UV is the Enemy

A neighboring sailor told me he had been told webbing was OK until it bleached white.... I turned white and gasped. I've torn 10-year old sun-bleached climbing slings, still not nearly white, from the mountain with a single bare hand. These are 20 KN slings (4500 pounds).

The reality is that webbing is vulnerable in the sun because it is thin and the UV can penetrate quite deeply.  In fact, these charts understate the problem because the webbing is exposed only on one side (jacklines are turned in use) and because the background on test racks is not as reflective as a white deck. This at least offsets the fact that the racks are in Arizona.

Climbing Ropes, Climbing Slings, Harnesses, Safety Tethers, and Spinnakers. If the item is turned in use so that the sun sees both sides, the deterioration will be slower but will progress farther. A 50% loss in strnegth within 3 years, with only sporadic use, has been documented in the field.

Deck hardware and bearings. Although it can be used for webbing gear, this is unusual. When used for hardware it is heavily doped with carbon black, which prevents UV  penetration. Still, when your jammer levers start to fall apart after 10 years, now you know why.

Polyester Jackline Webbing and Webbing on Sails. Better than nylon, but still serious after a few years. Worse if the sun gets to bot sides, which it will.

The bottom line is that you need to watch both time and condition. I like oversized rope for jacklines, because it holds up far longer, but this is only a solution if you can keep it off the deck.