Polyethylene Vs. Fiberglass Boat
Different Materials, Different Technique
Polyethylene hulls are "thermoplastic" hulls. This means that plastic pellets are injected into two molds that are in the shape of the boat. One is slightly smaller than the other, because one forms the boat's inner surface and the other forms the boat's outer skin. The pellets are heated and melt to fill the molds. A layer of flotation material is then sandwiched between the outer skin and the boat's inner surface to meet Coast Guard requirements.
A fiberglass boat is molded, too, but the mold only defines the outer skin of the boat. The fiberglass material and resin is hand-laid over the mold and, when the resin has fully cured, the mold is removed from the outside of the fiberglass hull.
Thermoplastic molding allows a polyethylene boat factory to produce 1,400 or more hulls per week. This high level of production means that polyethylene boats are available at large retail stores. A fiberglass boat builder may produce between five and 10 hulls each week, for sale in dedicated distributorships. Economy of scale and access to a wider distribution network ensures that the polyethylene boat manufacturer's cost-per-boat is significantly lower than the cost-per-boat for fiberglass boats, and this means a drastic price difference between the two hull types.
Polyethylene hulls are heavy when compared to a fiberglass hull the same size. High-density polyethylene weights 5.04 pounds per cubic foot. The urethane foam used for flotation material -- the lightest weight compliant with federal regulations -- weighs 2 pounds per cubic foot, for a total of 7.04 pounds per cubic foot. Fiberglass weighs 2 pounds per cubic foot and requires an equal weight of resin, for a total of 4.0 pounds per cubic foot.
Polyethylene boats lack stringers and hull frames -- the equivalent of rafters, joists and studs in building construction -- that give a fiberglass hull stiffness and strength. This limits the length and width of polyethylene boats. Fiberglass, on the other hand, is used in yachts of 150 feet or more in length. In the end, you get what you pay for.
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