THE snorkel was invented long ago by Leonardo da Vinci.
Unfortunately it did not work. It had a hopelessly long tube of around 6m-8m, which meant the diver was unable to draw air down it against the ambient water pressure, and he would have been asphixiated by the build-up of his own exhaled CO2.
The optimum length for a snorkel is about 30cm. This keeps the top well clear of the water when the user is face down, and the column of water that forms once the snorkel has been flooded is easy enough for the user to clear.
Some manufacturers have tried to alleviate the effort of snorkel-clearing with specific design innovations. Some snorkels have valves at the lower end of the tube so the water helps drain it when the snorkeller surfaces. Others have additional drain valves mid-way along the tube to make clearing even easier. The ideal bore is around 2cm, wide enough to allow a sufficient flow of air in without the ingress of water from splashes. A snorkel enables the user to breathe easily at the surface without raising the head from the water, therefore allowing better use of air supply and energy resources.
With mask and fins, it can give a taste of the underwater world for very little cost. For such a remarkably simple bit of kit, even we were surprised to identify more than 90 varieties available at prices ranging from £3 to £30!