In response to my puzzlement about a piece of rigging on the USS Constellation we encountered while on vacation, a reader writes:
Check out Baggywrinkle – just an idea about your ‘shaggy ropes.’
And, indeed, that must be it. Wikipedia:
Baggywrinkle is a soft covering for cables (or any other obstructions) to reduce sailchafe. There are many points in the rig of a large sailing ship where the sails come into contact with the standing rigging; unprotected sails would soon develop holes at the points of contact. Baggywrinkle provides a softer wearing surface for the sail.
The lower specimen appears to be an exact match to what we saw. Thanks!