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Abathyscaphe (/ˈbæθɪˌskeɪf,-ˌskæf/) is afree-diving, self-propelleddeep-seasubmersible, consisting of a crew cabin similar to abathysphere, but suspended below a float rather than from a surface cable, as in the classic bathysphere design.[1]
The float is filled withgasoline because it is readily available, buoyant, and, for all practical purposes, incompressible. The incompressibility of the gasoline means the tanks can be very lightly constructed, since the pressure inside and outside the tanks equalizes, eliminating any differential. By contrast, the crew cabin must withstand a huge pressure differential and is massively built.Buoyancy at the surface can be trimmed easily by replacing gasoline in the tanks with water, because water has a greater density.
Auguste Piccard, inventor of the first bathyscaphe, coined the namebathyscaphe using theAncient Greek wordsβαθύς (bathús), meaning 'deep', andσκάφος (skáphos), meaning 'vessel, ship'.
To descend, a bathyscaphe floods air tanks with sea water, but unlike asubmarine the water in the flooded tanks cannot be displaced with compressed air to ascend, because the water pressures at the depths for which the craft was designed to operate are too great. For example, the pressure at the bottom of theChallenger Deep is more than seven times that in a standard "H-type" compressedgas cylinder. Instead, ballast in the form ofiron 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 afail-safe 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.
The first bathyscaphe was dubbedFNRS-2, named after theFonds National de la Recherche Scientifique, and built inBelgium from 1946 to 1948 byAuguste Piccard. (FNRS-1 had been the balloon used for Piccard's ascent into the stratosphere in 1938). Propulsion was provided bybattery-drivenelectric motors.[1] The float held 37,850 litres (8,330 imp gal; 10,000 US gal) of aviation gasoline. There was no access tunnel; the sphere had to be loaded and unloaded while on deck. The first journeys were detailed in theJacques Cousteau bookThe Silent World. As described in the book, "the vessel had serenely endured the pressure of the depths, but had been destroyed in a minor squall".FNRS-3 was a new submersible, using the crew sphere from the damagedFNRS-2, and a new larger 75,700 litres (16,700 imp gal; 20,000 US gal) float.
Piccard's second bathyscaphe was actually a third vesselTrieste, which was purchased by theUnited States Navy fromItaly in 1957.[1] It had two water ballast tanks and eleven buoyancy tanks holding 120,000 litres (26,000 imp gal; 32,000 US gal) of gasoline.[2]
In 1960Trieste, carrying Piccard's sonJacques Piccard andDon Walsh, reached the deepest known point on the Earth's surface, theChallenger Deep, in theMariana Trench in the Pacific Ocean.[1]
The onboard systems indicated a depth of 37,800 ft (11,521 m) but this was later corrected to 35,813 ft (10,916 m) by taking into account variations arising from salinity and temperature. Later and more accurate measurements made in 1995 have found the Challenger Deep to be slightly shallower at 35,798 ft (10,911 m).
The crew of theTrieste, which was equipped with a powerful light, noted that the seafloor consisted ofdiatomaceous ooze and reported observing "some type of flatfish, resembling asole, about 1 foot long and 6 inches across" (30 by 15 cm) lying on the seabed.[3] This put to rest the question of whether or not there was life at such a depth in the complete absence of light.
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