What equipment do you have on the bridge of your yacht? list 11 items
What would you have on board a yacht over 500gt less than 3000gt?
How would you know what you should have for a vessel over 500gt. Which books would you look it up in?
Magnetic compass
* Gyro compass
* Means of taking a bearing
* Echo sounder
* GPS
* Log
* Rudder angle indicator
* Radar, both 3 and 9
* ECDIS
* AIS
* Signalling lamp
* Met instruments
* Search lights
* EPRIB
* SART
* BNWAS
* LRIT
How Does Radar Work?
The Measurement of Range
using a transmitter to send out invisible, high-frequency radio waves and an antenna to receive the reflected signals, known as echoes, from objects like other vessels or land. A receiver processes these returning echoes, and a display unit translates the information into a visual image that shows the distance, direction, and presence of targets relative to the ship. The antenna constantly rotates or sweeps electronically, scanning the surrounding waters to provide a 360-degree view for navigation and collision avoidance.
The basic formula is: Distance = Speed x Time.
The electromagnetic energy is radiated in the form of a train of rectangular pulses, each of very short time duration.
How Does Radar Work?
The Measurement of Direction
Radar measures direction by using a rotating antenna to transmit a radio wave beam in a specific direction. A computer tracks the precise direction the antenna is pointing when it receives a reflected signal, known as an echo, from a target. The bearing of the echo back to the radar indicates the target’s direction, with the angle of the antenna at the time of reception defining the target’s bearing relative to the radar site
What is Pulse Length
In radar, pulse length, is the physical distance an individual radar pulse occupies in space, or the time it takes for a single pulse to be transmitted. A longer pulse contains more energy, which makes it easier to detect targets, while a shorter pulse provides better range accuracy and the ability to distinguish closely spaced targets
Energy and Detection: Longer pulses carry more energy, leading to stronger echoes and easier target detection at greater distance make it good for collision avoidance
Range Accuracy and Resolution: Shorter pulses offer greater range accuracy and the ability to “discriminate” or separate two targets that are close together on the same bearing
Carrier Frequency
X Band
S Band
Carrier frequency is the radio frequency on which the transmission is made. Marine
radar equipment is manufactured to operate in either one of two frequency bands.
‘X’ Band (3 cm) 9 GHz
‘S’ Band (10 cm) 3 GHz
Band Wavelength Frequency Application
X 3cm ~10GHz Better resolution, preferred for navigation
S 10cn ~3GHz Better in rain, longer range
What is Sea Clutter ?
Sea clutter is the unwanted radar return, or echo, from the rough surface of the sea, which can mask or interfere with the signals from actual targets, such as ships. It is caused by radar signals reflecting off ocean waves and other sea surface features. Factors like wind speed, wave height (sea state), radar frequency, and polarization significantly influence the strength and characteristics of sea clutter, making it a major challenge for radar systems to detect small targets on or near the water. Radar systems use settings like sea clutter control and filtering to reduce its impact and improve target visibility
What is rain clutter?
The rain control suppresses the reflected echoes from rain, hail and snow to clear the
display. Via video processing it does not display the leading-edge returns.
On the X-band radar, because of its short pulse length, the echoes from legitimate
contacts can become lost in the echoes from precipitation, called rain clutter. When
rain clutter masks the display, adjust this control to break up the clutter and
distinguish echoes. Adjust the control so that the clutter just disappears; too much A/C
rain action may shrink or erase the echoes from legitimate targets.
What is a Shadow Sectors
Shadow sectors are areas of reduced radar visibility (sensitivity) produced by
obstructions presenting a narrow profile when viewed from the scanner. Such objects
could well be the vessel’s own masts. The effect on the radar is similar to holding a
finger a few inches in front of one’s eyes and looking ahead. The finger obstructs the line of view, and it is not possible to see fully behind it. A mast will present a similar
problem to a radar if it is of sufficient height and width. Targets which are in line with
the scanner and the mast will be subjected to a weakened pulse due to absorption by
the obstruction or reflection from it, and provide a weakened echo return over a very
narrow sector. Because the mast will not completely block echo returns, but only
reduce their intensity, the sector provided by the mast would give rise to a narrow arc
of reduced sensitivity, known as a shadow sector.
