Lighter, J.E., Random House Dictionary of American Slang volume 1 (A-G)
p.254
bowline n. In phrase: slip (ones's) bowline Near.. to die.   
C.f. syn. slip (one's) cable s.v. CABLE.

1848 in Blair & Meine Half Horse 186; I don't much like to string a feller up in cold blood, and that's what I'd had to done...if he hadn't slipping his own bow-line.



Ashley-Book of Knots p.186. #1010

The BOWLINE, BOWLING, OR BOLIN knot, sometimes called BOWLING's knot. The name is derived from the word Bow Line a rope that holds the leather leech of a square sail.....It is so good a knot, that seldom any sailor will another loop knot aboard ship....It is often said of the devil, "he could make a good sailor if he could only tie a bowline and look aloft.

Sincerely,
Gargoyle

ask a submariner about a "dragon bowline"....a one-handed and one on a bite are lifesaving tools. Lots more in the Ashley book.