BOATBUILDING WITH PLYWOOD, by Glen L. Witt

CHAPTER 5 - LUMBER

Hardwoods

LUMBER SPECIES FOR BOAT BUILDING

While there are probably thousands of different wood species throughout the world, most of them are not suitable for boat building. Many woods are unsuitable for at least one of a variety of reasons. They may be too weak, too brittle, too soft, subject to decay, will not hold fastenings well, or the trees may be too short to yield lengths of material suitable for boat building. In the following descriptions, those woods which have been proven in use in boat building over a period of literally generations in the United States are noted, as well as some which may be of only limited value or which are unsuitable, but are often confused with similar suitable types. Even though many types are imported, they are often readily available. The nomenclature of the various woods given is the commercial name. Where the wood may be known under other names, these have been listed in parentheses. Weights of each wood are given per cubic foot and per board foot at 15% moisture content on an average basis. Variations in weights, however, will occur in a given species due to variations in moisture content, heartwood to sapwood ratio, and other factors. For practical purposes a wood that weighs under 2.5 lbs. per board foot is considered light in weight. A wood that exceeds about 3.3 lbs. per board foot is considered heavy. Woods that weigh between these figures are considered medium weight woods. The descriptions are broken down into the two categories; hardwoods and softwoods. Because of their special qualities and limited uses, not all the woods listed are applicable to boat building with plywood; but they are noted since they are often sold in lumberyards specializing in boat building woods.

HARDWOODS

APITONG
44 lbs. per cubic foot, 3.67 lbs. per board foot.
Abundant in the Philippines, Indonesia, Malaysia, and New Guinea, There are many different species, however, they look very much alike. Sapwood is creamy yellow, gray, or reddish white, while heartwood is reddish purple or brown. The grain is usually straight. The wood is slow to dry, does not take preservatives too well, is moderately low in decay resistance, and somewhat difficult to work. Apitong is very hard, strong, holds fastenings very well, and is often substituted for white oak but it is not nearly as durable.

ASH, WHITE
42 lbs. per cubic foot, 3.5 lbs. per board foot.
A domestic wood grown mainly in the Eastern states. The heartwood is brown, while the sapwood is light in color or nearly white. The wood is hard, fairly strong, straight grained, and suitable for steam bending. It can be substituted for white oak in areas that will not be continually moist. Decay resistance is low. Often used for small boat framing, oars, tillers, and joinerywork.

ELM, ROCK
44 lbs. per cubic foot, 3.67 lbs. per board foot
A domestic wood that grows in the North Central and Northern states. It has only limited use in boat building, mainly because it is suitable for steam bending. The wood is hard, strong, and shock resistant, which makes it suited well for small boats utilizing steam bent frames and laminated members. Decay resistance is fair at best and the wood tends to warp.

GREENHEART
61 lbs. per cubic foot, 5.08 lbs. per board foot
The wood is native to South America and the West Indies, however, it is imported mostly from Guiana. The heartwood is extremely decay resistant and has a reputation for being highly resistant to marine borers that may not be completely deserved when used in tropical waters. The wood was once a favorite with European builders since it is stiff and very strong. Its color varies from pale greenish-yellow to deep brownish purple, with little difference between sapwood and heartwood. The high weight can be a considerable disadvantage in some designs. Being a very hard, dense wood, it can be more difficult to work than other hardwoods.

IROKO
40 lbs. per cubic foot, 3.33 lbs. per board foot
The tree comes from tropical Africa and is much like teak, but not as strong. The heartwood is decay resistant and somewhat resistant to marine borers. The wood is hard, but moderately easy to work. Heartwood is light to greenish yellow, but darkens to brown upon exposure to light and air. Iroko is very popular for boat building in Europe.

IRONBARK
(eucalyptus)
62 lbs. per cubic foot, 5.17 lbs. per board foot
Several species of Eucalyptus called red and gray ironbark are native to Australia where they are most used. Heartwood is red to dark brown, and sapwood is light colored. The heartwood has good decay resistance, and is resistant to some forms of marine borers. The wood is very hard, heavy, strong, and shrinks moderately. Because of its high weight, the wood can be a major disadvantage in many types of boats.

