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APPENDIX
G
A Primer on Navigation Technologies
This appendix provides basic descriptions of navigation technologies and
serves as background material for Chapter 6. The first section outlines traditional
bridge design and operation, noting the physical location of the various technol-
ogies. It provides a baseline from which to evaluate the advantages of the inte-
grated bridge and integrated ship-control systems. The remainder of the appen-
dix lists technologies in alphabetical order, briefly noting their important features
and uses with particular reference to issues addressed in Chapter 6. Off-ship
navigation technologies and essential navigation publications are included.
The descriptions are not comprehensive; there are a multitude of possible
designs, uses, and combinations of many navigation technologies. These varia-
tions are due in part to the changeable marine environment. For example, radar is
used for collision avoidance at sea. On approach to or while operating in pilotage
waters, radar is also used to determine own ship positions.
TRADITIONAL BRIDGE DESIGN AND OPERATION
Functionally, the traditional bridge-that seen on most ships today is laid
out to support a method of operations that has not changed much since the days
of sailing ships. Equipment and instrumentation are scattered about the bridge
based on where the various members of the bridge team would be expected to
stand during specific navigation or piloting functions. No area is equipped to
support, by itself, the complete operation. Steering is controlled from the hub of
the bridge based on orders from the watch officer, who may be at either side of
the bridge observing radar or anywhere on the bridge or bridge wings during
. ~ .
piloting.
434
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A PRIMER ON NAVIGATION TECHNOLOGIES
435
The traditional navigation bridge has evolved from that of sailing ships,
without much change in spatial arrangement or work functions. The bridge is
located above the crew accommodations, which usually are aft on modern tank-
ers, bulk carriers, and container ships and forward on ferries, cruise ships, war-
ships, and most car carriers.
On sailing ships, the bridge was aft, a position dictated by the location of the
rudder. Until the advent of the steering engine, rudders were controlled by tillers
or an arrangement of ropes and blocks and manpower. Thus, navigation and
steering equipment had to be near the rudder. When steering engines and re-
mote-control devices became available, the accommodations and bridge moved
forward to amidships on early tankers, to provide more visibility forward of the
bow. This, unfortunately, placed some accommodations directly over the cargo
tanks. After many fires that led to loss of life among crews in midship houses,
the International Convention for the Safety of Life at Sea (1974' and its 1978
Protocol (SOLAS) mandated that accommodations on tankers be located aft of
the cargo block.
This change protected the crew from cargo fires, but the price was loss of
visibility from the bridge. A large part of the sea immediately in front of the bow
cannot be seen. On containerships with similar superstructure configurations,
loss of visibility is increased due to the loading on deck of container boxes. This
blind area forward is and likely will remain a fact of life for the mariner aboard a
vessel with an after bridge. However, aft superstructures nevertheless aid in
vessel maneuvering, because the response of the whole ship relative to maneu-
vering commands and the channel or waterway unfolds in front of the person
piloting the vessel. On a forward superstructure ship, there is a loss of visibility
aft. This is aggravated on ships such as car carriers, where high superstructures
extend almost the full length of the ship. This is a disadvantage in pilotage
waters, because the view aft is obstructed, making it more difficult to visually
ascertain ship motion relative to a confined waterway and other vessels that may
be approach from abaft of the beam.
Because visual navigation has been the primary means of maneuvering a
ship, albeit supported by various modern navigational aids, the bridge almost
always is surrounded- to the extent possible by windows. In fact, at times
essential information can be acquired or supplemented reliably only with the
eyes; such information may include, for example, the presence of small craft and
their maneuvers, fishing nets, tide rips, and vessel behavior relative to operating
conditions (such as maneuvering behavior in shallow water). Therefore, the need
for good visibility will not be diminished appreciably by the introduction of new
positioning technology, even in those cases where the technology by itself effec-
tively supports ship navigation.
In modern ships, bridge wings usually are constructed to flare from the sides
of the bridge. This allows the person piloting the vessel to change positions to
obtain the best view for each maneuvering evolution or to check specific aspects
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436
APPENDIX G
of an evolution, such as movement toward a pier during docking. Bridge layout
and procedures also have been designed to facilitate visual navigation. For ex-
ample, the steering stand usually is located on the centerline of the ship and
somewhat back from the front of the bndge.
