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Pontoon


Photograph of Seabees assembling prefabricated pontoons
Naval Historical Center #80-G-45671

A pontoon is a flotation device. Pontoons were used on seaplanes in place of wheels to allow takeoff and landing from water. Portable pontoons were used in a bewildering variety of ways in applications ranging from barges to small floating dry docks.

The U.S. Navy's Seabees were equipped with a mass-produced prefabricated pontoon which, when assembled at an advanced base, took the form of a 5' by 7' by 5' (1.5m by 2.1m by 1.5m) sheet metal box, weighing about 2600 pounds (1200 kg), with fittings that allowed it to be filled with water, pumped dry with compressed air, and connected to other pontoons. This became the Lego of the Pacific War. Joined together in lengths of two units by up to 35 units, they formed a portable causeway that could be towed or ported by an LST. Assembled into a platform three units wide by seven long, it became a 50-ton barge, which could be propelled by an outboard motor. 48 units could be assembled into a small floating dry dock, capable of repairing small craft such as PT boats. Pontoons could even be assembled into a stable base for a 40-ton crane. Like Marson mat, a pontoon construct could be quickly repaired by unlatching the damaged sections and replacing them with new pontoons. Engineers constructed pontoon causeways at Okinawa, the largest of which was 1428' long with a pierhead 45' by 175'.

The design originated with Captain John Laycock of the Navy's Construction Engineer Corps in 1940. However, it was not obvious how to produce a metal box with sufficient buoyancy and strength at an affordable cost. Laycock experimented with cigar boxes and had a feasible design by February 1941. The first experimental models and accompanying outboard motors were tested in the spring of 1941, and British observers were so delighted that they ordered 3000 units at $700 each. By 1944 production had exceeded 10,000 a year.

References
Huie (1944)

Leckie (1995)



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