Again, careful siting of the scanner at installation can often minimise of eliminate
these effects. On vessels having a proliferation of masts the scanner is sometimes
mounted on the foremost mast, thus giving a clear view ahead.
Detection Characteristics of Radar Targets
MAST
Material
Good conductors of electricity usually make good reflectors of radar signals. Steel is
therefore a good reflector. Wood, stone and concrete are moderately good reflectors.
Aspect
This term describes the way in which the target is presented to the radar signal.
Size
In general, the larger a target the better the chances of detection, but height is often
more important than width.
Texture
In practice any given target will be of a complex shape and may be considered as a
number of small faces all pointing in different directions – rather like a cut and
polished diamond. Only those faces which reflect the radar energy directly, or
indirectly by combination, back to the scanner will contribute to the strength of the
paint seen upon the screen. An extension of this idea helps explain the observed fact
that rough surfaced targets will almost always give better returns than smooth targets
of poor aspect.
Buildings
These are very variable in response. Large, slab sided structures have mirror-like properties and the detection may depend on the aspect. Some complex structures give good returns on all bearings. Lighthouses, however, are often very hard to detect because they give little return directly back to the scanner.
Coastal Features
The shape of the shoreline as seen on the radar screen often changes at short range as the tide changes. Mud and sand banks are usually low lying and smooth and so reflect a great deal of the radar signal away from the scanner and thus make poor targets; but watch for sea clutter from water breaking at the edge of banks which is often seen before the bank itself. Cliffs usually make very good targets because of their height and rough surface. Rising ground behind the shore line usually gives a fairly good
radar return. The steeper the better, BUT TAKE NOTE that the return from such hillsides has often been taken as if it were from the low lying beach to seaward – with disastrous results!
Errors of Radar
Must know
- Side Lobe effects
- Spurious Echoes and Effects
- Radar Interference
- Indirect Echoes
- Multiple Echoes
- Shadow Sectors
- Blind Sectors
- Radar Horizon
Setting up a Radar
Brilliance and gain should have been set to zero, so you will need to turn the brilliance up first so that the time-base trace is just visible.
Range for tuning, usually this will be one of the radars middleranges, for a 72 nm radar the 12-mile range would be selected and at the same time
check that other radar controls such as, rain clutter and interference rejection (IR) are
turned off.
**Gain **up to about 70% or until a light background speckle can just be seen. This will
ensure that weak echoes will be seen. With a raster scan display, adjust the gain up to
about 70% or until a light background speckle can just be seen, then turn it down until
the speckle just disappears.
Tune To adjust the radar, ensure you’re receiving a signal, even if it’s just sea clutter. Start with a distant, weak target and adjust the tuning knob for a clear image. If there are no targets, set the radar for maximum sea clutter.
Adjust the gain for a lightly speckled background and use the manual tuning control to maximize sea clutter. You can also use echoes from the ship’s wake during turns.
Keep all anti-clutter controls off or at minimum and use a shorter-range scale. After about 10 minutes, check the gain and retune, as the frequency may change when the equipment warms up. Recheck these settings every hour as the radar can drift out of tune.
Check that the scanner is free to rotate so as not to foul rigging and that no crew members are working in the vicinity of the scanner.
Pre-Departure Radar Checks
The performance of the radar should be checked using the Performance Monitor
before sailing and at least every four hours whilst a radar watch is being maintained.
VRM Checks against range rings, ERBL cross check against compass.
Good Radar Practice/Limitations of Radar
important
- The quality of the performance of the radar needs to be checked regularly: A performance monitor if fitted should be used for this purpose.
- Misalignment of the heading marker, even if only slightly, can lead to
dangerously misleading interpretation of potential collision situations. - Small vessels, ice and other floating objects such as containers may not be
detected by the radar. - Video processing techniques should be used with care.
