MIL-HDBK-1025/5
Flotation Materials
2.3.4.2
Timber Log. Although least expensive in some areas, it has a
a)
tendency to become waterlogged and sink in a few years. Use is generally not
recommended.
Extruded Polystyrene (Styrofoam). Available in several sizes
b)
of precast or premolded forms, mounted under a timber frame with timber deck.
Expanded-Pellet Polystyrene. Material shall be firm in
c)
composition and essentially unicellular. Polystyrene planks should conform to
the following requirements:
1) Be hydrocarbon resistant, and evidence no apparent
softening or swelling when tested by the immersion method stipulated in
Military Specification MIL-P-40619, Plastic Material, Cellular, Polystyrene
(For Buoyancy Applications).
2) Minimum Properties. Density = l-1/2 pounds/cu. ft.
Compressive strength = 20 pounds/cu. in. at 5 percent deflection. Shear
strength - 25 pounds psi and 40 psi tensile strength.
3) Have maximum water absorption of 0.12 psf of skinless or
rindless surface, when tested by the immersion method stipulated in Military
Specification MIL-P-40619.
Polyurethane Foam. This is more expensive than pellet
d)
polystyrene; however, it is sometimes preferred because of its hydrocarbon
resistance. Polyurethane foam requires a covering with an oxidation-resistant
material; the nonabsorbent, noncellular variety should be specified.
Waterproof Shells. Shell-type floats can be ballasted with
e)
water or sand to allow corrective leveling of the deck after installation.
However, they are susceptible to leakage and loss of buoyancy if the shell
becomes permeable for any reason. Some of the shell-type floats in use are:
1) Fiberglass of plastic-coated shell with a molded foam core
over which a reinforced concrete deck is poured. The edge beam, cross beam,
and the tie-rod system in this construction make the units exceptionally tough
and strong. Synthetic shell floats are not affected by hydrocarbons, brackish
water, or any other common contaminant likely to be found in a small craft
harbor.
2) Prefabricated metal floats of steel and aluminum. The
shells are folded and welded into rectangular units comprising thin-gauge
sheets with stiffening baffles for greater strengths. Preservative coatings
are applied to both sides of all corrodible metals. Their use in freshwater
harbor basins is feasible, but in saltwater environment the use of metal
floats still remains questionable.
3) Jettisoned fuel tanks from military aircraft.
This type
is expedient when sufficient surplus can be procured at low cost.
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