Rope Stretch

[cat49]

If you go to New England Ropes website and look at the PDF files for the different ropes it shows how much rope stretches at different percentages to tensile strenght.......alot of the polyester ropes stretch more than nylon. and it shows Double Braided nylon with the most stretch of anything...

[estarzinger]

Originally Posted by cat49

If you go to New England Ropes website and look at the PDF files for the different ropes it shows how much rope stretches at different percentages to tensile strenght.......alot of the polyester ropes stretch more than nylon. and it shows Double Braided nylon with the most stretch of anything...

New England ropes have an error in their nylon 3 strand graph - I think it was copied accidentally from their stayset pdf. Its been there for a while.

Below I have compared the stretch numbers for similar ropes from Yale and NEw England ropes.

Stretch at 20% of breaking load
Nylon brait Yale:13% New England Rope: 11%
Nylon 3 strand Yale: 9%, New England Rope: 2% = error
Nylon double braid 8%, New England Rope: 9%
Polyester double braid 4%, New England Rope: 2%

[lancelot9898]

Originally Posted by estarzinger

New England ropes have an error in their nylon 3 strand graph - I think it was copied accidentally from their stayset pdf. Its been there for a while.

Below I have compared the stretch numbers for similar ropes from Yale and NEw England ropes.

Stretch at 20% of breaking load
Nylon brait Yale:13% New England Rope: 11%
Nylon 3 strand Yale: 9%, New England Rope: 2% = error
Nylon double braid 8%, New England Rope: 9%
Polyester double braid 4%, New England Rope: 2%

I always thought that the 3 strand had a lot more stretch than the double braid, but from the table above it doesn't appear to be much different.(9 vs. 8)

While the stretch characterics of the line has shock absorbing benefits there are some negatives too in the case of extreme conditions. My first and final time aboard at anchorage(with a single anchor) in a cat 1 hurricane saw some interesting sling shot effects as the gusts hit the boat. Like a rubber band on a recoil.

Another comment about stretch is the amount of stretch that a line sees as one goes beyond the 20% number. I suspect that the amount of stretch stays pretty constant from 20% of breaking load on up to actual breaking, but have no data to back it up. Also it would be interesting to see the actual diameter reduction related to the stretch since that can be measured while the line is under load. The rope manufactures surely have these numbers and also should have data related to ageing effects, but getting these numbers may be hard.

[cfarrar]

About three issues ago Practical Sailor did a nice evaluation of commonly used lines from Sampson, New England Ropes, and Yale. They looked at strength, stretch, handling, chafe resistance, and cost. Here's a link, but you have to pay $10 unless you're a subscriber: Testers Examine Running Rigging