- Echoes may be obscured by sea or rain clutter.
- Masts or other structural features may cause shadow or blind sectors on the display.
Misalignment of the heading marker
Heading Marker Alignment
A misaligned heading marker can cause serious errors, especially in poor visibility. Check and correct alignment regularly.
Steps:
1. Confirm the marker matches the true compass heading. 2. Compare a clear object’s visual and display bearings. Realign the marker per the manual if needed.
Do not adjust when the ship is alongside or when using unclear bearing for nearby targets.
What is Performance Monitor
The performance monitor checks the transmitter’s operation but does not indicate target detection due to atmospheric effects.
When used, a plume extends from the center of the Plan Position Indicator (PPI). The plume’s length, dependent on the echo strength from the antenna’s vicinity, reflects the transmitter and receiver’s performance and is compared to the radar’s high-performance state.
Radar Displays
- Un-stabilised means no compass input. Relative bearings.
- Stabilised means gyro fed in.
- H-up un-stabilized by any external heading input, uses that it was installedforward facing. Alterations of heading are shown by the entire image rotating away from the turn. Bearing will be relative to ships head.
- C-up display is stabilised by an external heading input, small alterations of headings are shown by the heading marker swinging side to side. Bearing can be taken relative or bearings.
- N-up image is stabilised, and it aligns with a chart or chart plotter. This is the standard setting.
- True motion and relative motion - True motion moves across the screen.
- Sea and ground stabilised. Log input.
- Sea stabilised effects of tide and wind on your vessel our accounted for anyfree floating or stationary object or moving targets will be shown with their true heading calculated via ARPA. For collision avoidance, it must be sea
stabilised. - Moving vessels have their course and speed calculated by ARPA.
- Stationary free-floating objects appear stopped.
- Anchored vessels navigation marks appear to move in the opposite direction of the combined effect of tide and current.
- Ground stabilised GPS feed in or doppler operating in BT ARPA could be wrong as it uses your course and speed to give out course and speed of other vessels. Can be used for pilotage or navigation but not collision avoidance.
How does radar measure range?
By timing return of transmitted pulses (Distance = Speed × Time).
How does radar measure direction?
By angle of scanner relative to reference (bearing).
What is pulse length?
Duration of transmitted pulse; short = fine detail, long = greater range.
What are radar frequency bands?
X-band (3 cm, ~9 GHz): Better resolution, navigation, but poor in rain.
S-band (10 cm, ~3 GHz): Better penetration in rain/fog, long range, less resolution.
What is sea clutter?
Near-range echoes from waves; reduced with STC (Sensitivity Time Constant).
What is precipitation clutter?
Echoes from rain/hail/snow; reduced with “Rain” control.
What factors affect detection?
Aspect: Orientation of target.
Size/Height: Taller targets reflect better.
Shape/Texture: Rough surfaces reflect better than smooth.
Material: Steel good; wood/concrete moderate.
Buildings/Coastal Features: Can vary – cliffs strong, mud/sand poor.
Common radar errors?
Side lobes, spurious echoes, radar interference, indirect/multiple echoes, shadow sectors, blind sectors, radar horizon.
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IRPCS42
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Buoyage61
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Flags10
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Checklist19
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Publications82
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Lights, Shapes & Sounds128
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Role of the OOW79
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Passage planning56
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Pilots16
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L.S.A179
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Compass137
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COSWP121
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Radar62
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AIS. LRIT & BNWAS39
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ECDIS61
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COLREGS143
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Chart Work46
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Position Fixes39
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Sextant34
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Fire25
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MOB30
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What is so what32
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Nav Equipment63
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Steering Systems72
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STCW51
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Radar Plotting & Arpa30
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Salvage31
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ISPS30
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LYC38
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MLC29
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MET37
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Stability61
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GMDSS31
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Medical & Rope35
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Marpol30
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ISM30
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Drive a Boat30
