The Bridge is a Navigational Aids and Ship’s Bridge Simulator;
replicating the layout and navigational instrumentation present
on a modern ship’s bridge. As you will see, this simulator also
replicates, using real imagery, the scenery associated with
major ports throughout the world.
Passages in and out of Dublin, Liverpool, Dover, Calais and
ports around Glasgow can be undertaken as if for real on several
different types of vessel.
The purpose of this simulator is to train both professional and
part-time mariners in the use of new forms of navigation
equipment and to learn how to handle a vessel in any situation.
In the last decade marine navigational aids have changed
considerably both in capability and in sophistication.
Heretofore, the practice of marine navigation was more related
to calculating position using compasses, sextants, paper charts
and a variety of manual and sometimes time consuming methods.
Nowadays, however, navigation is more related to the practice of
position monitoring thanks to the acceptance of computer and
satellite technology and their quick introduction onto modern
ships and smaller vessels. The speed of these systems permit a
large degree of automation in the guidance of vessels, however,
modern professional and part-time mariners are still taught and
expected to be proficient in traditional techniques in order to
check their systems and be prepared for when the power goes
On Our Bridge are all the instruments you would encounter in a
modern ship’s bridge, trawler’s wheelhouse or yacht’s
charthouse. The concerns of the navigator in all cases are to
ensure that his/her vessel is interacting safely with the
immediate environment and other vessels, bearing in mind weather
and tidal conditions and all other hazards associated with
following the planned route.
The invention of radio as you can see in the display about
Marconi in Crookhaven had great benefits for the seafarer.
Emergencies and accidents at sea could be reported immediately.
As radio became more popular the airwaves became so busy that a
frequency, which could be used by fewer people, was needed for
use in emergencies. So Very High Frequency radio marine channel
was developed as a licensed service with an annual fee. Around
our coastline Channel 16 is still used as an international
calling and distress channel in addition to more modern
arrangements using Channel 70. Our radio is on Dual watch,
meaning that it is listening to both Channel 16 and Channel 23
where the Irish Coast Guard broadcast Weather and Navigation
warnings on a regular basis. This radio is not simulated and any
broadcast heard, including distress broadcasts, is for real.
The barograph is an aneroid barometer with a facility for
continuously recording the changing air pressure. Unlike mercury
barometers in which mercury changed level depending on the
weight of the air on it (higher for high pressure and lower for
low), aneroid barometers have a drum containing a vacuum sealed
at a particular air pressure. As the air pressure changes, the
drum expands and contracts. In the barograph, a pen attached to
the lid of the drum draws ups and downs on a rotating sheet of
Changes in air pressure are related the movement of air in our
atmosphere. High-pressure areas (greater than 1013 millibars or
hectopaschals) are those areas where there is an inflow of air
in the adjacent atmosphere. Similarly areas of pressure less
than 1013 millibars or hectopaschals are low-pressure areas
where there is an outflow of air. High-pressure zones
(anticyclones) are associated with fair weather while fronts and
low-pressure zones (depressions) are associated with wet, stormy
weather and high winds.
The barograph is still used aboard many vessels nowadays, not so
much to record accurate pressure, but more to show the tendency
of atmospheric pressure. For example a sudden decrease in
pressure and a resulting dip on the paper graph would be a very
strong indication to the mariner that high winds are on the way.
Clock or Ship’s Chronometer
For seafarers a clock is not just to tell the time, it is an
important part of navigation. Many will be familiar with
Harrison’s long struggle to invent a timepiece that would be
accurate aboard a ship given that ships are subject to excessive
movement. For those with an interest in these matters, the
award-winning book “Longitude” by Dava Sobell is recommended as
a very informative and easily read explanation of the
development of time for measuring longitude at sea. It remains
the practice in marine and air navigation to define position by
reference to Latitude and Longitude, Latitude traditionally
being listed first as it was always the easier to calculate. The
calculation of Longitude relied on measuring one’s movement east
or west of the start point very accurately. This could only be
done well if time could be measured easily; i.e. showing a
relationship between ship’s movement and the east to west
movement of the sun or indeed of any other heavenly body.
Harrison’s Chronometer greatly assisted the calculation of
Longitude in conjunction with the Octant, the astrolabe and most
recently the Sextant.
