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Boats
Transportation
by water has been present throughout history. The density
of people is about the same as that of water and this permits easy swimming
or floating. Simple rafts or boats of the types shown in the diagram permit
the utilization of waterways for transporting loads over long distances with
little energy expenditure compared to travel by land. The boats shown utilize
Archimedies princple to float. They may be constructed from low density materials
(rafts) or hollow section that displace the needed quantity of water.
At
low speeds the resistance to motion through still water is low, but
it increases as the square of the relative speed between the boat and the water.
If the structure of the boat or the load being carried extends considerably
above the water surface, wind resistance will also have to be overcome. |
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From:
Abbott, Brooks and Wilson, Human-Powered Watercraft, in "Human-Powered
Vehicles," Human Kinetics (1995) |
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