WHOI-90-52

of the inherent limitations of radar. The rage of rada is limite to the horizon, and visibilty
ca be obscured by topography and structures. Even using towers of maximum height, it would
require a great number of them to cover the essential navigable waters -- and then adequate
coverage couldn't be guarantee. Clealy, a better approach to the problem is neeed.
The Port and Tanker Safety Act requires the following navigation equipment on board all vessels
of 10,00 or more gross tons:
.
.
. .
a dual radar system
an ARPA (automatic radar plotting aid to IMO speifications)
an electronic position fixing device
adequate communications equipment
a sonic depth-finder
a gyrocompass
up-to-date chars
All of the equipment and systems available to meet these seven requirements have been improved
since 1978. Position fixing by LORAN-C and GPS and communications by INARSA T have
improved most dramaticaly in both performance and in reduce cost. Improvement in charng
wil also ocur as electronic char data is employed in conjunction with the data from other
equipment to enhance the safety and accuracy of on-board navigation.
One concet of a system to accomplish comprehensive shore-base monitoring of all taers and
other hazdous liquid cago caers is base on the mandatory reportng of position of all such
vessels in U.S. waters. The reporting of position ca be made manualy or it ca be automate
by a device connected to a LORAN-C and/or GPS reciver(s). This makes it possible to
periodicaly collect and format position data (and possibly data from other sensors) for
transmission via INARSAT'S low-cost Stadad-C service to ground-base facilties where the
data would be procsse automaticay. Possibly as few as two such facilties locte one on
each coast could handle the traffic. The position reports would be monitored by a computer
relative to defined permissible navigation areas. Any vessels out of, or approaching the limits
of, these areas would then be flagged for manual interrogation via an INARSAT Stadad-A
voice channeL.
Such a position reportng system does not eliminate the nee for radar base VTS' for harbors.
At short range, radar determines position relative to shorelines, buoys and strctures more
accurately than does LORAN-C or GPS. Furtermore, rada images accurately superimpose
on electronic chars show position of traffc relative to depth contours, underwater hazds, and
the boundares of navigation channels.
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