A gyroscopic (gyro) compass repeater normally is mounted above the steer-
ing stand on modern ships, although on many older ships the steering stand is
configured as a binnacle, on which the gyrocompass repeater is mounted (with
the gyrocompass usually located off the bridge). A magnetic compass normally
is mounted in the binnacle (or in a holder mounted on or in front of the steering
stand). The magnetic compass was retained to provide a means to detect mal-
function aIld error as well as to back up the gyrocompasses before they were
proven reliable (magnetic compasses still serve a general backup function).
On most ships, propulsion is controlled or ordered from a stand or console
located near the steering stand. On modern ships, some form of console usually
extends outboard on one or both sides of the steering stand; several groups of
controls, switches, and enunciators are located on the console for managing com-
munications, lights, engine and steering alarms, horns and whistles, and other
systems the person conning the vessel might need. Radars usually are located
outboard of the console and slightly forward. Most ships have two radars, one or
both of which are configured as, or connected to, an Automatic Radar Plotting
Aid (ARPA).
An instrument board usually is located forward of the steering stand, above
the windows. This long, narrow panel contains a clock and indicators for rudder
angle, engine revolutions per minute, gyroscope heading, ship speed, and depth
under keel or water depth. The panel also may include displays that are useful
during maneuvering, such as a rate-of-turn indicator or a docking Doppler.
Aft of the steering station is the chart room. This may be an actual room or
simply an area that can be closed off at night with curtains or panels to prevent
its light from flooding the steering area. The main feature of the chart room is
usually a rectangular table, where the navigator can spread charts for voyage
planning, plotting the ship's trackline, and so forth. There is normally a chart
table on the bridge, where actual position plotting is accomplished. Navigation
instruments are usually located nearby, although some may be placed in the
chart room. These instruments generally include traditional equipment for celes-
tial navigation, such as the sextant and chronometer, and some or all of the
electronic navigation displays and controls. Electronic navigation refers to all
techniques and systems that rely on electronic devices, including radio, radar,
Loran C, and satellite navigation systems such as Transit and the Global Posi-
tioning System.i
Electronic navigation also refers to inertial, bathymetric, and Doppler navigation, which have not
attained broad use in merchant shipping. Inertial systems provide accurate dead reckoning (if they
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A PRIMER ON NAVIGATION TECHNOLOGIES
437
The chart room also has numerous drawers and shelves for storage of plot-
ting instruments, charts, almanacs, manuals, and other books and devices the
navigator needs to plan and plot the ship's track and courses, and to determine its
actual track and speed made good.
The walls, stands, and shelves around the periphery of the bridge usually
contain other panels and instruments. These often include receivers for facsimile
copies of weather forecasts and for automated notices to mariners, as well as
other specialized systems. Repeaters showing information from other instruments
also may be mounted in these areas, so the mariner can roam the bridge. Com-
mur~ications transceivers or repeaters often are placed in areas where the watch
officer stands during maneuvering tasks.
The equipment used most often by pilots includes the gyrocompass, radar,
Loran C, VHF radio, and various indicators (Ramaswamy and Grabowski, 19921.
NAVIGATION TECHNOLOGIES: KEY FEATURES AND USES
The anemometer indicates the speed and direction of the wind-essential data
for estimating the compass heading required to achieve a desired course, part~cu
larly when maneuvering in strong winds.
Automated docking systems/docking assist systems comprise advanced sensor
technologies (using velocity derived from lasers, microwave ranges, or Differen-
tial Global Positioning System EDGES]) and computer technologies such as fuzzy
topic or neural networks. Autonomous systems have yet to be deployed, but a
number of experimental docking-assist systems are undergoing evaluation aboard
operating vessels. Such systems usually include a ship-posit~oning system, a
berthing and unberthing control system, and a communications system linked to
the tugboats. Some docking systems may include a geographical representation
of the ship's position, integration with the gyrocompass and steering system, and
sophisticated control algorithms.
Automatic Dependent Surveillance (ADS) is a concept involving integration of
data functions and the sharing of data through automatic NTHF data broadcasts
among Vessel Traffic Service (VTS) systems and ships in the area. The data to
be shared is expected to include ship identification, course, speed, position, and
possibly intent (based on the next waypoint in a voyage plan). The DGPS is the
are updated regularly using another navigation device) but would be costly for merchant use. Bathy-
metric navigation is an old technique that uses the topography of the ocean floor to determine
position; technological advances may transform this technique into an important complement to
other systems. Doppler (acoustic) navigation does not appear to have made inroads in merchant
shipping.
