Thursday, May 15, 2014

Wire Cable vs. Stanchions

Over at Sail Delmarva Drew puts the test equipment he has built to work investigating the ability of various recommended lifeline materials to resist chafe thru the stanchions...
I've been investigating chafe protection and Amsteel as it relates to lifeline replacement. Certainly, wire cable is the gold standard. But now I'm not so sure....

After an hour of sawing back-and-forth through a 10mm hole in SS tubing, it had eaten a nice groove and built a corresponding burr on the inside:

After 1 hour.

And though the wire did not look very worn, when we flexed just a bit there was a different story....

Also 1 hour. The damage was not apparent until flexed. Most of the broken wires were inside.

How did Amsteel fare, in the same hole? Before the wire created the burr? Much better with very little wear in an hour. Afterwards, no as well, but still the damage was little more serious than that to the stainless cable. Given that I plan to use 1/4 Amsteel, which is nearly twice as strong as the cable to start with, I'm feeling OK. 1/4-inch it is sufficiently strong that even after 10 years in the Chesapeake sun (not so strong as the desert southwest or tropics) it should have equivalent strength, and with proper chafe guards, the strength loss in the holes should be less than wire. Protected from the sun, the pass-troughs may be the strongest part by then.

How does Amsteel like the new hole? Not so bad as you might think and about the same as it like the raw hole, just after I drilled it without deburring. By way of comparison, after the hole was deburred it showed ~ 1/3 this much wear, and if coated with Spinlock RP25, no wear after 2 hours (840 cycles).

After 1 hour on the wire cable gouged hole. About the same as a raw drilled hole, yet much worse than a polished hole.

Alternatively, I tried a dyneema anti-chafe sleeve floating for 3 hours. It could have run for 100 hours without showing wear.

A floating dyneema cover reduces wear to zero.

By way of comparison, this hole wore a polyester line through the cover in 20 seconds and in half in 5 minutes. Amsteel is tough stuff.

1 comment:

  1. Testing continues, using a pendulum with heavy pressure in place of an oscillating motion with light pressure; the results are VERY different. SS cable excels in this new test, while fiber materials slice through on a saw cut edge in relatively few cycles. The lessons learned for fiber lifelines are these:
    * Hole prep is a must. Polish with 600 grit paper, since any burrs are deadly.
    * At least 5mm core. Any less can cut on sharp ferrules under heavy pressure.
    * Chafe guards are a requirement. Chafe is worse than it looks with HMPE lines. Any local chafe is too much.

    Why do we say HMPE line is vulnerable to chafe, the opposite of conventional wisdom? Because with localized chafe, it is far more prone to sudden failure than polyester or nylon. Why? With conventional materials, each yarn carries load according to it's ability. Wounded yarns stretch more and carry less. With HMPE all yarns carry equal load, the wounded yarns fails first, and a rapid cascade takes out the rest. Not a theory--we tested 20% chafed lines at 35% strength. We then cut 70% cleanly from several yarns in new line (88% total remaining) and saw failures at 35%. This is NOT the behavior we see in polyester.


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