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Oil Spills and the Marine Environment
navigation. The degree of improvement is a matter of opinion,
and experimental systems have not lived up to some expectations. To
make such a system work, satellites sending out radio waves must
always be within range of the vessel. Electronic devices can
determine the ship location from the radio signals. At the present
time, there are only a limited number of these satellites, so that
position-fixing by satellite is possible for each vessel only at
certain times of each day. More of these satellites would provide a
worldwide network allowing continuous, accurate, essentially
automatic position-fixing.
Collision Avoidance Radar
The
maneuverability of a vessel generally decreases as the vessel size
and weight are increased. Because supertankers are now the largest
vessels on the seas, by their very size they must be relatively
unmaneuverable. Moreover, they are underpowered. To understand
this, one can visualize a 15-foot motorboat weighing 1,500 pounds
operating in calm conditions. If the same relationship between
power and size were applied to this vessel as existed on a 100,000
dwt, one thousand-foot long supertanker having a 20,000 horsepower
engine, the motorboat engine would have only 1/60 of a horsepower.
Complicated maneuvers would be very difficult with so little power.
Much of the economic efficiency of supertankers comes from the fact
that they can transport such large amounts of oil with such small
power plants. Because of their large size and low power, maneuvers
with supertankers take a long time to complete. For example, the
stopping distance for a tanker of 200,000 dwt moving at a forward
speed of sixteen knots with full stern power applied to stop the
ship is about three and a half miles ().
Recent
research has aimed toward the development of collision avoidance
radar systems. Such a system combines a radar set and a computer to
determine the location of nearby ships and obstructions and to
predict the possibility of collisions in advance. The tanker
operator can decide on a possible collision avoidance maneuver and
indicate this to the computer, which will then compute the
trajectory of all vessels, including his own, and show whether the
proposed maneuver will indeed avoid collision. If a collision still
seems possible after the proposed maneuver, the process is repeated
until a safe course is decided upon. Collision avoidance radar
presently exists on eleven ships; the major supplier has orders for
forty-two more units, of which thirty-nine are for oil
tankers.
Harbor
Traffic Control
The problem
of controlling a large number of ships moving inside a harbor can
be ameliorated by a single central traffic control system at the
harbor. Such an arrangement would be similar to today's air traffic
control for airplanes, but there are a number of particular
problems with central harbor traffic control that make it more
difficult than controlling aircraft. For example,