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438
APPENDIX G
sensor of choice for most of the information. The data could be displayed on a
digital radar screen, an electronic chart system, or on a stand-alone monitor. Use
of ADS will help ensure that all parties are aware of the presence and intentions
of ships in the area and that all are working with the same data; effectiveness of
ADS depends on the number of vessels equipped with the system. The Coast
Guard is requiring the use of ADS on all tank vessels of 20,000 deadweight tons
or more in Prince William Sound, Alaska (33 CFR Part 161, revised July 17,
1992).
Automatic Dependent Surveillance Shipborne Equipment (ADSSE, is carried by
vessels participating in an ADS scheme, to provide VTS systems and, if desired,
other nearby vessels, with ship surveillance information. This equipment fea-
tures an automatic broadcast of ship identification, course, speed, and position,
derived from an onboard navigation system. The broadcast also could contain
intent data based on the next waypoint. The sensor of choice is DGPS equipment
with the data is transmitted via VHF radio channelks). The Coast Guard is requir-
ing ADSSE on tank vessels of 20,000 deadweight tons or more using the VTS
system in Prince William Sound, Alaska (33 CFR Part 161, revised July 17,
1992~. (See "Vessel Traffic Services.")
Automatic Radar Plotting Aid (ARPAJ is a computer that quickly and automati-
cally plots radar targets and is used to assess passing and overtaking situations.
ARPA typically obtains information about the course from the gyrocompass,
speed from the Doppler speed log, and target positions from a radar, which
sometimes is built into the ARPA. ARPA can help prevent collisions in open
bays and sounds; its collision-avoidance feature is of lesser utility in narrow
channels (Zabrocky, 19921. This operating characteristic stems from the nature
of ARPA, which averages large amounts of inexact data to calculate a target's
probable past course and then projects that information into the future; the de-
vice simply does not have the resolution to solve problems involving close en-
counters, nor has the technology been able to generate solutions quickly enough
for transits requiring frequent maneuvering, such as in narrow, winding channels
in waterways and rivers.
An autopilot is a computer that steers a programmed course by sensing devia-
tions from the true course (determined by gyrocompass) and compensating with
changes in rudder angle. An autopilot may also be used to keep the ship on a
passage plan trackline based on cross-track error information from electronic
navigation instruments capable of storing voyage plans. Some autopilots can
steer the ship toward a defined waypoint with or without correction for drift but
without regard to cross-track error. Some newer systems execute turns automat-
ically with a constant rate or radius to finish at a preset heading or to intersect
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A PRIMER ON NAVIGATION TECHNOLOGIES
439
with the next leg of the voyage plan. Autopilots, in varying levels of sophistica-
tion, are in near-universal use on deep-draft vessels.
Beacons are used as lighted and unlighted reference points for ships, to prevent
groundings and help with alignment in channels.
Buoys are used as lighted and unlighted reference points for ships, to prevent
groundings and help with alignment in channels. Radar-reflecting buoys give an
electronically enhanced radar signal.
Constant tension winches are used to maintain pressure on wire ropes holding a
ship against the pier as the ship changes draft (due to loading or unloading) and
as winds and currents change. With manually adjusted winches, the crew must
be alert to adjustments needed to prevent ropes from snapping under excess
tension and to prevent the vessel from surging against the dock under slack lines.
A course recorder makes a pen-and-ink record on a paper chart roll to record
courses steered and course-keeping quality. This equipment is in wide use on
deep-draft vessels but a significant number of ships lack this equipment.
Decca is a long-range radio navigation system that is less accurate than the
Global Positioning System (GPS). Decca is expected to be phased out around the
turn of the century.
The depth sounder is used to monitor the depth of water under the keel. It
features an analog or digital display of water depth. Some units have a depth
alarm feature. This equipment is in almost universal use on deep-draft vessels.