The sextant is an instrument designed to measure angles very
accurately – typically to a 10th. of a minute. It does this by
using a system of mirrors. Light from a distant object, such as
a star or lighthouse, is reflected by the index mirror down to
the horizon glass and from there back down to the telescope.
Only half of the horizon glass is silvered so that the observer
can look through the telescope and the horizon glass at the same
time. The effect is to look two different directions at once.
Moving the index arm can change the angle between these two
directions and it can be read off a scale. The main index scale
is written in degrees and minutes are shown on the micrometer
drum for precise adjustment.
In calculating a vessel’s position, a sextant is used to measure
the angle between the observer’s horizon and a heavenly body,
such as the sun, moon, planet or the 57 navigational stars. Once
this angle is known, a spherical triangle created between the
observer, the Pole and the Body can be resolved by traditional
spherical trigonometry and the result compared to an estimated
position, which can be adjusted accordingly. This is only
possible knowing accurate time, having an estimated position and
referring to the nautical almanac which documents the position
and movements of all the heavenly bodies used for navigation.
Mariners still carry sextants and yacht masters and
professionals alike are still required to be able to use them in
the event that modern equipment fails to function.
This works on the same principal as the barograph but is used
more to measure actual pressure as an indicator of expected
Within the earth’s atmosphere, depressions and anticyclones are
continually developing and dying. Some last a day or two; others
(in particular, large anticyclones) can last for weeks. The
depressions that affect Western Europe develop over the Atlantic
Ocean where cold polar air meets warm tropical air and they move
east steered by the river of air in the stratosphere. The
boundary between the two is called a pressure front. As the
buoyant lighter warm air (high pressure) rises over the denser
heavier cold air (low pressure) and the cold air gets under the
warm air. The warm front comes ahead of the cold air and as the
front builds, the two get energy from each other, they swirl
around each other and the winds strengthen. As the air collects
and gets heavier the pressure drops; the wind blows harder, the
clouds thicken and the rain starts.
Air masses are like mountains and valleys but instead of using
contour lines to map them, lines of equal pressure above sea
level are used. These lines of pressure are called isobars. They
join areas of equal barometric pressure. Pressure is measured in
millibars or hectopaschals. A steep change in pressure between
adjacent isobars means a strong wind and small change means a
Long before meteorologists understood about the workings of
depressions, sailors used barometers to warn them about
approaching storms. A rapid drop in air pressure was a sure sign
of bad weather to come. The barometer is still the most
predictable way to predict storms for the amateur meteorologist.
The development of GPS (Global Positioning System) by the US
Government started in 1973 and it became fully operational in
1995. Having been first used for military purposes in the first
Gulf War in 1991, GPS has been rapidly adopted for many civilian
uses, most notably for marine navigation. Nowadays, standard GPS
can offer the user position accuracy of 15 metres or better and
this is possible anywhere in the world, irrespective of weather
or time of day.
The GPS constellation consists of 24 satellites orbiting at an
altitude of 11,000 miles. Each satellite continuously transmits
a coded signal on two microwave frequencies – roughly 10 times
higher than marine VHF and - including a message that says ‘I am
here’ and ‘the time is now’. The codes on the two frequencies
are different and only one, called the CA code (for Coarse
Acquisition) is available to civilian receivers.
The signal takes time to travel from the satellite to the
receiver, so it is received slightly later than it is sent.
Microwaves, like any other radio waves, travel at an almost
constant speed of 300,000 Kilometers per second, so the
difference between the time of transmission and the time of
reception corresponds to the distance between the satellite and
the receiver. If the signal arrives one tenth of a second after
it was sent, the receiver is 30,000 Km from the satellite – that
is, it is on the surface of a sphere with a radius of 30,000 Km,
centered on the satellite. If the same thing is done
simultaneously with the three satellites, then position of the
receiver can be pinpointed.
Marine Navigation in coastal regions very often requires
position accuracies better than those possible from ordinary
GPS. To provide these accuracies, The Commissioners of Irish
Lights provide a Differential GPS service, which broadcasts
corrections to the GPS Satellite signals, and position
accuracies of better than 1 meter are now possible using these
corrections. The corrections are broadcast using a medium wave
transmitter and the tall mast behind this Centre is one of three
in Ireland and 12 between the UK and Ireland. There are many
similar stations in Coastal areas of the US, Australia, New
Zealand and much of Northern Europe. For this reason Mizen Head
is an important location for the safety of Navigation in
The instrument shown on the wall is giving an accurate
indication of the location of GPS satellites overhead at any
particular time. This GPS is not simulated and is giving a real
Latitude and Longitude position for our Centre as calculated
from the GPS satellites.
