Friday, January 25, 2013

FLOATING DOCKS


            Floating docks offer great flexibility. These units ride the waves and work satisfactorily in areas of negligible to significant water level variation. Floating docks are commonly referred to as "floats," not to be confused with aircraft floats.
Design Concepts. A small float, 10 by 15 feet (3 by 4.5 m), designed to support loads up to
2,500 pounds (1 134 kg), will handle a single plane. Larger floats intended for mooring two or more aircraft should be designed to support gross loads up to 5,000 pounds (2 268 kg). Floats as narrow as 7 feet (2 m) can be used where a long, floating dock parallelsthe shore. Floats are usually constructed from locally available materials.
 Dimensions. Float dimensions are determined by the number of aircraft simultaneously
using or projected to use the float. The design aircraf length plus 20 feet (6 m) clearance both fore and aft is recommended where aircraft are to be docked or moored alongside the float. A float should be wide enough for planes to dock on each side with a 10 foot (3 m) minimum clearance between wingtips.
Flotation. A variety of materials have been used to provide buoyancy for floating docks, e.g., logs, milled timber, polystyrene billets, fiberglass, and steel containers.
(1) Polystyrene billets have proven to be satisfactory buoyancy devices for floats. The planks
should be evenly distributed, rather than piled at concentrated points, under the superstructure. A barrier of 6 mil (.15 mm) black polyethylene sheeting should be placed between all treated timber and flotation material contact surfaces. The load supporting characteristics of polystyrene or styrofoam is approximately 50 pounds per cubic foot (800 kilograms per cubic meter) of material. A common billet size is 10 inches by 20 inches (25 by 50 cm) by 9 feet (3 m). Further data on this material may be obtained from the manufacturers. It is
recommended that foam planks be enclosed with woven galvanized wire to prevent damage from aquatic animals and sea gulls. Polystyrene deteriorates when exposed to petroleum products, gas spills, etc.
(2) Fifty-five gallon steel drums are commonly used as flotation devices. Drums should be
placed symmetrically around the perimeter of the float to ensure stability. They are fastened to the float by steel straps of sufficient length to extend around the drum and main framing members of the float. Foam, fiberglass, plywood boxes, and steel drum floats are susceptible to damage where deadheads or strong currents prevail. Steel drums have a short life expectancy in salt water. The pilot should be aware of the corrosive affect of galvanic action caused by dissimilar metals. Securing the aircraft to steel or metal drums, by a chain or wire
rope, will start a galvanic action that will corrode the aluminum floats. Satisfactory floats can be improvised by using life rafts, small floating docks, pontoons, and similar devices which can be obtained in the open market.
(3) Where relatively large and straight timber is available, logs may be used to construct a rafttype float.
Devices. A continuous 4 by 4 inch (10 cm by 10 cm) wood rail, raised approximately
2 inches (5 cm) above the float deck, commonly called bull rail or tie rail, is recommended. Bull rails should be secured by long lagbolts to dock cross-members or logs. Cleats should be provided, approximately 5 feet (1.5 m) apart, along the bull rail or sides of the float. Corner
posts should extended slightly above the deck to serve as bollards. Bumpers, installed along the sides of the structure, extending below the edge of the float sufficient length to prevent damage to aircraft floats, are recommended.
Combined Float/Ramps. Floats equipped with ramps at each end make good operational structures where amphibian aircraft are to be accommodated. A long, narrow float with ramps on both sides is adequate for mooring or tieing down light, single-engine floatplanes. A ramp incline no steeper than 8:1 is recommended. The aircraft taxi onto the ramp and are
pulled up and tied down to the ramp. This type of float isusually constructed at right angles to the master float. A 144 by 40 foot (44 by 12 m) floating dock, with 10 foot (3
m) wide floats, and 15 foot ( 4.5 m) ramps on both sides can be used for seaplane storage. Additional docks or floats can be added as needed.


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