The Bimini twist is the strongest knot for forming a loop in heavy monofilament. Big game anglers use it to form a double line to which the leader is attached. IGFA Angling rules allow a double line up to 30 feet and this can allow extra pressure to be applied to a big blue marlin or bluefin tuna once a few turns of double line are wound onto the reel. Alternative knots which can be used are the the Aussie plait or the Spider hitch for light tackle applications.
1) Begin by making a loop and twist the line at least 20 times.
Depending on the length you wish to make the double, two people may be required.