By Ken Jones
Autopilots The first self-steering gear was introduced in the 1920's to
control model yachts but it was not until 1948 that the principle was applied to
full scale yachts. Standing at the helm for lengthy periods, monitoring
instruments and keeping a good look out can be very tiring. An autopilot
relieves the helmsman from steering the correct course leaving him free to
maintain a proper watch. The autopilot can be set to either steer a compass
course or a course relative to the wind. A fluxgate compass or electronic wind
indicator feeds information to a microprocessor which then makes the necessary
rudder movements to return the vessel to it's required course. The mechanical
power is applied to the rudder by either electric linear activators, hydraulic
pumps or rotary drives. GPS/Chart plotters can be used to input navigational
instructions to the autopilot.
Battery Chargers will keep batteries fully charged thereby extending their
Chart Plotters Typically a chart plotter consists of an antenna, mounted high on
the boat, to track GPS signals and a display unit sited either at the at the
navigation station or the helm of the vessel. The vessels position is sent from
the antenna to the display unit which in turn shows it graphically on the chart.
The Chart itself will look similar to it's paper equivalent and show depth, land
mass, navigational aids such as buoys and potential dangers in the form of
wrecks and obstructions. The user can add way points to the chart and zoom in
and out of the display. Chart plotters can be connected to drive an autopilot
and/or send GPS data to a fish finder or radar. They can also interface with a
laptop enabling complex passage planning to be done away from the boat and then
entered into the chart plotter after arriving at the boat.
Magnetic Transmitting Compasses work like traditional compasses using magnets to
determine the vessels orientation to the earth's magnetic field they then
transmit the boats heading to an electronic display. They make steering easier
than with conventional compasses because they display steadier headings and do
not suffer from the "lag" that occurs when making a turn. They can interface
with chart plotters, autopilots and radar. Fluxgate Compasses consist of two
pieces of readily saturated magnetic material with coils wound round them in
opposing directions. AC current is passed through the coils and the material is
saturated in one direction and then the other. The earth's magnetic field
affects slightly the time at which saturation occurs, earlier in one coil and
later in the other. The difference is then calculated giving an output
proportional to the earth's magnetic field. They are accurate to 0.1 of a
degree. Their output can be displayed digitally to the helmsman or they can
interface with autopilots, chart plotters and radar.
Echo Sounders work on the same principle as sonar. A transducer emits a narrow
beam of high frequency sound. This is reflected by any solid objects and the
time between transmission and receipt of the echo is measured. The speed of
sound through water is know and so the range or distance to the sea bed can be
calculated. That is then displayed in metres. Forward Looking Sonar (FLS)
enables you to see the underwater hazards before you're actually on top of them.
A typical range for a FLS is 150 metres.
An Emergency Position Indicating Radio Beacon (EPIRB) is a piece of equipment
designed to float free of a vessel in distress. It then sends a radio signal
that can be detected by Search and Rescue Satellite Aided Tracking (SARSAT)
satellites. They relay a message to a ground station that in turn can instigate
a search and rescue operation.
Fish Finders use the same technology as sonar. A narrow beam of high frequency
sound is transmitted by a transducer, this is reflected by solid objects such as
the sea bed. By developing this technology fishfinders provide displays that
show where the fish are and they can differentiate between bait fish and larger
Global Positioning System (GPS Receivers) - This system was originally designed
for military purposes and is owned and operated by the United States Department
of Defence. 24 satellites are arranged in a "birdcage" around the globe, they
are positioned in such a way that at any place on the earth's surface a direct
line of sight can be established to a minimum of 4 satellites. A fix is obtained
by measuring accurately the distance between a satellite and the GPS receiver at
a precise time. Because the exact position of the satellite is known, these
distances provide position lines which are converted by a microprocessor within
the GPS receiver to read outs of latitude and longitude.
The log is used to measure the boats speed through the water. A paddle wheel or
impeller, mounted below the waterline is turned by the flow of water, this
generates electrical impulses that are fed to a microprocessor that displays
both speed and distance run.
Inverters - On most boats today you will find domestic equipment of one sort or
another. For on board entertainment there are televisions and stereo systems.
With the popularity of chart plotters comes the PC or laptop. Maintenance often
requires the use of power tools. Liveaboards might have a washing machine,
dishwasher or microwave. Can take 12v, 24v or 48v supply and convert it to a
stable 110 v or 220v AC supply.
Navtex can perhaps best be described as a continuously updated telex service
providing navigation and weather information within specified areas. An on board
receiver, tuned to 518kHz, the worldwide Navtex frequency, if left turned on
will either print out or display the latest massages sent from a local station.
The service is available up to 400 miles from the coast.
Radar enables you to see what otherwise would be invisible. They offer greatest
benefit at night and in fog or rain and are of particular value when close to
shore or in busy shipping lanes. They consist of an antenna and a display. The
antenna sends out a stream of RF energy which is reflected back off hard
objects. When this energy is bounced back it is converted to a signal which
displayed to the user. The antenna rotates every few seconds, the display
continuously calculates the direction of the antenna and so a precise bearing to
the target is calculated. The time is measured for the energy to be reflected
and so the distance of the target is also displayed.
Satellite Phones consist of an antenna, a modem and a normal handset. They are
powered by an iridium battery. Their range is anywhere covered by in Inmarsat
Mini-M satellite. Voice, fax, email and data can be transmitted.
Satellite TV requires an antenna and of course a television. Reception is
available within a "footprint" which is based on EIRP (Effective Isotropic
Radiated Power) of a transmitting satellite. The EUTELSAT together with the two
ASTRA satellites cover Europe. NILESAT and the two ARABSATs cover Africa and the
Middle East. Good coverage is also available in North, Central and Southern
SSB Radio has a range of several thousand miles. You will need an FFC license,
or the equivalent in whichever country you plan to operate it. Power consumption
is a consideration. Up to 100 Watts may be required for transmission. SSB radio
requires several items of equipment. A transceiver capable of SSB operation, An
antenna, this must be 8 metres long and in practice most boats use a backstay or
shroud for the purpose having fitted the necessary insulators. An antenna tuner
matched to the transceiver model. If you want to send email you will also need
and radio modem and computer.
VHF Radio The power required to transmit is minimal, all sets have the option of
transmitting on either 1 Watt or 25 Watts and the lower power should be used
whenever possible. Unlike telephones that allow you to both talk and hear at the
same time most VHF sets require you to press a transmit button prior to talking.
This is known as simplex. Duplex sets are available but are much more expensive.
VHF radio waves travel in straight lines so the aerial should be mounted as high
as possible, preferably at the masthead.
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