Britain's Largest Flying Boat Launched -- Britain's largest flying boat, the four engine Short-Saro Shetland, was launched at Rochester today. The aircraft, which can carry 70 passengers with a crew of 11, has a maximum speed of 267-m.p.h. The flying boat has a wing span of 150 feet, a length of 110 feet and an all up weight of 130,000 lbs. It has a range of 4,650 miles cruising at a speed of 184 m.p.h., and is a civil version of the Shetland designed during the war for service purposes. Two de