Environmental Engineering Reference
In-Depth Information
century. For the wood requirements of some of the earliest seafaring vessels we have
Homer's description of Odysseus building his boat (the shipbuilding passage in the
Odyssey
5:23-253): “Twenty trees in all did he fell, and trimmed them with the axe;
then he cunningly smoothed them all and made them straight to the line.”
Assuming, rather generously, 1.5 m
3
of wood per tree puts the upper limit of
timber required to build that mythical Bronze Age ship at about 30 m
3
; with wood
waste at no less than 30% and an air-dried weight of no more than 600 kg/m
3
, the
actual volume of the ship timber would be just over 20 m
3
and its mass would be
about 12 t. Much larger ships (such as those for transporting Egyptian obelisks to
Rome) were built in antiquity, but their voyages were limited to coastal and cross-
Mediterranean trafi c. The i rst long-distance voyages by Europeans were done by
the Vikings, who used their elegant long ships to roam the North Atlantic (all the
way to North America), the Mediterranean, and the Black Sea.
A well-preserved Gokstad ship (built around 890 CE and discovered in Norway
in 1880) displaced 20 t, and its construction (including the mast and 16 pairs of
oars) required the wood of 74 oaks. The ships that made the i rst long-distance
voyages from Europe half a millennium later were still fairly small: Vasco da
Gama's
São Gabriel
(it reached India in 1498) displaced only about 80 t, Magel-
lan's
Victoria
was only marginally larger, at 85 t, and Columbus's
Santa María
displaced about 110 t. With hulls, masts, and spars accounting for 65%-70% of
the total displacement (the rest being sails, ballast, supplies, armaments, and crew),
those ships contained between 50 and 75 t of sawn timber (Fernández-González
2006). Wooden ships reached record sizes, and several European navies built them
in record numbers, during the last century before the introduction of steam pro-
pulsion (the i rst oceangoing steamer came during the 1830s), and the volumes of
timber delivered to shipyards substantially surpassed the timber incorporated into
new vessels (box 9.4).
Shipbuilding claims expressed in terms of actual forest harvests depended on the
species and the density and maturity of the exploited stands. The maximum density
for the best shipbuilding timber—fully mature (after some 100 years of growth)
British oaks—was about 100 trees/ha, and with every such tree yielding 2.8 m
3
(two loads) of wood, the cut amounted to 280 m
3
, or about 200 t/ha. A slightly
denser but immature stand yielded only one load per tree, or about 120 t/ha. Build-
ing a ship containing 4,000 t of wood (requiring about 6,000 t of delivered timber)
thus claimed anywhere between 30 and 50 ha. That much wood would have sufi ced
to provide an annual supply of fuel for as many as 1,500 families—but the com-
parison is revealing only in strictly quantitative terms, as any woody phytomass can
