Quite a lot of sailing has given me a good appreciation of knots. It's amazing how (when you're doing a lot of rope work) you can get a real instinctive sense of the pressures on a knot and how to create the best knot for the situation. In ocean racing there are places you have unusual needs (like tethering the running backstays to the cars while you adjust the angles).
Believe it or (k)not, there a branch of mathematical topology dedicated to knot theory.