Bathyscaphe

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Typical internal arrangement

A bathyscape, bathyscaphe, or bathyscaph is a free-diving self-propelled deep-sea diving submersible, consisting of a crew cabin similar to a bathysphere suspended below a float (rather than from a surface cable, as in the classic bathysphere design). The float is filled with petrol because this is readily available, buoyant, and incompressible. Buoyancy can be trimmed easily by replacing petrol with water or by dropping ballast, and the incompressiblity of the petrol means the tanks can be lightly constructed as they are not required to withstand significant pressure.

To descend, a bathyscaphe floods air tanks, but unlike a submarine the water in the flooded tanks cannot be displaced with compressed air to ascend, because water pressures are typically too great. Instead, ballast in the form of iron shot is released to ascend, the shot being lost to the ocean floor. The iron shot containers are in the form of one or more hoppers which are open at the bottom throughout the dive, the iron shot being held in place by an electromagnet at the neck. This is a failsafe device as it requires no power to ascend; in fact, in the event of a power failure, shot runs out by gravity and ascent is automatic.

Auguste Piccard, inventor of the first bathyscaphe, composed the name bathyscaphe using the Greek words "bathos" (depth) and "skaphos" (ship).

The first bathyscape was dubbed FNRS-2, named after the Fonds National de la Recherche Scientifique, and built in Belgium between 1946-48 by Piccard. Propulsion was provided by battery-driven electric motors.

Piccard's second bathyscaphe was Trieste, which was purchased by the U.S. Navy in 1957. It had two water tanks and held 120,000 litres of petrol in eleven tanks for buoyancy [1]. In 1960 Trieste, carrying Piccard's son and a U.S. Naval officer, set a world record by diving to a depth of 35,810 feet (10 915 metres) at the bottom of the Challenger Deep, the deepest point in the Mariana Trench and believed to be the deepest point in the world's oceans.