TOPSL RADAR DAY- DELEGATE NOTES V8

Transcription

1 TOPSL RADAR DAY TOPSL RADAR DAY- DELEGATE NOTES V8 Amended May 2012 TOPSL RADAR DAY- Delegate notes V9

2 The intention is to provide an opportunity to gain (or refresh) some knowledge and skill in the use of Yacht Radar generally. I have tried to lay this out in a logical manner, yet respecting the RYA syllabus. I hope it makes sense! Chris Williams, 07/05/2012 SOLAS COLREGS Section 1 - Conduct of vessels in any condition of visibility (Rules 4-10) Part B - Steering and sailing Section I (for any visibility) 4. Application The rules apply in any visibility (e.g. in sight or in restricted visibility). 5. Look-out Every vessel must at all times keep a proper look-out by sight (day shape or lights by eyes or visual aids), hearing (sound signal or Marine VHF radi)o and all available means (e.g.radar,ais, ARPA GMDSS.) in order to judge if risk of collision exists. 6. Safe speed Any vessel must proceed at a safe speed, which she can to take action to avoid collison and able to stop within the distance for the prevailing conditions (including the visibility,weather, traffic condition, background lights, her maneovability and draft in relation with the available water). When radar is in use, also consider if there is any limitions of the equipment, range scale in use, weather and other interference, weak targets, targets density and movement, and use radar to judge the visibility is much accurate for objects nearby. Note: Normally Fast moving vessels may have slowed down but could still be travelling very fast! It is also true that commercial pressures are probably higher than they have ever been. CHIRP reports indicate speeds of > 20 Kts are not as uncommon as they should be. 7. Risk of Collision Vessels must use all available means to determine the risk of acollision including the use of radar (if available) to get early warning of the risk of collison by radar plotting or equivalent systematic observation of detected objects.(e.g. ARPA, AIS). If the distance of any vessel is reduced and her compass bearing does not change much or a large vessel or towing vessel at close distance or if in doubt, risk of collision shall be deemed to exist. Basically, if your Yacht has Radar, you should be competent in its use. 8. Action to avoid collision Actions taken to avoid collision should be: positive obvious made in good time TOPSL RADAR DAY- Delegate notes V9 2 / 20 07/05/2012

3 Section II (for vessels in sight of one another) 11. Application The rules applys to vessels in sight of one another.(section II does not apply if in restricted visibility, see Section III) Just to amplify, the concept of Give way / Stand on vessel only applies to vessels in sight of one another. Section III (for restricted visibility) 19. Restricted visibility (a) Rule 19 applies to vessels (not in sight of one another) in or near of restricted visibility waters. (b) All ships shall reduce to a safe speed for the condition of visibility (see Rule 6). A power-driven vessel shall standby her engine for immediate use or stop (particularly for a large ocean going vessel may take long time to get her engine ready to use). (c) All ships shall comply with the Section I of this Part (e.g. Rule 5.lookout, 6.safe speed, 7.risk of collision, 8.action to avoid collision, 9. Narrow Channel & 10. TSS) for the visibility condition. (d) Take early and substantial action to avoid collision if detecting another vessel by use radar alone (not in sight), but:- 1. any change of course to port for a vessel forward of the beam should be avoided except for a vessel being overtaken (e.g. determined by radar plot), 2. any change of course toward a vessel abeam or abaft the beam should be avoided. when hearing any unknown fog signal of another vessel apparently forward should reduce the speed to minimum or make all way off (stop all water speed by astern engine) and navigate with extreme caution unless risk of collision not exist (e.g. determined by radar plot, but aware of small crafts may not able be detected or mis-identified in busy waters). Extract from Radar Manual: Until you are familiar with interpreting the radar display, you should take every opportunity to compare the radar s display patterns with visual targets, such as other vessels, buoys and coastal structures. You should practice harbour and coastal navigation during daylight and in clear weather conditions. TOPSL RADAR DAY- Delegate notes V9 3 / 20 07/05/2012