The Differential Global Positioning System (DGPS) provides the capability ac-
curate position fixes in harbors and harbor approaches by using data broadcasts
(by the Coast Guard in the United States) to correct GPS signals. The DGPS is
scheduled to be in place in 1996, when the differential corrections will be trans-
mitted through marine radio beacons located along the U.S. shoreline. The
present attainable 2 dRMS (distance root mean square) accuracy of DGPS is
roughly 5 to 10 meters (USCG, 19921; accuracy may improve with the next
generation of GPS receivers, as receiver errors (noise and multipath) are mini-
mized (Cannon and Lachapelle, 1992~. The DGPS is expected to increase the
accuracy of vessel navigation, VTS surveillance, and onboard plotting of other
vessels (Alsip et al., 1992~.
Digital Selective Calling (DSC) is the international standard for data communi-
cations in maritime mobile communications service. In the VHF band, DSC is a
1,200-baud, character-oriented data link.
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440
APPENDIX G
The Doppler speed log uses reflected sonic emissions to calculate vessel speed
through the water and, in some cases in relatively shallow water, speed over
ground. Outputs are used by the ARPA to calculate collision-avoidance data and
by electronic navigation instruments to calculate set and drift, or for dead reck-
oning by the ARPA when the water signal is lost. The Doppler speed log fea-
tures a digital display of speed fore and aft and athwartships. It is in common
use, but a significant number of ships lack this equipment.
Dual-Axis Docking Doppler Systems provide two Doppler speed logs, one for-
ward and one aft, configured to measure speed over ground both longitudinally
and horizontally. By observing speeds on a combined display, the mariner can
control the ship fairly well while docking. These systems are used only on very
large ships due to their high cost and marginal utility for smaller ships.
Electrohydraul~c Steering Control sends an electric signal from the steering
wheel on the bridge to a hydraulic steering engine (which is connected to the
rudder) to cause the rudder to move in proportion to the wheel movement.
An electronic chart is a digitized version of a nautical chart, with graphic repre-
sentations of water depth, shorelines, topographical features, aids to navigation,
and hazards (Eaton, 1990; Eaton et al., 1990; Gold, 1990b; Landreth, 1991;
Rogoff, 1992~.
The origins of the electronic chart date back to the use of mechanical plot-
ters by the military during World War II. Video plotters later were developed
that used data from Loran C or other continuously operating systems; the addi-
tion of coastlines and navigational aids to the video plotter screen led to the
evolution of the electronic chart (see Rogoff, 1990~. Although the technology
has been available for over a decade, interest in electronic charts has soared
recently with the availability of reasonably priced computers for rapid manipula-
tion of large amounts of chart data.
At present, electronic charts have no legal status and are used only to sup-
plement paper charts. The SOLAS convention requires that all ships carry charts;
although not stated explicitly, it is understood that this refers to paper charts
(Mensah, 19901.
An electronic chart offers little improvement over the paper chart unless it is
combined with other information or data presentation features. At a minimum,
the ship's position (from Loran C or the GPS) and planned track are needed; also
useful are an overlay or underlay of a radar image, electronic bearing lines,
velocity vectors, ARPA data, and warnings and alarm information (see Electron-
ic Chart System and Electronic Chart Display and Information System LEC-
DIS]~. Use of electronic charts on large commercial vessels has been limited,
because international standards have yet to be approved for ECDIS and because
of the limited availability of suitable electronic charts.
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A PRIMER ON NAVIGATION TECHNOLOGIES
441
Electronic chart system (ECS) is a generic term referring to systems that display
an electronic chart on a computer monitor. Such systems are not the legal equiv-
alent of a paper chart, and the hydrographic data base used need not be "official"
(i.e., provided by a national hydrographic office). Electronic positioning is re-
quired, and a radar overlay is optional. Such systems are in use on some com-
mercial vessels as a navigation aid, with paper charts fulfilling the legal carriage
requirement. Standards for ECS are under revision by the Radio Technical Com-
mission for Maritime Services SC-109 Category 3 Working Group.
An Electronic Chart Display and Information System (ECDIS) receives position
data from radio navigation instruments and integrates it with a voyage plan and
an "official" hydrographic data base to provide a real-time display of the ship's
position with respect to the chart and voyage plan. Electronic positioning is
required, and a radar overlay is optional. First-generation models are in limited
use on some advanced ships (Akerstrom-Hoffman et al., 1993; Alexander and
Black, 1993; Ganjon, 1991; Gonin, 1993; Lanziner et al., 1990; Rogoff, 1992;
Royal Institute of Navigation, 1993; C. Weeks, 1992~.
