We tried the lashing method with 1/4" Samson Amsteel Dyneema yesterday and the stretch amount was in excess of 1 foot for a 22 foot length. This is on par with the 6.67% Stretch that they show in the Samson application instructions for a 30 foot line at 2 feet of stretch. All in all, that stretch length must be factored into the line length and lashing plan. If not, you will end up with a dramatically under-tensioned rig.
On my second iteration of line length calculation, I undersized the shroud by around 1 foot, but Samson's notes would indicate that the amount should be 1.5 feet (per 22 feet) minimum. There are multiple sources of line elongation including:
-> Constructional Elogation (fibers setting into a tighter bundle)
-> Splice Elongation (strands settings into each splice - 2 in my case, one at each thimbled end)
-> Elastic Elongation (recoverable stretch in the line. recovered when load removed - small for HMPE/Dyneema)
Elongation will increase as loading increases regardless of the line construction.
Shock loading (pulsing of a load) will increase the elongation amount.
Hobie Wire Lengths (Subtract 18 inches from these figure to allow for stretch and lashing setup)
https://static.hobiecat.com/2010_archive/support/pdfs/WireGuide.pdf
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