Environmental Engineering Reference
In-Depth Information
Consequently, the most efficient position requires the
rider to put his center of gravity not only forward but
low (K. S. Thomson 1987). The jockey's crouch is the
best way, but skillful riders have used other postures
that also allowed them to discharge weapons in gallop
(Clutton-Brock 1992). Classical riders were even more
disadvantaged because they did not have the stabilizing
stirrups that spread westward through Eurasia after the
third century. Good riders had no difficulty doing 50-
60 km/day on a fit animal on a passable road, and with
horse changes they could cover well over 100 km/day in
emergencies.
Much higher record claims were made for the Mongo-
lian yam (message delivery) service (Marshall 1993), and
in 1860 William F. Cody's legendary ride covered 515
km in 21 hours and 40 minutes (R. A. Carter 2000).
But typical performances were carefully optimized. Mine-
tti (2003) concluded that relay postal systems based their
selection of average speed (13-16 km/h) and daily dis-
tance (18-25 km) covered by an animal on minimizing
the risk of damage to the horses, avoiding the emptying
of spleen and anaerobic metabolism and allowing for
adequate cooling. Remarkably, this optimal choice ap-
plied equally well to the ancient Persian service set up be-
tween Susa and Sardis by Cyrus after 550
B
.
C
.
E
., which
Xenophon called ''undeniably the fastest travel by land
possible by humans''; to messengers in the far-flung
Mongol Empire of the thirteenth century; and to the fa-
mous Overland Pony Express of 1860, which reached
California before the telegraph and the railway.
Compared to the flows of 100-1000 W that domi-
nated the energy inputs in animate land transport,
human-powered waterborne movement operated at
much higher rates. Oared vessels offered some spectacu-
lar examples of clever design and mass labor integration
albeit often terrible suffering of crews chained to the
oars of large galleys (Morrison and Williams 1968;
Hocker and Ward 2004). Assuming 80% rowing effi-
ciency and useful power between 100 W (sustainable for
hours) and 200 W (shorter bursts), the 50-rower pente-
conteres that took the Greek troops to Troy were pro-
pelled with 3.5-7 kW. Triple-tiered Greek and Roman
triremes were probably the best-performing classical war-
ships. Their seating of 170 rowers has been a perpetual
puzzle for naval historians. Their 24-kW power was
enough to propel the ship over 20 km/h into a devastat-
ing ramming attack. Equipped with bronze rams, these
ships made it possible for a smaller Greek force to defeat
a large Persian fleet at Salamis in 480
B
.
C
.
E
., and later
they became the most important warships of republican
Rome. Their successful full-scale reconstruction was fi-
nally accomplished during the 1980s (Morrison, Coates,
and Rankov 2000).
The sequence of larger oared ships ended with a fail-
ure: a 128-m-long tessarakonter, built in the Ptolemaic
Egypt (210
B
.
C
.
E
.). This vessel, designed to carry more
than 4,000 oarsmen and nearly 3,000 troops and to be
propelled with over 5 MW of muscle power, proved too
heavy to use. Large European oared vessels remained in
use until the seventeenth century, when some Venetian
galleys had 56 oars, each crewed by five men (Lane
1934). Large Maori dugout canoes were rowed by al-
most as many warriors (up to 200), indicating a universal
limit of 12-20 kW for aggregate human power in sus-
tained rowing applications. In addition to oared ships
there were vessels powered by pedaling or stepping on
treadmills. The Sung dynasty Chinese built paddle-wheel
warships powered by up to 200 men, and in Europe
tugs powered by 40 men turning capstans or treadmills
appeared after 1550 (Needham 1965).