ECDIS is a specific type of electronic chart system that eventually will use a
data base provided by a national hydrographic officer and meet international
standards. An international evaluation of draft performance standards is under-
way, and, once generally accepted standards are approved,3 ECDIS may be con-
sidered equivalent to paper charts (Mensah, 1990~. (The full planned capabilities
of ECDIS are detailed in the Draft Assembly Resolution, Performance Standard
for Electronic Chart Display and Information System, IMO Maritime Safety
Committee, MSC/Circ. 637, May 27, 1994.)
ECDIS is expected to become a basic navigation technology in the future, as
radar and voice communications are today. Indeed, some experts assert that it is
only matter of time before ECDIS becomes mandatory (CHA, 1990~. Draft leg-
islation has been proposed that would make ECDIS mandatory for operations in
United States waters. This draft legislation has come under criticism, because
requiring specific technology rather than equipment that met performance objec-
tives would be required could potentially constrain the development of electron-
ic positioning systems (Chapter 61.
The engine console is used to control the main propulsion system and thrusters.
It features Engine Order Telegraph or direct throttle control of main engines,
lever control of bow and stern thrusters, and readouts of engine performance.
2The National Oceanic and Atmospheric Administration is developing a standardized, fully attrib-
uted electronic chart for use in ECDIS, but progress is slow, so leading equipment vendors and
suppliers are developing their own electronic charts, which vary in content and completeness.
3The earliest this could happen is the IMO General Assembly in the fall of 1995 (Donald Florwick,
NOAA, personal communication, October 30, 1992).
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APPENDIX G
Engine order telegraph is in almost universal use on deep-draft vessels, and
direct throttle control is in wide use. Thrusters are installed on selected vessels.
Expert systems see piloting expert systems.
Fog signals are used as reference points for ships in order to prevent groundings
and collisions. Signals include the diaphone, horn, bell, whistle, and gong.
The Global Maritime Distress and Safety System (GMDSS) is a telecommunica-
tions concept for ships that encompasses equipment such as radio communica-
tions devices, Emergency Position Indicating Radio Beacons (EPIRB), and sat-
ellite terminals. The 1988 amendments to SOLAS specify minimum carriage
equipment based on routes travelled and other variables. The GMDSS is in uni-
versal use, effectively making Morse code obsolete (Brodje, 1992; Fairplay,
1992b; IMO, 1986).
The Global Positioning System (GPS) is a Department of Defense radio naviga-
tion system using transmissions from satellites. It will provide very accurate and
continuous worldwide position fixes in three dimensions through its initial con-
stellation of 24 satellites. The GPS is scheduled for initial operational capability
by the summer of 1993 and full capability by mid-1994.
For civilian users, GPS provides horizontal accuracy to 100 meters, 2 dRMS
(DOT and DOD, 1993), or approximately 95 percent accuracy. This 100-meter
accuracy is a result of deliberate degradation of the system by the Department of
Defense; normally, accuracy would be in the 20- to 30-meter range (Donald
Florwick, NOAA, personal communication, October 30, 1992~. To overcome
this performance limitation and to minimize other systematic signal errors, GPS
can be augmented by differential corrections to its range measurements (USCG,
1992), based on the precise location of a reference antenna. (See Differential
Global Positioning System.)
A key feature of both GPS and DGPS is that the equipment is accurate and
easy to use, meaning that some traditional navigation skills are not required for
its operation. The receivers display latitude and longitude directly, so the user is
required merely to plot them correctly or have them displayed on an electronic
chart. Moreover, the receivers are small, which facilitates the design of compact
navigation stations. The ease of use reduces human collection and processing
requirements, thereby providing more time for interpretation and use of naviga-
tion information. It also gives the watchstander time to attend to other bridge-
team tasks.
GLONASS is a Russian satellite navigation system similar to the GPS. It is ex-
pected to provide accuracy of about 30 meters without differential corrections
(Eastwood, 1990; Kinal and Singh, 1990; Nilsson, 1992~.
