Non-Traditional Boat Building Materials

Jerry Culik takes a deep dive into some less common construction materials

Wood, plywood, epoxy, and glass fabric have been standard small boat building materials for decades. Today premium fabrics of Kevlar or carbon fibers might substitute for glass to provide high strength and lighter weight. They look good, too. While Plexiglass, Lexan, and “Starboard” are the most common sheet plastics found on boats, here are several more lesser-known materials that have good potential as boat building materials. And before you dismiss them out of hand, be sure to consider the time and material costs required to finish and to preserve many of the traditional boat building materials.

Epoxy-glass and Carbon Fiber Composites

G-10/FR4 (aka, “Garolite”) is a glass-epoxy laminate cured at high pressure and temperature to produce sheets with high strength, low moisture absorption, and high chemical resistance. GPO-3 has similar characteristics, uses a polyester resin, and is lower cost; G-10 is an epoxy laminate. Since G-10 is an excellent electrical insulator, its most common use is in electrical and electronic applications, especially at high voltages. However, its mechanical strength and waterproof properties make it incredibly useful in the marine environment.

G-10 is produced in sheets up to 2” thick and is also available as tubes and rods. It’s not cheap stuff. A large sheet of ¼” thick G-10 costs around $25-30/sq-ft; and a small 12”x12” piece will run about $60 from Professional Plastics or McMaster-Carr. It’s an excellent choice for high-stress applications where you might also choose stainless steel or aluminum. As a backing plate, the information I’ve found suggests that there’s a stiffness/strength equivalence between 3/16” thick stainless steel, ¼” aluminum, and ⅜” to ½” thick G-10 sheet.

For a given area and using those thicknesses, a G-10 and an aluminum backing plate would weigh about half that of a stainless steel plate, and of course G-10 and aluminum are much easier to cut and drill than stainless steel. Additionally, G-10 will not corrode like aluminum if saltwater breaches the fixture’s bedding compound (for details on replacing or installing backing plates, see Capt’n Paul Esterle’s article in Small Craft Advisor #86, Mar/Apr 2014). G-10 does have one potential downside besides cost: since epoxy is sensitive to UV, it’s best to coat or paint G-10 board if used outside and you’re not sure that it has a “built-in” UV inhibitor.

Weight, in pounds per square foot, is critical for boatbuilding because it impacts the useful load—displacement minus the constructed weight—of any given hull. Plywood, particularly okoume plywood, is a very lightweight boat building material. A 4’ x 8’ sheet of 6-mm (¼”) okoume sheet weighs 21 lbs; and 12-mm is double that. Laminating 6-oz fiberglass (6 oz/sq-yd x 3.6 sq-yd for a sheet of plywood = 22 oz) and epoxy to fill the weave (with another 22 oz of epoxy for a 50:50 resin-to-glass fill ratio, per “Gougeon Brothers on Boat Building,” pg. 126) on both sides will add about 3 pounds per side. “Flocoating” plywood (with no glass fiber) for sealing the surface typically adds about 2 pounds (32 oz) of epoxy per sheet, per side (“Gougeon Brothers on Boat Building,” pg. 156). As a baseline for comparison to other materials, the weight of a 6-mm sheet increases to 25-27 lbs, or 0.8 lb/sq-ft. And figure on 1.5 lb/sq-ft for coated and glassed 12-mm okoume.