the new one through with a thin strong mousing line.
Be sure to fit the existing bent washer behind the new tang's knot to spread the load (this is vital).
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27/08/2019 23:37:00
Peter Barton
Posts: 4664
I had a thought - does this have an inner that takes the load and, if so, could the inner have given way and I'm now left with the outer which is why it's now longer?
I've added a picture from inside the mast in case that helps - I assume this is what I should expect it to look like.
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26/08/2019 16:11:00
Hairsy
Posts: 44
Although I can't be sure, I think the dyneema loop for my kicker has slipped. It is 14.5 cm long and I'm fairly sure it was shorter than that. Picture below.
Can anyone confirm whether this is too long? If so, Can I pull it out and put a knot in it and then reinsert or does it need a more sophisticated fix or replacement?
Many thanks
Dave
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26/08/2019 16:08:00
Hairsy
Posts: 44
