Marine Grade Okoume Plywood:
Never has a construction material been at the center of more confusion about its name, its qualities and its sources. There are three key areas of confusion; the manufacturers and methods; the materials used; and the British Standard specifications & Lloyds of London certifications.
The History of Okoume Marine Grade Plywood:
True marine grade plywood actually dates back to the thirties when Bruynzeel, a door manufacturer in Zaandam, Netherlands, developed a superior form of plywood.
Cornelius (Kees) Bruynzeel was a Dutch businessman, timber merchant and yachtsman. In 1920 he became manager of the family's new door factory in Zaandam. By 1939, their production had expanded to include floors and kitchens, but the threat of World War II was depressing the building industry. Kees began to consider alternative markets and pioneered the development of new timber materials for the production of the Bruynzeel kitchen and for boat construction. Using a newly-developed water-resistant synthetic resin glue, Bruynzeel developed a durable three-ply laminated panel similar to plywood and intended for the fabrication of external doors.
The naval architect Ricus van de Stadt, known to Bruynzeel through the sailing fraternity, received the order to design a daysailer suitable for series production. Bruynzeel suggested that his new “Hechthout” laminated panel, as he called it, was superbly suited as a building material for such a sailing yacht. In 1939 the Valk came into being, still a popular open sailing boat in the Netherlands today. The special marine grade plywood from Bruynzeel was a perfect construction material for the project.
While this established Van de Stadt as an innovative yacht designer, Okoume marine grade plywood from Bruynzeel was also established as the new standard of the industry. Today Bruynzeel Multipanel Int. B.V., as it was later renamed, is a leading timber company that specializes in marine and construction timber.
Bruynzeel now has more than 40 years of experience in the production of marine plywood. Ships built from Bruynzeel that were built over forty years ago are still under sail. This experience enables Bruynzeel to be one of the few plywood manufacturers in the world to offer a 10-year guarantee on its marine plywood.
Bruynzeel used to "own" the US market but as their prices continued to rise, other sources developed. Now this material is largely provided from facilities in Western and Northern Africa (Gabon and Morocco, for example).
The Material—Okoume (Gaboon) Veneers:
The more formal name for this timber is Gaboon, scientific name “Aucoumea klaineana.” You might also see it called “Gabon”, but more commonly, it is simply called “Okoume,” (pronounced, “Oh-koo-mee”). It is also sometimes called “Gaboon Mahogany” or “African Mahogany” though it is not a true mahogany. The trees from which it is derived grow naturally in the West African provinces of Congo and Gabon to heights of over 200 feet.
As woods go, it is not considered a particularly strong wood, nor is it rated good for bending, stiffness or crush strength. But, due to its light weight (average density = 27 lb/ft3, specific gravity = .43) it has an extremely high strength-to-weight ratio.
When rotary cut into veneers and laminated into plywood, it has the appearance of a light-colored mahogany with a very tight, close grain. (see “The Encyclopedia of Wood,” Walker, 2005)
If you are in the United States, unless you have been directly involved in the construction of racing boats or wood aircraft, you more than likely have never heard of this plywood. You may have come across the Douglas fir variety of marine plywood, maybe even some mahogany marine grade plywood but Okoume Marine Grade plywood is something totally different.
Imagine a plywood that has the same core veneers as the faces, and instead of 3 or 5 plies, it has as many 1.5 millimeter plies as it takes to make the desired thickness. Additionally, all the core plies are of the same quality as the face plies—no plugs, no voids. It is also important that any plywood used for boat or aircraft construction be "balanced". A balanced laminate is one in which there is a center ply with an equal number of veneers on either side of it. Additionally, the opposite corresponding veneers must be of the same thicknesses thus making a symmetrical layup.
Okoume Marine Plywood is used for Formula 1 race boats, hydroplanes, canoes, racing dinghies, shells, cabin cruisers, motoryachts, cold-molded boats, lapstrake or clinker-built designs, mine-sweepers or commercial craft. Because of its light weight and high strength to weight ratio, Okoume Marine Plywood is even used in aircraft construction.
Okoume marine grade plywood is made according to a specification. The primary specification is British in its origin and simply called British Standard 1088 or “BS-1088.”
The plies are bonded with WBP (water and boil proof) phenolic glue (often called resorcinol). The BS-1088 plywood must use an adhesive proven to be very resistant to weather, micro-organisms, cold and boiling water, steam and dry heat. The product's adhesive bond must pass a series of British Standard tests.
The face veneers must present a solid surface that is free from open defects. Face veneers must be free of knots other than "sound pin" knots, and there can be no more than an average of two such knots per square foot over the entire surface of the plywood sheet. The veneers must be reasonably free from irregular grain. The use of edge joints is limited, and end joints are not allowed.
The core veneers have the same basic requirements as face veneers, except that small splits are allowed, and there is no limit on the number of pin knots or edge joints. However, end joints are still not permitted.
Defective bonds, pleats and overlaps, and gaps in faces are not permitted. Occasional gaps may be repaired using veneer inserts bonded with the proper adhesive.
Moisture Content -- BS 1088 plywood must have a moisture content between 6% and 14% when it leaves the factory.
It is important to note that there is a sister specification, BS-6566, for a lesser grade panel with thinner face veneers of lower quality, and fewer laminations.
The big difference here is between a plywood panel being manufactured to comply with the BS-1088 specification and one that is actually certified that it complies.
Lloyds of London, the famous insurance company, provides a certification for these plywoods for use in yachts. Okoume lumber, as a species is rated as a non-durable wood. In order to obtain a rating by Lloyds as equivalent to a minimum of moderately durable, Okoume plywood must be treated with a preservative. Because of this treatment Lloyds Register provides an approval for applications in pleasure craft and small craft construction. There are several manufacturers of Okoume plywood but not all have this rating.
Today’s Supply Chain:
As with many manufacturers, reputation supports a brand name along with rising prices. Such is the case with Bruynzeel. In the last few years, their prices have risen so sharply that a market void was created, encouraging competition to new players.
Since most of the Okoume timber comes from Western Africa, it was only logical that a manufacturing plant would develop there.
The Joubert Group:
One of the most recent players in the production of this certified plywood is the Joubert Group, based in France. In 2000, Joubert completed their veneer peeling and drying plant in the equatorial Western African seacoast town of Port Gentil, Gabon. Joubert produces two marine grades; their “Joubert Marine Ply” and their “Super Marine Ply” okoume plywoods to meet the BS-1088 standards with the main difference between the two being the number of plies.
The company, CEMA, Bois De L’Atlas, located in the city of Casablanca, Morocco, in the northwestern portion of Africa has been making BS-1088 certified Okoume plywood for several years now.