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A PRIMER ON NAVIGATION TECHNOLOGIES
443
The gyroscopic (gyro) compass uses the spatial stability of the gyroscope to
provide a display of true heading. The gyrocompass features azimuth repeaters
for visual bearings and course monitoring, and digital repeaters for course mon-
itoring. Outputs from the gyrocompass can provide signals to the autopilot, rate-
of-turn indicator, ARPA, electronic navigation instruments, course recorder, sat-
ellite communications antenna, and ECDIS; gyrocompass outputs provide
heading data for calculating steering corrections, set and drift, rate of turn, dead-
reckoned course, and alignment to changes in heading. Gyrocompasses and azi-
muth repeaters are in almost universal use on deep-draft vessels, and digital
repeaters are in wide use.
Hull stress monitoring systems make use of structure-mounted sensors and comput-
er models of the ship hull to provide expert advice on safe speed and heading.
These systems help minimize potentially dangerous conditions in severe weather.
An Integrated Bridge System (IBS) provides all information essential to naviga-
tion and piloting at a central command-and-control station, thereby reducing risk
and allowing for reduced crew size. An IBS combines an electronic chart sys-
tem, a positioning system, and other traditional or newly developed displays,
sensors, controls, processors, and panels in one compact console. This console is
placed in the area of the bridge that provides the best view for visual lookout, so
the ship can be maneuvered by one person, and there is no need to build the
complicated and error-prone communication links of the traditional command-
and-control chain (see description of the traditional bridge at the beginning of
this appendix). The IBS configuration is similar to that of an airplane cockpit,
although visibility covers a substantially larger field of view. Some new ships,
particularly in Northern Europe, have IBS (Alexander and Spalding, 1993; Gill,
1989; Hederstrom and Gylden, 1992; Kristiansen et al., 1989; Maconachie, 1990;
Marine Log, 1993; Roeber, 19921.
The Integrated Ship Control System (ISCSJ is an extension of the integrated
bridge concept wherein engineering and cargo/ballast functions are integrated
with the navigation systems on the bridged It is becoming easier to establish
links among the various systems, as almost all new ships are built with inte
4There is merit in such integration. Coordination between the bridge and the engineering plant is
needed to ensure proper control of the engines, including anticipation of pending changes in speed or
direction. The safe maneuvering of the ship also demands proper management of electric power,
control air, and starting air resources. Likewise, to provide and maintain proper trim and stability, the
crew needs to control ballast and cargo levels. Ideally, all information and operating functions
needed while the ship is underway could be placed in a single console at the normal maneuvering
position.
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APPENDIX G
grated, digital engine-control systems and many utilize similar systems for cargo
and ballast control. Several ships with ISCS technology have been built by sev-
eral foreign operators (Herbergeret al., 1991; Kristiansen et al., 1989; O' Neil,
1990~. In these ships, the engine, ballast, and cargo control consoles have been
relocated to the bridge.
Some existing ships with ISCS are operated by specially trained dual-pur-
pose officers, while other ships retain the traditional split between the deck and
engine crew (i.e., the deck officer must call for an engineer when an engineer is
needed). If fully integrated systems and one-person bridge operation become
feasible, then operating requirements and ship design would have to be evaluat-
ed very carefully, and the single watch officer would need a new range of skills
and training. Of particular concern would be the design of the ship and its sys-
tems to prevent an overload of information and work on the watch officer. New
technologies are being developed to address these concerns (see "Piloting Expert
Systems".
Lights are used as shore reference points for ships, both to prevent groundings
and to help with alignment in channels. Lights include fixed light structures,
major floating lights, and ranges (e.g. lights in line).
Loran C is a radio navigation system that provides latitude and longitude coordi-
nates for harbors and their approaches, with accuracy of 0.25 nmi (2 dRMS) or
better (DOT and DOD, 19931. (The Loran's repeatability is significantly better
than its accuracy.) The Loran is used to fix navigational position. It is in wide
use on deep-draft vessels.
The magnetic compass is used primarily to set and monitor the gyrocompass, but
it also may be used as the primary heading instrument. The magnetic compass
typically is mounted on the flying bridge with periscope viewing. It is in almost
universal use on deep-draft vessels.
The nautical chart is a graphic representation on paper of navigable waters,
showing water depth (by soundings or depth contours), shorelines, topographic
landmarks, aids to navigation, hazards, and other information of interest to mar-
iners. Many vessels are required by law to carry nautical charts, which are in
universal use.
Omega is a long-range radio navigation system with accuracy of 2 to 4 nmi.
Differential Omega has an accuracy of 0.3 nmi within 50 nautical miles of a
reference antenna, and 1 nmi at 500 nautical miles (DOT and DOD, 19931. It is
not widely used and is expected to be phased out around the turn of the century.
