As you well Know Kendall, "the Chains" are an arrangement of ropework and sometimes chain that held the leadsman at an angle of about 45 degrees protruding over the ships side, (Starboard if right handed Port if left handed) and secured him so that he had both hands free, he could then use his "good hand" to "heave the lead" forrard along the line of motion of the ship, letting the line pay out between the fingers of his other hand,the marker in his hand when the line went slack indicating the depth of the water, each fathom had a distinctive marker of different texture so that it could be held to the lips , if it was cold or dark , and be recognised by the leadsman.