Sentence:  The torpedo method was to arrange ten torpedoes on the port side, placed outside abreast the bulkheads and the cargo-hatches so as to give the maximum sinking effect to a breach opened up by each, the torpedoes being carrie by a fore-and-aft belt-line extending along the outside from end to end about twelve feet below water, each torpedo, in addition, having a hogging-line, or <WSD>girthline</WSD>, extending around underneath the keel, for holding the torpedo in its place. 
Meaning of the word marked with <WSD> tags:  A rope or cable that attaches around the girth of something.