Gaboon

 Gaboon plywood

A lightweight hardwood used in ply, it has a special significance in boat construction —but also some limitations. Richard Hare and Robertsons BoatyardMike Illingworth explain

Gaboonrole in boatbuilding can be summed up in two words: lightweight plywood. This however should not be misinterpreted as an indictment of its quality; since it helps to reduce a boatdisplacement, ita feature valued in yacht construction, particularly in hulls designed for speed. It gives us a lighter sailing boat.

Otherwise known as okoume (a reflection of its habitat in the former French Equatorial Africa, gaboon (Aucoumea klaineana) is a low-density tropical hardwood (430kg/m3, as opposed to khaya at 530 and utile at 660) available in large diameter logs. This combination makes it excellent for peeling into plywood veneers.

Although indigenous to West Africa, Gaboon plywood arrives in Europe mostly from France and, to a lesser extent, Italy. Greece also produces it. Until quite recently it was also produced in Israel, but log export bans in Gabon meant that Israeli mills have since had to diversify.

Gaboon veneers are now peeled in Gabon for home production (it was only a matter of time). French companies, however, have managed to maintain their own forest concessions and this has enabled them to continue laminating the veneers up into plywood sheets in France. According to Robbins TimberRichard Bagnall, the log export ban and Gabonveneer production under-capacity means that we can expect an imminent price hike of about 5 per cent.

Gaboon has no botanical relation to any of the mahoganies, whether from Africa or the Americas.

Appearance and identification

 Gaboon plywood

With a narrow and clearly defined sapwood, the heartwood when freshly sawn has a salmon-pink colour that tones down on exposure to the atmosphere to a pale reddish brown. It has a medium texture and planes/sands to a silky finish. The grain is slightly interlocked, yielding a very slight stripe figure.

Light weight will immediately alert us to the likelihood of gaboon. On examination of plywood edges weprobably find more laminations (veneers) used in the lay-up than in, say, southeast Asian plywood, this being a fair indication of quality.

Solid samples are not available for us to include a photographic macro image here but, since weonly likely to come across it in plywood form, it would have little relevance. Suffice to say that itdiffuse-porous with medium to large vessels, thin rays and little or no parenchyma.

Where can we view it?

Plywood dinghies, Mirrors being a classic example, are built using gaboon plywood as it keeps weight to a minimum. In modern GRP production yachts it can be used for settee backs and berth bases along with their locker lids, and it will sometimes be used in preference to meranti (CB269) as it has a superior (silky) finish. It will often be used as a substrate for decorative veneered marine-grade plywood (teak-faced being a common example) as its light weight and good working properties favour it for interior fitting out.

Applications

 Gaboon plywood

Gaboon plywood has two distinct roles —dinghy hull construction and ’hulled yacht interior fitting out, these being either GRP or wood/epoxy. Itfar from ideal in clinker and carvel hulls with significantly more water sloshing around in the bilge.

In a yacht, decorative veneered or plain, gaboon plywood is best used above the sole in ventilated parts of a boat (and a boat with unventilated areas is something to be avoided on principle, wood or otherwise).

At Class 4 Natural Durability (’in old money) itonly permitted in BS1088 (marine plywood) for sheets that have to be lightweight. Our use of it should therefore be mindful of this, and it would be tempting fate if we were to use it for, say, a bulkhead that stretches deep into a fetid bilge where itlikely to be wetted routinely with scant opportunity to dry out.

Much the same caution applies to its use in dinghies, and an effective dinghy cover is highly desirable if itto be kept out in the open, typically a damp dinghy park with overhanging trees and long grass. Itworth mentioning that an ineffective dinghy cover —one that allows rain water in, traps it and then goes on to generate a humid hot-house beneath —is worse than no cover at all. Ideally, the cover should try to include a strongback/ridge pole (an oar perhaps?) and a ventilation opening at each end, one that doesnallow rain access. Given this minor precautionary effort, maintenance time will be reduced drastically and more time will be spent on the water.

Gaboon is an easy plywood to work with as it cuts without the breakout and splintering that can occur with meranti.

Whereas most marine-grade plywoods (’use) will be heavier and may well be sold with a 25-year guarantee, gaboon ply (’use) may be sold with a 15-year guarantee. It s worth remembering that these lives are based on high hazard use and the precautions suggested above will extend life indefinitely.

 Gaboon plywood

Although gaboon is best avoided for yacht hull and superstructure construction (25-year guaranteed species should be used here, khaya for example, or quality meranti) it can be used pretty much anywhere else.

Itreasonable to use gaboon ply for cabin construction only when itproperly sealed beneath an effective epoxy/mat laminate and, ideally, a 2-pack polyurethane paint system —and preferably with an outer lamination of ’grade marine plywood.

Varnish and wood finishes

Gaboon takes varnishes and all exterior wood finishes very well but, given the limitations described above, Robertsons’practice is to take particular care to prime ply edges with something that gets in really close and anchors into the end-grain pores. Board surfaces are also given a minimum of two coats of Hempel Woodseal or International UCP before painting.

Alternatively, if the microporous/breathable paint approach is taken below decks, two coats of a a water-based exterior paint like Sadolin Superdec or Dulux Aquatech, while not suitable on ferrous metals, give good results at a very low cost, as in the heads/shower cubicle shown above.

Surface sealing should be omitted (to allow ’), but board edges should still be sealed. Water-based paints don’as oil-based paints tend to.

Regarding varnishing, gaboon can be considered too light in colour for dear-finishing, but heavily pigmented products can overcome this. Always thin first coat.