viernes, 28 de junio de 2013

Uso de Rebreather y Pecio HMS Victoria

Muy buenas,
El tema viene de la charla que nos ofreció ayer Mikel Zabaleta sobre la exploración de la cueva del Forat de l’Or:
Mikel me comentaba, como anécdota, el uso del Rebreather para bajar a los 130 ms del HMS Victoria, en el Líbano.

Un poco de info al respecto:

-Rebreather (o Reciclador):
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment.

Rebreather technology may be used where breathing gas supply is limited, such as underwater or in space, where the environment is toxic or hypoxic, as in firefighting, mine rescue and high altitude operations, or where the breathing gas is specially enriched or contains expensive components, such as helium diluent or anaesthetic gases.

As self contained breathing apparatus – where it is variously known as "closed circuit scuba", "closed circuit rebreather" (CCR), "semi-closed scuba", "semi-closed rebreather" (SCR), "closed circuit underwater breathing apparatus" (CCUBA - a military term), or just "rebreather", as opposed to "open circuit scuba" where the diver exhales breathing gas into the surrounding water.

Mixed gas rebreathers for diving:

Semi-closed circuit rebreathers used for diving may use active or passive gas addition, and the gas addition systems may be depth compensated. They use a mixed supply gas with a higher oxygen fraction than the steady state loop gas mixture. Usually only one gas mixture is used, but it is possible to switch gas mixtures during a dive to extend the available depth range of some SCRs.
Rebreather diving is underwater diving using rebreathers which recirculate the air already used by the diver after replacing oxygen used by the diver and removing the carbon dioxide metabolic product. Rebreather diving is used by recreational, military and scientific divers where is has advantages over open circuit scuba, and surface supply of breathing gas is impracticable.

Basic principle:

At shallow depths, a diver using open-circuit breathing apparatus typically only uses about a quarter of the oxygen in the air that is breathed in, which is about 4 to 5% of the inspired volume. The remaining oxygen is exhaled along with nitrogen and carbon dioxide - about 95% of the volume. As the diver goes deeper, much the same mass of oxygen is used, which represents an increasingly smaller fraction of the inhaled gas. Since only a small part of the oxygen, and virtually none of the inert gas is consumed, every exhaled breath from an open-circuit scuba set represents at least 95% wasted potentially useful gas volume, which has to be replaced from the breathing gas supply.

A rebreather recirculates the exhaled gas for re-use and does not discharge it immediately to the surroundings. The inert gas and unused oxygen is kept for reuse, and the rebreather adds gas to replace the oxygen that was consumed, and removes the carbon dioxide. Thus, the gas in the rebreather's circuit remains breathable and supports life and the diver needs only carry a fraction of the gas that would be needed for an open-circuit system. The saving is proportional to the ambient pressure, so is greater for deeper dives, and is particularly significant when expensive mixtures containing helium are used as the inert gas diluent. The rebreather also adds gas to compensate for compression when depth increases, and vents gas to prvent overexpansion when depth decreases.
-Pecio HMS Victoria:
HMS Victoria was the lead ship in her class of two battleships of the Royal Navy. On 22 June 1893, she collided with Camperdown near Tripoli, Lebanon during manoeuvres and quickly sank, taking 358 crew with her, including the commander of the British Mediterranean Fleet, Vice-Admiral Sir George Tryon. One of the survivors was second-in-command, John Jellicoe, later commander-in-chief of the British Grand Fleet at the Battle of Jutland.

Displacement: 11,020 long tons (11,200 t)
Length: 340 ft (100 m)
Beam: 70 ft (21 m)
Draught: 26 ft 9 in (8.15 m)

After a search that lasted ten years, the wreck was discovered on 22 August 2004 in 150 metres of water by a Lebanese diver called Christian Francis. She stands vertically with her bow and some 30 metres of her length buried in the mud and her stern pointing directly upwards towards the surface. This position is not unique among shipwrecks as first thought, as the Russian monitor Rusalka also rests like this. The unusual attitude of this wreck is thought to have been due to the heavy single turret forward containing the main armament coupled with the still-turning propellers driving the wreck downwards.

Mismo video en Youtube:

Video del que me hablaba Mikel: 

Diving The Wreck of HMS Victoria, Lebanon por phil_grigg

Impresionante descenso hacia la popa:

Actualización a 13/06/2014: Ayer Mikel Zabaleta (quien ya nos dió una charla en Buceo Donosti sobre la exploración de la cueva del Forat de l’Or y en quien me inspiré para escribir esta entrada) nos dió una charla sobre Rebreathers y volvió a comentar varios temas de los que, en su momento, recogí en esta entrada.
Más info:

Ah! Y el video que nos mencionó (y que ya recogí en su momento) donde se les ve colocando las botellas en el cabo mientras bajan lo más rápido posible para aprovechar el tiempo de fondo:
Nota: La inmersión comienza en el 14:00, el pecio se empieza a ver en el 19:15, penetración en el 28:00, ascenso en el 38:00 y se acaba con las paradas.

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