How much does a bury affect length?

[Roe Ring]

Calling all experienced cordaholics!!

I have just made a new ridgeline for my BB, including a Dutch biner so it can be disconnected. My main concern was making sure that the finished RL was the same length as the original RL. This sounds simple, and I measured it several times before making the final locked brummel, but it occurred to me that burying the tail of the brummel would shorten the overall line length. I experimented on a spare piece and found that a 6" tail buried shortened the line by about an inch, enough to affect the RL. I adjusted my length and it worked out fine, but I wonder if there is a way of calculating the shortening of the line according to length of bury? I'm thinking of how this might affect loops if I were trying to make them a certain length.

Thanks in advance

Mark

[gmcttr]

I don't have an answer, but your observation tells me why my lengths are always off a little. Duh!

Thanks

[turnerminator]

6" when buried usually works out at 5" as you've found.

Just adding an inch seems the easiest way, or to be more precise, you could add 17% to the length of bury.

Strangely, the ratio is 83% -the same as the ridgeline length.

Spooky huh?

[MAD777]

...Strangely, the ratio is 83% -the same as the ridgeline length.

Spooky huh?

You have now entered - The Twilight Zone!

[DemostiX]

According to Allen Edwards at l-36.com, every hollow cord is different in how much it is shortened by swallowing itself. So hats off to him for measuring the impact of the several size cords for which his calculator makes adjustments.

It would not be that hard for several people to report this for different line. Just bury a good length, say 10" / 25cm, mark the entrance and end of bury, remove the bury, pull tight, and measure the recovered length.

For example

• I just grabbed some gray Amsteel Blue 7/64" and inserted a #7 knitting needle 17" from the end to make hollow the hollow braid.
  
• Then I opened the line toward the end, and stacked the free end on the needle, packing it.
  
• I taped the other end of the hank of cord for the bury..
  
• As I withdrew the needle, I inserted and followed the withdrawal with the taped and untapered bury , all the way to the needle entry point.
  
• I smoothed the sleeve tight onto it, and found the sleeve had swallowed 14 1/4" of bury.
  
• So, that's about 16% shrinkage.
  
• Or 17.25 / 14 = 120% of the un-tapered bury length is required to sleeve it, for this particular cord 7/64" Samson Amsteel Blue.

[nothermark]

Folks should also note that when making a constrictor like a whoopee that you need to allow for the loss in length when marking the entry point. If you want 5 in of contrictor you need to allow 6 inches of line when laying it out. Twice that is probably about right, can't hurt. ;-)