The anemometer is used to measure wind speed and direction. The
most common form used is the spinning cup anemometer invented in
1846. As the cups rotate, the spindle triggers an electrical
contact so that the number of rotations in a given time is
recorded and wind speed thereby calculated. The instrument shown
is not a simulator, however real wind speed and direction may
not be accurately shown as wind eddies falling from the hill
behind do adversely affect our spinning cup sensor on the roof.
At sea wind speed and direction are key information for deciding
a course and monitoring weather conditions, particularly on a
Chart, Bow Dividers, Parallel Rulers and Compass Rose.
Charts, the basis of
navigation, cannot be excluded from modern navigation methods.
Electronic charts that are acceptable for professional
navigation do still not cover many areas of the world. As a
result many ships are still required to carry paper charts kept
fully up to date by the navigator.
Bow Dividers can be used
in one hand and are useful for measuring distance on a chart.
The needle sharp points give precision.
Parallel Rulers – to be
used by the mariner to plot or calculate direction from the
compass rose on the Chart.
Compass Rose on a chart
has a graduated outer ring of 360 marks at 1º intervals showing
direction with respect to true north on the chart. Most have a
second ring, slightly skewed from the outer ring, showing
directions relative to magnetic north. As a journey rarely runs
north – south, planned courses rarely run through the middle of
a Compass Rose. So to transfer the courses and bearings around
the chart it is necessary to use an instrument like the Parallel
Traditional Parallel Rulers
are two straight rulers joined with pivoting arms, which allow
the rulers to be moved apart while keeping their edges parallel.
They can be walked across the chart while preserving their
alignment. They are usually of the Captain Field pattern with
the degrees marked anticlockwise.
ECDIS or Electronic Chart
Display and Information Systems
The first monitor of the Navigational Aids Simulator shows an
Electronic Chart Display. This is a most remarkable and only
recently internationally approved development in marine
navigation with many benefits for safety at sea. This system
makes it possible to plan a passage and follow it using a
computer based chart display. The monitor shows the chart with
the journey pinpointing the ship as it moves over the charted
waters. Also the Chart Information element of the system
provides the navigator with information about lights, navigation
marks and other marks of interest encountered in a passage. The
system also shows tidal heights and tidal streams adjacent to
the vessel. This information previously had to be looked up in
or calculated from one of the numerous maritime publication held
and maintained to date onboard all types of vessels.
The electronic chart system is fully integrated with the radar
on the far right and other ships and hazards can be taken from
the radar display and overlaid onto the chart for assessment of
all dangers on one display.
Our ECDIS system also includes one other elaborate radio
navigation aid….that is a computerised Navtex receiver. Navtex
is a facility provided by coastal authorised, used to broadcast
navigation warnings and weather forecasts, which, after
reception, are displayed on our electronic chart automatically.
These broadcasts are received from all over the world as well as
from the famous radio station at Valentia Island.
This overlay is not simulated, it is a real system, and so
navigation or weather warnings shown are for real!!!
Ships Controls and Sensors
The center computer screen simulates many of the instruments,
controls and sensors, which have to be monitored carefully on
the bridge of a modern ship. The ship’s course and speed can be
monitored here as well as the depth below from an echo sounder.
A Differential GPS, Loran C radio navigation receiver and a
direction finder are also simulated here and these allow the
same functionality as the real instruments calculating the
ship’s position, which is then represented on the electronic
chart. This computer also allows the navigator to control the
ships lights and siren, call for the assistance of tugs and
manually work ships mooring lines or anchors when entering or
leaving port. This computer can also access the ships steering
controls and the Autopilot set to steer an accurate course or
even a complete passage.
This console also allows the navigator to change the view of the
visual screens so that he can look astern or to either side or
even get an enhanced view using binoculars…all of the things
that are readily available to a mariner on a real vessel!!!!!
Although the ship’s speed and direction can be controlled using
the center console, all vessels have manual controls for
sensitive movements in restricted waters. The helm allows a
helmsman to steer a given course and the visual scene changes to
reflect the course chosen. Similarly the Morse throttle controls
on the main panel are used to change speed both ahead and astern
and changes in engine sounds reflect the engine revolutions
chosen. As with many large ships, engine speed can also be
adjusted using the telegraph controls on the left-hand side of
the main panel. Here the navigator rings on a speed such as
“slow ahead” and an engineer in the engineroon would respond by
changing the engine revolutions to ensure slow speed ahead.