The Physical Oceanographic Real-Time System (PORTS' is a technology devel
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A PRIMER ON NAVIGATION TECHNOLOGIES
445
oped by the National Ocean Service that is designed to overcome limitations of
traditional prediction tables (published annually) that provide only the astronom-
ical tides and currents. The system employs sensors placed at multiple locations
within a port to measure real-time water level, current velocity, wind velocity,
and water temperature. The initial test installation in Tampa provides data on
hourly radio broadcasts and allows real-time voice data to be received by tele-
phone or text data to be received by telephone modem (Appell et al., 1991;
Bethem and Frey, 1991; Frey, 1991; NOS, 19903.
Piloting expert systems are computer programs designed to combine the lmowl-
edge and reasoning process of expert operators and to recognize the need for
advice and provide it. Real-time input from numerous sensors is required for
these systems to recognize and interpret the need for advice. Shipboard piloting
expert systems are under development in many countries as part of "intelligent"
ship projects (Grabowski, 1987, 1989, 1990; Hartman, 1990; MARAD, 1988~.
The very comprehensive U.S. Shipboard Piloting Expert System (SPES) is an
intelligent node in an IBS.s In addition, a number of stand-alone systems are
being built by a variety of manufacturers in the United Kingdom, Norway, the
European Community (the Expirt KBS Ship Project), Gerrrlany, Japan, and South
Korea (Iijima and Hayashi, 19911.
The Portable Communication, Navigation, and Surveillance (PCNS) system is
conceived as a small unit that could be carried aboard vessels by a pilot. The
primary components are a DGPS receiver with an electronic chart display and a
VHF radio. The ECUS would provide many of the benefits of ADS before wide-
spread implementation of ADS systems. A number of pilot organization and
instrument manufacturers have shown interest in developing and testing this
concept.
Numerous publications are essential to navigation. The Local Notice to Mari-
ners, published by each Coast Guard district, contains chart corrections and
other information of local and wide interest. (Summaries are contained in Week-
ly Notice to Mariners, published by the Defense Mapping Agency Hydrograph-
ic/Topographic Center.) Tide Tables and Tidal Current Tables is produced annu-
ally by the National Oceanic and Atmospheric Administration (NOAA); the
information also may be obtained by modem.
A series of nine U.S. Coast Pilots, published regularly by NOAA, provides
irr£ormation on domestic navigation regulations, outstanding landmarks, channel
SThe Shipboard Piloting Expert System program, under development by Rensselaer Polytechnic
Institute, is sponsored by the Maritime Administration and the Coast Guard, with cost sharing by
Sea-River Marine (formerly Exxon Shipping Company) and Sperry Marine.
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APPENDIX G
peculiarities, dangers, weather, ice, port facilities, and other features of interest.
Similar information for waters outside the United States can be found in Sailing
Directions, revised as needed by the Defense Mapping Agency Hydrographic/
Topographic Center. The rules of the road for navigating inland U.S. waters and
the high seas can be found in Navigation Rules, published by the Coast Guard.
The Nautical Almanac, published annually by the Naval Observatory, contains
astronomical information needed for celestial navigation. The Light List, pub-
lished annually by the Coast Guard, contains information on lights and sound
signals, unlighted buoys, radiobeacons, radio direction finder (RDF) calibration
stations, racons, and Loran stations in U.S. coastal waters, the Great Lakes, and
the Mississippi River. Similar information for other coasts can be found in the
List of Lights, published annually by Defense Mapping Agency Hydrographic/
Topographic Center.
Racons are aids to navigation that give an electronically enhanced radar signal.
Also known as radar transponder beacons, racons may respond with Morse code
in the 3 cm or 10 cm bands.
Radar, second only to the gyrocompass, is probably the most important tradi-
tional aid to navigation available to the marine pilot. Radar can measure range
and bearing accurately and quickly and can feed data to other equipment, such as
ECDIS. Existing radar technology is not wholly adequate, however. Pilots re-
sponding to the committee's correspondence said their most pressing technolog-
ical need was for a highly improved radar system, particularly with improved
target acquisition during squalls (Ramaswamy and Grabowski, 19923.
