Plastics Make Waves in Marine Applications

With its new 225-hp, six-cylinder Verado engine, Mercury Marine has taken the use of plastics to a whole new level in engineering design.

The engine sports a sculpted, multi-piece cowling assembly that features the world's largest injection-molded nylon cosmetic part. The cowling meets stringent structural requirements at a lower weight than conventional one-piece bucket-like engine covers made from sheet molding compound or thermoformed sheet-and costs less too.

The assembly consists of three injection-molded plastic cowls: The 33.5 x 22.9 x 16.4-inch top is made from a 33% glass-filled nylon 66 and weighs 11.3 lbs. DuPont Engineering says it's the largest injection-molded cosmetic nylon part in the world. A structural real cowl made from the same nylon mates with the top cowl and attaches to an aluminum structural member that itself attaches the engine to the boat. A smaller front cowl molded from two pieces of glass- and mineral-filled Minlon nylon completes the upper-engine housing.

Among engineering advantages of the design is weight reduction. The cowling assembly weighs 30% less than sheet molding compound. Part of the weight savings comes from the thermoplastic's specific gravity advantage vs sheet molding compound. Additionally, while sheet molding compound often requires bulked-up regions for proper molding, the plastic parts have relatively thin nominal wall thicknesses. The injection-molded parts also allow molded-in features that would be impossible with a compression-molded part. The cowling's patented integrated latching system is a case in point. It integrates what were separate hinge-mounting points, cable guides, and brackets right into the top cowl. Result: elimination of bolted-on latches.