Choosing Wood for Marine Applications

In an age of plastics and composites, wood has not surrendered its claim on the mariner. The color and texture of grain, the particular warmth of wood in the sun, the way a teak gunwale is shaped precisely to meet the grasping hand: these qualities of wood embody the romance of the sea. But unlike our nautical forebears, who were intimately acquainted with the properties of spruce and cedar and teak and jarrah, many mariners of today are not familiar with the proper means of selecting woods for marine use. In this two-part series, we’ll explore a straightforward procedure for choosing, installing, and finishing wood. In this issue, we’ll begin on the boat, with the challenge of wood selection.

Understanding the application

Before repairing or replacing wood on your boat, it is crucial to know the structural role the wood will play. Exterior marine surfaces such as decks,gunwales and hardware mounts are fashioned from dense, decay-resistant woods like teak and white oak. Teak has long been popular for its strength and durability. The British Admiralty pilot books still warn cargo ships to avoid colliding with Asian teak-hulled junks, as the wood often prevails against steel hull plates. The wood’s natural oils provide outstanding resistance to moisture, and it can be left unfinished without compromising its longevity. The teak of the cave temples in Salsette, India, is two thousand years old and perfectly intact.

While teak is ubiquitous, many other seafaring woods are equally strong and durable: greenheart, jarrah, African blackwood. Shackleton’s Endurance was sheathed in greenheart, and the railway ties of the London Underground are of jarrah. Lignum vitae, the toughest commercially-available wood, far exceeds teak in density, strength, stiffness, and decay resistance. North American suppliers seldom carry these more exotic hardwoods in quantity, though they will often stock small boards or blanks used by woodturners.

In general, tougher is better, especially for hardware mounts. Thankfully, most dense woods are also highly moisture resistant. And their natural oils produce a dark, lustrous sheen that is quite beautiful. But they are expensive, and therefore unsuitable for large projects such as decks and gunwales. Teak, oak and mahogany, though also pricey (but less so), can be found in large quantities in most metropolitan areas. Be cautious in choosing mahogany: since 1595, when the carpenter on Sir Walter Raleigh’s ship first discovered its properties and introduced them to European craftsmen, mahogany has been the unfortunate victim of colossal over-harvesting. The Honduras and Cuban varieties are endangered, and today many types of ‘mahogany’ are in fact inferior substitutes like agba, ramin, and Philippine mahogany (also called lauan, and not a true mahogany).

Many woods from the rain forests of the Pacific Northwest also make excellent seafaring woods in specific applications. Douglas Fir is stronger than steel (by weight), and it is light, stiff, and easy to work. Maple is durable and flexible. Western red cedar is wonderfully resistant to decay. These woods are plentiful and relatively inexpensive, though they typically require care in finishing and, except for maple, are unsuitable in situations where mechanical strength is required.

Before you visit the lumberyard or wood shop, decide whether you need a light wood (such as for spars, oars and dinghy parts), or a dense, heavy wood(for hardware mountings and other fittings). Don’t worry about whether you need a‘hardwood’ or a ‘softwood.’ These terms, which denote structural differences among trees and don’t actually describe hardness and softness, can be misleading: balsa is a hardwood.

Knowing Your Wood

If you decide to replace wood on your boat with the same species, to match grain and color, don’t assume the wood is teak (or oak). Iroko and Rhodesian teak – not a true teak but a much tougher wood – are two common teak substitutes. Similarly, spruce, pine, and fir are frequently graded as equivalent in the Pacific Northwest: the letters SPF are stamped on lumber to assign this aggregate designation. Moreover, within each wood species there is a great variety in color and grain. If you’re replacing an existing marine fixture, plan on taking a sample of your old wood with you to the wood shop. Scrape off the finish and the first few layers of decayed and sun-darkened wood to get a clear picture of the wood’s true character. Odd as it may sound, put your nose to the wood and smell it. Take a deep whiff and try to remember the scent; this is sometimes the best guide in matching wood species. If you’re not sure what kind of wood you have, and you want to be definitive in naming it, head down to the library and consult R. Bruce Hoadley’s Identifying Wood: Accurate Results with Simple Tools.

Selecting Lumber

Find a reputable wood supplier; it’s essential to good craftsmanship. Ask around at marinas or visit wood shows and specialty stores. Hardware megastores usually carry only a few wood species such as oak and pine and fir, and much of the wood is damp. You won’t find teak. Instead, look for a supplier who deals in kiln-dried hardwood and woodworking tools. These outfits are typically well-staffed and well-stocked.

If you’re undertaking several wood projects on your boat, invest in a moisture meter (available from specialty shops for about a hundred dollars). The science of wood decay is inordinately complex, but much of it comes down to a single factor: moisture content. Some shops guarantee moisture levels below the critical threshold of about eighteen percent, but frequently there’s no way to tell except by testing. Ask the shop staff about their policy. And make sure you have a sharp knife and a tape measure on hand; you’ll need them.

Many wood suppliers have stacks of wood outside. No matter how enticing these look, avoid them. Wood stored outside is wet, and finding dry wood is your most pressing concern. This holds true even if you won’t be finishing the wood, and it will be exposed to moisture year round. Wet wood is difficult to work,is prone to decay, and will shrink over time. You don’t want your deck plank to be a quarter inch narrower next year. Find wood that is stored in a heated, insulated building.

When you come across a stack of the wood species you’re looking for, take as many boards as you can manage off the stack and line them up vertically. Naturally, the best boards are always at the back or bottom of the stack. (Make sure you re-stack the boards neatly when you’re done; most shops post signs to this effect in prominent locations.)

Check the moisture content. If the wood feels or smells damp, move on. Dry wood tends to be rough and splintery on the surface, whereas wet wood fibers feel smooth to the touch. In place of a moisture meter, this shorthand might help, but be aware that wood dries from the outside in, and dryness on the exterior by no means guarantees dryness throughout.

Smell the wood. Make sure it has the same scent as the existing wood on your boat. Now, taking each board in turn, lay it flat or, if the board is small, hold it in front of you at eye level. Look at the orientation of the grain lines at the board’s end. Try to find grain lines that run vertically or at a slight angle. As you stand with the board laid or held flat, the grain lines should point roughly toward the ceiling. You may also notice these lines continuing on the face of the board. This quartersawn orientation, sometimes called vertical grain, is an essential feature of stable wood. Next, look for bending and warping along the length of the board. Don’t imagine you can remove cupping or bowing when you install the piece; usually, you can’t.

Find twice as many flat, straight, and quartersawn planks as you need. Put everything else back. Arrange the finalists in a row and look for cracks and knots. Inspect all four sides of each piece. Look for dark bands of moisture or abrupt changes in color. Narrow the finalists down by looking for what woodworkers call figure: texture and sweep in the grain, richness of color, aesthetics. Use your knife to scrape away a few layers of wood to make sure the color is consistent, not simply a function of recent sunlight exposure.

Make your final selection, and make sure you choose more wood than you need; wood projects always require extra material (I typically purchase twenty percent more than the measurements call for). Measure the final pieces. Make sure their dimensions exceed the measurements from the boat (which, of course, you’ve brought with you on a slip of paper). Stack the pieces on your shoulder and head for the cashier.