All yachts should carry a simple mask and snorkel for that evil day when the propeller gets wrapped up. Flippers are good too, but not essential. Cutting the shaft free of fishing tackle, mooring ropes or even the skipper’s underwear is not difficult for a swimmer armed with a serrated blade such as a good bread knife or a hacksaw. But you must be able to see what you’re doing. A few quid spent in a seaside store could save a lifeboat call-out.