The main panel also allows manual control of the Autopilot and,
depending on the type of ship chosen, control of bow and stern
thrusters, which permit sideways movement of the ship for
berthing and unberthing.
Direction at sea is measured using a compass – essentially an
instrument which points to magnetic north and its main axis goes
on pointing north regardless of the movement of the boat around
it. Most ships would have at least two compasses. A compass like
the one on the Simulator would be used to measure heading. This
compass is not connected to the Simulator – so the reading it is
giving is for Mizen Head. It is sitting in a ring or gimbals
that allows it to remain level whatever the swell.
Compasses make use of the fact that the earth has a magnetic
field as though a huge iron bar is embedded in its core, aligned
with its north-south axis. So any magnet that is free to swing
tends to line itself up with the earth’s magnetic field. In
marine compasses, several straight needle-like magnets or a
single circular magnet are mounted underneath a circular card
with a scale of degrees or compass points marked on it. The
whole thing is suspended in a bowl filled with a mixture of
water and alcohol, which slows the movement of the card; to
reduce the swinging that would be caused by the movement of the
Nowadays lager ships would also have a gyrocompass that uses the
properties of a gyroscope to remain aligned to True North. This
type of compass is simulated on the center controls for steering
Radar – Radio aid for detection and ranging
This instrument is simulated on the right monitor and its
purpose is to allow the navigator to detect and view other
vessels, floating hazards, land and navigation buoys. Once they
have been detected, the information can be used to assist with
navigation and help make decisions in relation to the avoidance
of collisions with other vessels or hazards.
The basic principle of radar is that it transmits pulses of
energy and measures the time that elapses before the echo of
each one returns if it has reflected off a target. Radar uses
extremely high frequency radio waves called microwaves in order
of 9.5 GHz (9500MHz) and with a wavelength of about 3cm. Radar’s
microwave pulses are focused into a beam by a rotating aerial
and transmitted horizontally through 360º around the vessel.
So radar is able to measure the range of a target from the time
it takes a microwave pulse to make the out and back trip. It can
also measure the target’s bearing from the direction that the
scanner is pointing when a pulse leaves. This information is
used to build up a picture on the display monitor, which is a
called PPI, or ‘plan position indicator’ because it looks like a
plan or a bird’s eye view of the vessel’s surroundings.
Our simulator can replicate one of three different radar models
and as with most modern radars, due to digital technology, it
can also do many of the calculations that were previously done
long hand by the navigator. All of the vessel’s course and
direction sensors, as well as our GPS position, feed into the
radar, which can then calculate the speed and course of detected
vessels automatically. This makes our simulator into an ARPA
device, more than just radar but rather an Automatic Radar
Plotting Apparatus as well as everything else. Our monitor can
also take data from real radar if required.
The ARPA can also output data for overlay onto the Electronic
Chart System to help the navigator have all the data on one
display for quick decision-making.
On the three screens is real imagery of real port scenes, which
have been turned into computer graphics. The image generation
system features real time production of marine visual scenes
with own ships, traffic ships, cultural objects, environmental
effects, visibility and illumination effects shown in full
compliance with international requirements set out for training
by the International Maritime Organisation.
An entire range of visual conditions may be displayed, showing
all variations from day, through dusk to night and from clear
visibility, through haze to thick fog, represented in any
Each ship's mathematical model incorporates an accurate movement
in 6-degrees-of-freedom. Additional sub-models are provided
which allow proper reaction of the ship to external forces such
as wind, current, sea, tugs, mooring lines and interaction with
other vessels and the environment.
Our simulator has five ship models that can be added to suit any
training requirements. The present models are, a container
vessel, a car/passenger ferry, a trawler, a stern trawler and a
rigid inflatable boat (RIB)
The Instructor Station is the key element of the simulator. It
provides the instructor with the tools and facilities for total
control over all stages of simulator operation including
generation, modification and editing of trainee exercises.
Additionally, the instructor can monitor and check trainee
performance both during an exercise and afterwards using the
debriefing facility. The passage you are now seeing on the
simulator has been recorded in real-time and is being played
back using the instructor station.