Page:Popular Science Monthly Volume 92.djvu/417

 Launching Concrete Boats Bottom Up

Norwegians are shipbuilders of old. Now they've devised a new way of building and launching vessels

��LAUNCHING a two -hundred -ton concrete vessel bottom up may sound fantastic, but it has recently been done with success by a ship- building company in Norway. The vessel was a rein- forced con- crete lighter (concrete strength- ened by a skeleton of steel strips), and consis- ted of an in- ner hull of wood which served as a mould for the whole

structure. When completed, there rested upon the launching ways the inner wooden mould, divided into watertight compartments, and the outer concrete

���Though launched bottom form inside, the big boat

��hull, both bottom up. An inner compart- ment was left open at the bottom, so that water entered as the vessel left the

ways, the air escaping through pipes in the hull. When this com- partment was com- pletely flooded', the water then reached the level of the two upper side com- partments, causing the boat to lose its buoyancy and su b - merge to a position of unstable equilibrium. In this position,. a slight list to one side caused the boat to heel over completely and float to a normal position.

��side up, and with a wooden slid smoothly into the water

����Position A shows the boat just entering the water, the wooden form inside, and all of its water- tight compartments full of air. In position B — water has entered the center compartment and also those along the bottom, the air escaping through vents. At C — the two lowest compartments, closed to the water, are buoying up on the boat and causing it to turn over. Drawings D and E show further stages. The water is afterward pumped out

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