Radar marks are used as shore reference points for ships, to prevent groundings
and to help with alignment in channels. Such marks include remark (radar bea-
con transmitting continuously), racon, radar reflectors, and the new circular po-
larized radar reflectors (used with a special radar for accurate positioning in
piloting waters).
Radio beacons are AM radio stations used with radio direction finders on ships.
The position fixes provided by this system no longer meet modern requirements,
but, as the system has been chosen to carry DGPS broadcasts, it is likely to
continue in use.
The Radio Direction Finder (RDF) is a short-range navigational aid using radio
beacon bearings that is used to fix navigational positions. The RDF is installed
widely, but its utility is diminishing with the advent of more sophisticated aids.
The rate-of-turn indicator uses outputs from the gyrocompass or an internal
gyroscope to display the rate (in degrees per minute) at which the ship is chang
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A PRIMER ON NAVIGATION TECHNOLOGIES
447
ing heading. The display may be analog or digital; most of these indicators also
provide an audible report. This indicator is in wide use on deep-draft vessels;
however, a significant number of ships lack this equipment.
The recording barometer measures and records, on a chart, the atmospheric
pressure. By observing the pressure and rate and direction of change, the watch
officer can predict changes in weather and the likely severity of the weather.
Repeaters are displays showing information from remote instruments.
The revolutions-per-minute (RPMJ indicator is used to monitor the propulsion
system. It features an analog or digital display of engine, shaft, or propeller
RPM. It is in almost universal use on deep-draft vessels.
Routes see tracks.
The rudder is a flat structure of wood or metal attached vertically to the ship's
stern. The rudder is used for directional control of the vessel; when it is turned,
the ship's bow turns in the same direction.
The rudder angle indicator is used to monitor the rudder. It features an analog
display in degrees. It is in almost universal use on deep-draft vessels.
The steering stand is a console where the steering wheel, rudder angle indicator,
autopilot, and backup steering systems are mounted. This equipment is used for
course keeping and navigation and is in almost universal use on deep-draft ves-
sels.
Tide Tables see publications.
The tiller is a lever used to turn the rudder in steering.
Tracks and routes are used for safe routing of ships, to prevent collisions and
groundings. Tracks and routes include traffic separation schemes, precautionary
areas, inshore traffic zones, deep-water routes, and recommended routes. Tracks
and routes are especially common in port approach and coastal confluence areas.
Transit (Navy Navigation Satellite System, or NAVSAT) is the original satellite
navigation system. It consists of five satellites orbiting the Earth at an altitude of
almost 700 miles. Transit is used for position fixing on many seagoing vessels.
Its accuracy varies from 25 to more than 500 meters, depending on the equip-
ment and the user's knowledge of the ship's velocity. System coverage is global,
but not continuous (DOT and DOD, 19933. The system probably will be phased
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APPENDIX G
out slowly In preference to the GPS. (The 1992 Federal Radionavi~gation Plan
EDOT and DOD, 1993] calls for termination of Transit in December 1996.)
Vessel Traffic Service (VTS) systems are a form of marine traffic regulation.
VTS overlays a port and waterways complex with an organizational structure
that enhances communication and interdependent decision making between ves-
sels, improves order and predictability, and provides a capability for real-time
operational oversight and traffic management by port safety and management
authorities. This structure may be enhanced by establishment of traffic lanes
where feasible. A VTS provides information to vessels in transit about vessel
traffic and other hazards in waterways, harbors, and harbor approaches and,
depending upon the operational concept employed, may also provide advice or
conduct traffic or anchorage management. (For an extensive discussion of VTS,
see Chapter 5.) (CCG, 1992; Cutland et al., 1988; Glansdorp, 1987; Herberger et
al., 1991; Hofstee, 1990a; Ives et al., 1992; Maio et al., 1991; Mizuki et al.,
1989; Polderman et al., 1990; Young, 1994.)
Weatherfacsimile receivers can be programmed to receive forecasts and weather
maps of the area in which a vessel is sailing. They produce printed copies of this
information, allowing the mariner to study the data and plan route changes or
other preparations for expected weather conditions.
Weather routing services provide weather monitoring and prediction assistance
as well as recommendations for changes in voyage plans to avoid severe weather
or to take advantage of (or avoid) ocean currents. These services have been
shown to save time and fuel in long ocean passages and to reduce costs related to
damage and repair.
Representative terms from entire chapter:
navigation technologies
