I have been thinking about since a bow-stuff in the recent Newport-Ensenada race caused my crewmate to fly around the bow of our I20, breaking the spinnaker pole and ending the race for us.
A search on Google found this link:
http://www.scouts.asn.au/knots_ad.html"A knot used by climbers. It is made with a strop (endless loop, either spliced or tied) round the main climbing rope. It can be loosened and slid along the rope to vary its position on the rope."
It looks like you just loop the "chicken line" (the one with the carabiner) around the "jack line" (the fore-aft one) twice.
I'm definitely getting some version of this on my boat, as I have often wished I had something similar when ocean sailing in good winds.
Sail fast and have fun,
Alan Thompson
I20 - San Diego