Dyneema splicing improvisation

[enzo01]

Hello,

I have a situation where I need to splice Dyneema rope, however there is not enough space for a long enough splice. Therefore I created a "lock" as seen on the picture below. If you release the lock you can easily adjust the length of the loop and consequently the length of the rope. Would such a lock significantly weaken the rope strength and/or durability? Any input would be appreciated...

Imgur

IMGUR.COM

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Post with 0 votes and 2 views.

 

[openspaceman]

36 minutes ago, enzo01 said:

Hello,

I have a situation where I need to splice Dyneema rope, however there is not enough space for a long enough splice. Therefore I created a "lock" as seen on the picture below. If you release the lock you can easily adjust the length of the loop and consequently the length of the rope. Would such a lock significantly weaken the rope strength and/or durability? Any input would be appreciated...

Imgur

IMGUR.COM

---

Post with 0 votes and 2 views.

 

I suppose the "lock" passes through both  the live and the tail strands of dynema?

 

The lock will weaken the rope but as you have a loop with 2 lengths then reducing to one thickness my guess is the whole bury and lock is stronger than a single line but less than 200%. of a single line.

[enzo01]

Yes, the "lock" passes through both of them.

 

Your estimation makes sense. 

[Brocky]

Where the tail exits at the bottom would seem to be the weak spot with the sudden change in diameter.  Five to seven locked brummels called a McDonald Brummel splice, with a short two inch bury would be a possibility.

[enzo01]

Locked brummels would make a difficult job to adjust the length of the rope. In my current version this is quite easy, just release the lock and the loop can be adjusted. The rope is part of a sports training tool so this feature to adjust the length of the rope quickly is important. What would be the estimation, how much is Dyneema rope weakened by such a sudden change of diameter (where the tail exits)?

 

I am using 3 mm Dyneema (950 KN) so there should be quite some reserve regarding breaking strength for what I am using it. Hopefully this weak point is not reducing its strength too much--tests should show.

[Brocky]

Coming out the side will reduce the strength by about 20% from what I’ve read.  Another way to make it adjustable would be to try a lock stitch splice, the right number of multiple passes through the rope might create enough friction.  And bury as much as possible, with a stopper knot at the end.

[openspaceman]

13 hours ago, enzo01 said:

I am using 3 mm Dyneema (950 KN)

Check your units, 3mm will survive if you hang  950kg from it not 97 tonne

 

I'd love to see one of those eyes tested to destruction

[Mr. Squirrel]

Is the adjustability of it of key importance? Pulling the lock out and rethreading it looks like a bit of a faff? I would've been tempted to just do a long bury and let it function like an adjustable whoopie splice? If retention of strength is of great importance maybe a few soft shackles of different lengths would do the trick? 

Just some thoughts... 

[enzo01]

20 hours ago, openspaceman said:

Check your units, 3mm will survive if you hang  950kg from it not 97 tonne

 

I'd love to see one of those eyes tested to destruction

Yes, sorry, 950 daN (kg) .

 

Unfortunately I do not have the tools to measure the breaking strength, but might improvise with something just to see where it breaks first.

[enzo01]

1 hour ago, Mr. Squirrel said:

Is the adjustability of it of key importance? Pulling the lock out and rethreading it looks like a bit of a faff? I would've been tempted to just do a long bury and let it function like an adjustable whoopie splice? If retention of strength is of great importance maybe a few soft shackles of different lengths would do the trick? 

Just some thoughts... 

Yes, adjustability (as easy as possible) is the key. The end user needs to have the ability to make the rope longer or shorter for 1 - 2 centimetres.

The problem is that there is no space for a long bury, it can't be more then 7 - 8 cm.

 

@Brocky suggested that at the weak spot, where the tail exits at the bottom, the strength would be reduced by about 20% due to sudden change in diameter. That means that the rope would still have breaking strength of about 760 kg. I think this should be good enough for the application used, but only testing will show.  

Edited August 14, 2020 by enzo01