4 Basic RAdio Detection And Range Principles The terms Contact & Target seem to be used quite indiscriminately in various publications. In terms of understanding the principles, it makes no difference. Basically, the target is the object reflecting the radar energy; the contact is the blip on the screen. Scanner or antenna focuses the radio waves into a narrow beam & receives the reflected radio energy (the echo), also in a narrow beam. There are two types: radomes and open arrays. The radome has the spinning antenna inside it, so it is less likely to snag halyards, and is compact, lightweight, and has relatively low energy consumption. Open array antennas are more efficient and the larger ones offer narrower beam widths but they also have increased power demands which makes them more suitable for motorboats / ships. The transmission / reception is on the same frequency. When transmitting, the receiver is blocked. Time allocation is 99.95% Receiving, 0.05% Transmitting. Knowing the direction of the beam, using the heading mark & rotation signal, means that a target s bearing can be calculated. Knowing the time taken, using the trigger signal, for the transmission pulse to travel to the target & back means that the distance can be calculated. Radio waves travel at the speed of light (300,000 Kms / sec or 186,000 Statute miles / sec or 162,000 Nautical Miles /second). The distance calculation is more accurate than the bearing calculation due to set-up errors and / or the physical movement of the scanner mounting. Rotation Speed about 25 RPM. Approximate Values. Scanner Beam Height Beam Width Beam width at 1 Nm Beam width at 4 Nms 30 Cms (12 Inch) 25 º 8 º 250 Mts 1000 Mts 45 Cms (18 Inch) 25 º 6 º 160 Mts 768 Mts 60 Cms (24 Inch) 25 º 4 º 130 Mts 520 Mts 120 Cms (48 Inch) 25 º 1.8 º 50 Mts 230 Mts Narrower Beam widths lead to better target discrimination. (Reduces Targets merging) TOPSL RADAR DAY- Delegate notes V9 4 / 20 07/05/2012

5 Scanner &Transmitter / Receiver: The Radar uses Super High Frequency (SHF)(Microwaves). X- band Radar- 9 GHZ (9,000,000 cycles / sec) = 3 cm wavelength [All small boat radars]. S- band Radar- 4 GHZ (4,000,000 cycles / sec) = 10 cm wavelength [Some big boat radars]. Radiation danger exists close to the scanner. X band radar detects raindrops very well. S band radar energy is less attenuated by the atmosphere ( sees further but bigger scanner required.) Transmits a very short pulse of radio energy using a cavity magnetron. The cavity magnetron consists of a hot filament (the cathode) kept at or pulsed to a high negative potential by a high-voltage direct-current power supply. The initial warm up period of the Radar is exactly that. Energy reflected back (the Echo) is detected by the receiver then amplified to produce the display. The echo is very weak, more distant targets will return even weaker echoes. STC (sensitivity time control) is always function by giving more amplification to late returning (more distant) echoes. This effect is further exaggerated by the Rain control see later notes. Range: Bigger ships tend to have a bigger radar scanner, which gives a narrower beam width leading to finer target discrimination. They also have more powerful transmitters, enabling them to detect objects further away than yacht radars. Radar Shadow Radar signals cannot see through objects. A close object (Even parts of your own vessel) may cast a shadow, literally, on objects behind, which then cannot be detected. This effect may make display interpretation difficult at times. TOPSL RADAR DAY- Delegate notes V9 5 / 20 07/05/2012

