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.

Swimmers snorkel with splash guard on top, but with no sump valve.

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.

  

 Snorkeler underwater, with snorkel's sump valve apparent in foreground.

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.

The dive mask

Snorkelers normally wear the same kind of mask as those worn by scuba divers. By creating an airspace, the mask enables the snorkeler to see clearly underwater. All scuba diving masks consist of the lenses also known as a faceplate, a comfortable skirt, which also encloses the nose, and a head strap. There are different styles and shapes. These range from oval shaped models to lower internal volume masks and may be made from different materials; common choices are silicone and rubber.

The practice of snorkeling

 

Snorkeler with mask and snorkel.

Although donning a mask and snorkel and swimming in any body of water would technically constitute "snorkeling," by and large it is generally accepted that a "snorkeler" would don such gear and practice such activity within the vicinity of a reef, wreck, or other submerged objects, either to observe aquatic organisms including fish, algae, etc. or to look at rock formations. Being non-competitive, snorkeling is considered more a leisure activity than a sport.

Snorkeling requires no special training, only the ability to swim and to breathe through the snorkel. However, for safety reasons, instruction and orientation from a fellow "experienced" snorkeler, tour guide, dive shop, or equipment-rental shop is recommended. Instruction generally covers equipment usage, basic safety, what to look for, and what to look out for, and conservation instructions (fragile organisms such as coral are easily damaged by divers and snorkelers). As with scuba-diving it is always recommended that one not snorkel alone, but rather with a "buddy", a guide or a tour group.

Some commercial snorkeling locations require snorkelers to wear an inflatable vest, similar to a personal flotation device. They are usually bright yellow or orange and have a device that allows users to inflate or deflate the device to adjust their buoyancy. However these devices hinder and prevent a snorkeler from free diving to any depth. Especially in cooler water, a wetsuit of appropriate thickness and coverage may be worn; wetsuits do provide some buoyancy without as much resistance to submersion. In the tropics, snorkelers (especially those with pale skin) often wear a rashguard or a shirt and/or board shorts in order to help protect the skin of the back and upper legs against sunburn.

Experienced snorkelers often start to investigate amateur free-diving, which should be preceded by at least some training from a dive instructor or experienced free-diver.

Safety precautions

The greatest danger to snorkelers are inshore and leisure crafts such as jet skis, speed boats and the like. A snorkeler is often submerged in the water with only the tube visible above the surface. Since these crafts can ply the same areas snorkelers visit, the chance for accidental collisions exist. Sailboats and windsurfers are especially worrisome as their quiet propulsion systems indicates that a snorkeler may be unaware of their presence, unlike any motor-driven craft, as sound travels farther underwater. A snorkeler may surface underneath one and/or be struck by such vessels. Few places demarcate small craft areas from snorkelers, unlike for regular bathers who may have areas marked by buoys. Snorkelers may therefore choose to wear bright or highly reflective colors/outfits and/or to employ dive flags to utilize being spotted easily by boaters and others. On the other hand, some snorklers may use camouflage in order to surprise unsuspecting visitors.

Snorkelers' backs can be exposed to the sun for extended periods and can burn badly (even if slightly submerged), without being noticed. Wearing appropriate covering such as a "rash guard" (in warmer waters), a t-shirt, a wetsuit and/or sunblock will mitigate the risk of sunburn.

Dehydration is another concern. Hydrating well before going in the water is recommended, especially if one intends to snorkel for several hours. Proper hydration also prevents cramps.

Snorkelers can experience hyperventilation, which can lead in turn to “shallow water blackout″; snorkeling with a buddy (and being aware of the buddy's condition at all times) can help avoid this situation.

When snorkeling on or near coral reefs, care must be exercised to avoid contact with the delicate (and sometimes sharp and/or stinging) coral and its poisonous inhabitants, usually via protective gloves and by being careful of one's environment. Booties and surf shoes are especially useful as they allow trekking over reefs exposed by low tide, to drop offs or deeper waters of the outer reef.

Also, for ecological reasons, contact with coral always should be avoided because even boulder corals are fragile. A soft touch can cause decades worth of growth to be undone in mere seconds, and the coral may never recover.

Snorkeling locations

 

Snorkelers observing fish in Cozumel, Mexico.

Snorkeling is possible in almost any body of water, but snorkelers are most likely to be found in locations where there are minimal waves, warm water, and something particularly interesting to see near the surface.

Generally shallow reefs ranging from sea level to 1 to 4 meters (3 to 12 feet) are favored by snorkelers. Deeper reefs are also good, but repeated breath holding to dive to those depths limit the number of practitioners and raises the bar on fitness and skill level.

More Snorkel

Source :

http://en.wikipedia.org/wiki/Snorkeling
Snorkel