Snorkel
From Free net encyclopedia
A snorkel (also spelled "schnorkel" or "schnorchel") is a tube that allows a person, vehicle, or vessel to draw air while submerged under water.
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Swimmer's snorkel
A swimmer's snorkel is a tube about thirty centimetres (twelve inches) long, usually J-shaped, fitted with a reasonably comfortable mouthpiece, and constructed of rubber or plastic. It is used for breathing air from above the water surface when the mouth and nose are submerged, either during a surface swim before or after scuba diving, or during snorkeling.
The most common type of snorkel is a simple tube that is allowed to flood when underwater. The snorkeller expels water from the snorkel with a sharp exhalation on return to the surface. Some modern snorkels have a sump in the mouthpiece to allow a small volume of water to remain in the snorkel without being inhaled when the diver breathes. Some have a one-way output valve in the sump, which automatically drains the sump as it fills with water. Some snorkels have float-operated valves attached to the surface end of the tube to keep water out when the snorkeller submerges.
The maximum length of the tube is around fifty centimetres (twenty inches). A longer tube would place the lungs in deeper water where the surrounding water pressure is higher and the lungs would be unable to inflate when the diver inhales, because the muscles that expand the lungs are not strong enough to operate against the higher pressure.
Submarine snorkel
Image:USS Chicago (SSN 721) at periscope depth off Malaysia.jpg
A submarine snorkel is also a device that allows a submarine to operate submerged while still taking in air from above the surface. It was invented by the Dutch just before World War II and perfected by the Germans during the war for use by U-boats. Its common military name is snort.
Until the advent of nuclear power, submarines were designed to operate on the surface most of the time and submerge only for evasion or for rare daylight attacks. In 1940, at night, a U-boat was safer on the surface than submerged because ASDIC could detect boats underwater but was almost useless against a surface vessel. However, with the continued improvement in methods of detection and attack, as the war progressed, the U-boat was forced to spend more and more time underwater running on electric motors that gave speeds of only a few knots and with very limited endurance.
The 1940 defeat of the Netherlands by the Wehrmacht was a stroke of luck for the Kriegsmarine. The Dutch had been working on a device that the Germans called the Schnorchel. The Dutch navy had been experimenting as early as 1938 with a simple pipe system on the submarines O-19 and O-20 that enabled them to travel at periscope depth operating on its diesels with almost unlimited underwater range while charging the propulsion batteries.
The Kriegsmarine, at first, gave some consideration to the snorkel as a means to take fresh air into the boats but saw no need to run the diesel engines underwater. In 1943, however, as more U-boats were lost, it was retrofitted to the VIIC and IXC classes and designed into the new XXI and XXIII types.
The first boat to be fitted with a snorkel was U-58 which experimented with the equipment in the Baltic during the summer of 1943. Boats began to use it operationally in early 1944 and by June 1944 about half of the boats stationed in the French bases had snorkels fitted.
On Type VII boats the snorkel folded forward and was stored in a recess on the port side of the hull while on the IX Types the recess was on the starboard side. The XXI and XXIII types both had telescopic masts that rose vertically through the conning tower close to the periscope.
Snorkels created several problems for their users. A U-boat with a snorkel raised was limited to six knots to avoid breaking the tube and its sound detection gear was deafened by the roaring of the air being sucked down the tube. A submarine that stayed underwater for more than a few hours encountered various disposal problems and had to store garbage internally, further fouling boats already infamous for their odors.
Most dramatically, snorkels were equipped with automatic valves to prevent seawater from being sucked into the diesels, but when these valves slammed shut the engines would draw air from the boat itself before shutting down, which was extremely painful to the ears of the crew and sometimes even ruptured eardrums. This last problem still exists in modern submarines, though their larger internal air volume mitigates the pain somewhat.
Modern snorkel induction masts use a fail-safe design consisting of compressed air, controlled by a simple electrical circuit, to hold the "head valve" open against the pull of a powerful spring. Seawater washing over the mast shorts out exposed electrodes on top, breaking the control circuit. This vents the compressed air and allows the head valve to slam shut. When the electrodes are again clear of the water, the circuit is reenergized and the valve reopens.
Vehicle snorkel
Military wheeled vehicles, like Jeeps, are capable of mounting snorkels for the air intake and engine exhaust, to allow them to wade through relatively deep water, limited by the height of the driver's head. In the case of a Jeep, all of the engine openings and wiring are sealed, and the driver must first operate a damper that over-pressures the engine vacuum, to prevent water from entering. After fording, the vehicle's wheel bearings must be repacked by a mechanic.
Such snorkelling equipment is available as an aftermarket accessory for some four wheel drive vehicles. The snorkel is typically routed out through one of the front wings and up beside the "A" pillar to the level of the roofline where it is terminated with either a mushroom intake or a forward-facing intake.
Deep-wading tanks
Many modern tanks and armoured fighting vehicles have snorkel equipment for wading across rivers up to about five metres deep. Deep-wading operations are very dangerous, and not normally attempted unless there is no other alternative.
Western tanks' wading snorkels usually include a wide tube attached to the commander's hatch on the turret. In case the tank stalls under water, the crew can escape through a ladder inside the snorkel. The snorkelling equipment is bulky, and only issued to tank crews when needed. Soviet/Russian/CIS forces use such equipment only as training snorkel. In the field, each tank is normally equipped with two narrow snorkels, and tank crew is issued with rebreathing respirators, in case of emergency.
Wading operations are only attempted where a shallow river bank approach and bottom have been reconnoitred and prepared in advance by engineers. Tanks under water are somewhat buoyant, and tend to turn wildly. Each tank's snorkel has a flag affixed, and the tank company commander remains on the river bank to give navigation orders to each crew as they traverse the river. In the case of the Soviet T-72, a stalled engine means loss of over-pressure, and a quickly flooding engine compart (and subsequently, crew compartment). Underwater escape is extremely hazardous, and crews have been known to panic and drown during training.
Sources
Snorkelling for All, BSAC, ISBN 0091883040
External links
- British Sub-Aqua Club - BSAC Snorkeling
- Snorkel reviews - read user reviews of snorkels from the Scuba Guide. Experienced scuba divers rate and suggest the best snorkels.da:Snorkel
de:Schnorchel fr:Tuba (plongée) ja:シュノーケル nl:Snorkel ru:Шноркель sv:Snorkel