The boatswain's whistle knot has two leads. You make it from two interlocking underhand loops. It works well as a decorative knot to attach whistles or knives to a lanyard. You can use any type of rope you want but it needs to be about 3/8-inch thick and about 36 inches long. The boatswain's whistle knot is also known as a sailor's knife lanyard knot, a marlingspike lanyard knot, a boatswain whistle knot and a single-strand diamond knot.
Use your left hand to hold the middle of the strand of rope so that the loop to the back of the hand and the two ends are between the fingers and hanging down on the palm.
Make a loop in the end of the rope and hold the loop between your thumb and index finger.
Bring the end hanging down to the left side up through the loop you are holding in your palm.
Bring the same end through the knot again.
Bring the other end through the knot.
Slip the arrangement off your hand and meticulously work the knot into its final form. Make the knot tight.