Not so broadly
messenger as precisely (two functions -- flight
and *messengering*)
heaving line, I'd say. And 6mm/0.25"
PP ought to be amply light (I'm trying to recall what examples of
such things I've seen; I don't think any much thinner, and maybe
of heavier fibre). (I regard this general function of a thinner line
bringing over a thicker/heavier line to entail a sub-class of knots
called "messenger-line hitches" (or "bends", taken in historical
sense of "joint"; "hitch" in the sense of tying the thinner
oneto the other in contrast to the two lines playing equally in the knotting).
Can you heave some part of the coil, as well as launching the knob?
I recall one local fellow who assisted in a semi-annual (I think)
movement of the USS Constellation, and he'd been advised on
heaving that the big sin was to drop it short, in the drink; his
attempt in fact went the other direction in missing the mark
and made some loud BANG on hitting an (unoccupied) chair.

--dl*
====