Submarines: Fatal Miscalculation


June 23, 2013: During the construction of a new (S-80) class of submarines in Spain an error was recently discovered. One of the design engineers had made a mistake in calculating the weight of the sub and, as the first one was currently built, it was nearly a hundred tons too heavy. That means, once submerged, the sub would have a difficult time surfacing. Under some conditions (equipment failure or battle damage) it would not be able to resurface at all.

Subs are designed to survive leaks and taking on additional weight (water) while submerged and still be able to resurface. But the unintentional addition of a hundred tons of steel and equipment eliminates much of this margin of safety. The most practical solution is to increase the length of the sub by 5-6 meters (15.5-18.6 feet) thus providing more internal space full of air and buoyancy. This increases the ability of the sub to float. An American firm (Electric Boat) has been hired to help implement this modification, which will delay delivery of the first S-80 sub about two years (to 2017). The modification will increase the cost of the sub about five percent and make the S-80s roomier. That will help crew morale, although the taxpayers are none too pleased with this screw up. 

It was a decade ago that the Spanish navy ordered four S-80 "Scorpene" class subs, at a cost of some $280 million each. Construction didn’t begin until 2007, and the estimated cost grew to $700 million per boat. The S-80 is a Spanish design and features AIP (air-independent propulsion). Modern AIP engines for submarines began to appear in the late 1980s, when Sweden installed Stirling type power plants in their Nacken class subs. The S-80s use a new type of AIP.

The S-80s are 71 meters (233 feet) long, displace 2,200 tons on the surface, have a crew of 32 (plus eight passengers, usually commandos) and are highly automated. The design also concentrates on quietness and a powerful American built electronic sensor and fire control system. The six 533mm (21 inch) torpedo tubes will also be used for mines and cruise missiles. 


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