You might be forgiven for thinking this was a tip about not securing to rotten old tree stumps, but it isn’t. The point to be made is that the knot used is a bowline with a big loop, not a round turn and two half hitches. This is because the crew wanted to be able to flip the line clear when the time came, no matter how hard the wind was blowing. The same holds good if securing to a ring on a pile in a tidal situation. If you’re unlucky and the ring jams at the bottom of the iron stay when the water rises, it can easily end up out of reach. Anyone who’s used a short knot is left high and dry. A long bowline will always make it to the surface.