6 Power Consumption: 18 Inch Scanner + Display 12 volts working & 2.2 amps on Standby. 24 Inch Scanner + Display 12 volts working & 3.0 amps on Standby. The power drain on the battery needs consideration. Display unit - displays the data received by the scanner and possibly other navigation information, depending on the set up. Navigational echoes may be large, small, bright or faint, depending not only on the size of the object but also on its orientation and surface. Different objects reflect the radar signals in different ways. The radar indication may not be similar to your visual observation; a nearby small object may appear to be the same size as a distant large object on the radar. However, with experience the approximate size of different objects can be determined by the relative size and brightness of the echoes. Buoys and small boats often resemble each other, but their motion can usually distinguish boats. Some echoes may be received from irregularities on the surface of the water, particularly at close range (sea clutter), or from rain or snow either around the vessel or in the distance. In addition, some echoes may be indirect returns to the radar scanner, providing false echoes or multiple echoes. The effects of many false echoes can be minimized, and the target presentation clarified using the controls. Practice is required to get the best information from the display. TOPSL RADAR DAY- Delegate notes V9 6 / 20 07/05/2012

7 Display Orientation Choices: Selection Purpose / Action Side Effect / Caution Head Up Basic Radar No Compass input. The radar picture is displayed with the vessel s current heading upwards. The same orientation as looking out over the bow. As the heading changes the picture will rotate. In rough weather the picture can be changing too rapidly. Possibly using Course Up might help. North Up Course Up This is most useful when trying to help the crew on deck to visually identify marks such as buoys or posts in confined waters. This is especially useful to give both you & the crew confidence in the radar picture. The radar picture is stabilised with an electronic compass input. The same orientation as the chart. North upwards. A good mode for relating chart information when away from close objects. The radar picture is stabilised with navigation input and displayed with the currently selected course upwards. Very good to help determine whether your projected track will clear a headland, for example. As you change heading, the ship s heading marker moves. Can be less a less intuitive orientation for collision prevention purposes. Swapping between North up & other Orientations when course / heading is significantly away from North will take you some time to regain your situation awareness after the picture stabilises. As you change heading, the ship s heading marker moves. If you select a new course, the picture resets to display the new course upwards. After a significant turn, it can be disorientating as it does not represent a natural view either looking ahead or chart view. TOPSL RADAR DAY- Delegate notes V9 7 / 20 07/05/2012

8 Characteristics Of the Transmission Pulse Length (PI): Length of the pulse. For long range detection, a comparatively longer pulse is helpful, however, at extremely short ranges the pulse itself must be comparatively short to aid discrimination of targets. If the pulse length is more than twice the distance between targets, the echoes will merge. The PL is adjusted by the range selection. Range Set Pulse length (PL) Distance covered by pulse 0.75 Nm 0.08us 14 Mts 7 Mts > 0.75 Nm- 6 Nm 0.25us 75 Mts 37 Mts >6 Nm 0.7us 131 Mts 65 Mts Minimum Target Separation Pulse Repetition Frequency (PRF): This is the number of pulses per second. Short ranges, high PRF, long ranges low PRF. This is adjusted by the range selection. Pulse Repetition Interval (PRI): This is the interval between pulses. The spacing between the pulses must allow for the returning pulse to arrive before the next pulse is transmitted. Short ranges, low PRI, long ranges high PRI. This is adjusted by the range selection. Side Lobes A small part of the RF energy from each transmitted pulse is radiated outside the single narrow beam. Side lobes have no effect on distant or small surface objects. However, the echo from a large object at short range may produce an arc on the radar screen similar to a range ring or a series of echoes forming a broken arc. Side-lobe echoes normally occur at ranges below 3nm, and can be reduced by adjusting the SEA control. TOPSL RADAR DAY- Delegate notes V9 8 / 20 07/05/2012

9 Radar Controls Generic Controls - Main: 1. Power On / OFF: To switch the display on, press and hold the Power key, the radar starts the magnetron warm-up sequence. 2. Transmit / Standby: After about 70 seconds, when the magnetron warm-up sequence is complete, the Standby screen is displayed, with the text Standby and a prompt to press the Power key to enter Transmit mode. To switch the radar scanner from Standby mode to Transmit mode, press the Power key. The scanner transmits pulsed energy while it rotates, and the antenna sweep builds up the radar picture using echoes returned from targets. 3. Brilliance / