SNORKELING

Snorkeling is the practice of swimming on or through a body of water while equipped with a diving mask, a shaped tube called a snorkel, and usually fins. In cooler waters, a wetsuit may also be worn. Use of this equipment allows the snorkeler to observe underwater attractions for extended periods of time with relatively little effort.

Snorkeling is a popular recreational activity, particularly at tropical resort and scuba diving locations. The primary appeal is the opportunity to observe underwater life in a natural setting without the complicated equipment and training required for scuba diving. It appeals to all ages because of how little effort there is, and without the exhaled bubbles of scuba-diving equipment.

Snorkeling is also employed by scuba divers when on the surface, and search and rescue teams may snorkel as part of a water-based search. It is also a means to an end in underwater sports such as underwater hockey, underwater rugby and spearfishing.

 

Snorkel

 

A swimmer's snorkel is a tube typically about 30 centimeters long and with an inside diameter of between 1.5 and 2.5 centimeters, usually L- or J-shaped and fitted with a mouthpiece at the lower end, and constructed of rubber or plastic. It is used for breathing air from above the water surface when the wearer's mouth and nose are submerged. The snorkel usually has a piece of rubber that attaches the snorkel to the outside of the strap of the diving mask. An older technique is pushing the snorkel between the mask-strap and the head, but this practice increases the chances the mask will leak.

The optimum design length of the snorkel tube is at most 40 centimetres (about 16 inches). A longer tube would not allow breathing when snorkelling deeper, since it would place the lungs in deeper water where the surrounding water pressure is higher. The lungs would then be unable to inflate when the snorkeler inhales, because the muscles that expand the lungs are not strong enough to operate against the higher pressure.

Snorkels also constitute respiratory dead space. When the user takes in a fresh breath, some of the previously exhaled air which remains in the snorkel is recycled into the lungs, reducing breathing efficiency and causing a build up of carbon dioxide in the blood, which can result in hypercapnia. The greater the volume of the tube, and the smaller the tidal volume of breathing, the more this problem is exacerbated. A smaller diameter tube reduces the dead volume, but also increases resistance to airflow and so increases the work of breathing. Occasional exhalation through the nose while snorkeling will reduce the build up of carbon dioxide, as well as helping to keep the mask clear of water.

Flooding and clearing

 

The most common type of snorkel is a simple tube that is allowed to flood when underwater. The snorkeler expels water from the snorkel either with a sharp exhalation on return to the surface (blast clearing) or by tilting the head back shortly before reaching the surface and exhaling until reaching or breaking the surface (displacement method) and facing forward again before inhaling the next breath. The displacement method expels water by displacing its presence in the snorkel with air; it is technique that takes practice but clears the snorkel with less effort, but only works when surfacing. Clearing splash water while at the surface requires blast clearing.

Some snorkels have a sump in the mouthpiece to allow a small volume of water to remain in the snorkel without being inhaled when the snorkeler breathes. Some also have a one-way output valve in the sump, which automatically drains the sump as it fills with water. A few snorkels have float-operated valves attached to the top end of the tube to keep water out when a wave passes, but these cause problems when diving as the snorkel must then be equalised, using part of the diver's inhaled air supply. Some recent designs have a splash deflector on the top end that directs any water that splashes over the open tube to the outside of the tube, thereby keeping the tube relatively free from water. A common problem with all assistive mechanical clearing mechanisms is their tendency to fail due to infrequent use, long periods of storage, and lack of maintenance, and also to fail due to environmental fouling.

Natural rubber slowly oxidizes and breaks down due to ultraviolet light exposure from the sun. It eventually loses its flexibility, becomes brittle and cracks. This causes one-way clearing valves to stick in the open or closed position, and float valves to leak water due to a failure of the valve seat to seal out water. It is unlikely that natural rubber is still used for any part of a snorkel. Silicone rubber is more resistant to degrading and so tends to have a longer service life. Application of a grease to the valve seats can aid in sealing, but this is mechanically washed away over time, and a heavy grease can cause valves to stick closed and trap grit, which will cause the valve to leak.

Environmental fouling can be caused by beach sand or loose floating plant or animal matter getting lodged in the valves and preventing proper opening or closing. Although swimming with a snorkel is much easier than without, it is important that a novice swimmer also learns surface breathing and floating without a snorkel, in the event that these assistive clearing mechanisms fail. If either the sump clearing valve sticks open or the top float valve sticks closed, a snorkel is rendered useless as a breathing aid and the swimmer is forced to fall back on alternative surface breathing methods.
 

Some snorkels used to be made with small "ping pong" balls in a cage mounted to the open end of the tube to prevent water ingress, but these are no longer sold nor recommended to be used since they are considered hazardous to the snorkeler. Similarly, diving masks with a snorkel built into them are considered unsafe and obsolete.