LIGNUMVITAE
(ironwood)
76 lbs. per cubic foot, 6.33 lbs. per board foot
One of the hardest and heaviest woods known, it is found in Central America and the West Indies. The wood is naturally impregnated with oils which makes it suitable for propeller and rudder shaft bearings (its major function) as long as shaft RPM is not too high. Heartwood varies from olive brown or blue to dark brown or nearly black, while sapwood is cream colored. The heartwood is very resistant to decay and abrasion. The wood is often used for keel and worm shoes, rubbing strakes, etc. It is extremely strong with regard to crushing and hardness.

MAHOGANY, AFRICAN
(khaya, utile)
32 lbs. per cubic foot, 2.67 lbs. per board foot
Very similar to genuine mahogany, it comes from Africa. Color ranges from light pink to bright red or reddish brown, but is not as variable as mahogany. The wood is hard, strong, decay resistant, of low shrinkage, and seasons well. There are several species of so-called "African" mahoganies, but those listed above are the most suitable for boat building.

MAHOGANY, HONDURAS
(Mexican mahogany)
34 lbs. per cubic foot, 2.83 lbs. per board foot
True mahogany grows in the West Indies, Central America, the northern part of South America, and some in the southern part of Florida. The types frequently used in boating are called Honduras and Mexican mahoganies. Color varies from deep red to reddish brown in the heartwood, with sapwood a pale yellow. The heartwood is decay resistant, fairly strong, and seasons well, with low and uniform shrinkage. Hardness, weight, and strength can vary depending on where the lumber is from, with the Central American variety being more variable.

MAHOGANY, PHILIPPINE
(tangile, red luan, white luan, tiaong)
39 lbs. per cubic foot, 3.25 lbs. per board foot
The many varieties of so-called "Philippine mahogany" are really types of tropical cedar common to the Philippines even though they resemble true mahogany. The dark red varieties are harder, heavier, more decay resistant, and stronger than the light red varieties that are usually limited to nonstructural joinerywork. The trees yield large, clear boards, although interlocked grain can make seasoning some times difficult.

OAK, WHITE
47 lbs. per cubic foot, 3.83 lbs. per board foot
White oak is a domestic Eastern wood often used in boat building. The problem with white oak, however, is distinguishing it from red oak that is not nearly as suitable for boat building since it is weaker and rots easily unless pressure treated with preservatives. The following characteristics should help in separating white oak from red oak. The heartwood pores will be plugged with abundant hair-like ingrowths known as tyloses, whereas red oak will contain few. The heartwood of white oak is tan or light brown, while that of red oak is reddish or pink. The pores in summer wood are very small and numerous in white oak, but with red oak they are few, large, and open. A chemical test using benzidine-sodium nitrate turns white oak heartwood dark brown or greenish brown, but that of red oak turns light orange. White oak is excellent for steam bending but should ideally be "green" for this purpose and not seasoned. It is durable, stiff, strong, hard, holds fastenings very well, is rot resistant, but is somewhat difficult to work and requires sharp tools. Because of the gallic acid in white oak, it reacts with plastic resin glue when submerged in salt water, and therefore this glue should not be used with white oak under these conditions.

OKOUME
(gaboon)
27 lbs. per cubic foot, 2.08 lbs. per board foot.
This West African wood produces large, clear logs of uniform straight grain. The heartwood is salmon pink or pale pinkish brown resembling some types of Philippine mahogany. The sapwood is grayish. It is only fairly strong considering other woods, but strong for its weight, although low in resistance to decay. The wood splinters easily and is best sawn with carbide tipped blades. It has little use in plywood boat building except in smaller boats where lightweight is more important than durability. Some imported plywood is made from this wood.

TEAK
43 lbs. per cubic foot, 3.58 lbs. per board foot
Probably the most decay resistant wood in the world, but it is not totally immune to marine borer attack. The wood grows in Burma, India, Thailand, and the East Indies. Sapwood is white to pale yellowish brown, while heartwood is a dark golden yellow that darkens with age. The wood has a rough oily feel, is straight grained and coarse, strong, hard, of low shrinkage, and easily worked but brittle, and tends to dull tools. Very commonly used for decking, joinerywork, and frequently left unfinished, it is a very durable wood. Glues used with this wood must be selected with care.

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