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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.
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 bouys 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 species
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 America.
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.
By:
ken jones
Article Directory: http://www.articledashboard.com
Ken Jones runs
a
Sailing Site. More information about marine electronics can be
found
here To find manufacturers or suppliers of marine electronics in
your area visit the
Marine Directory.
Best regards,
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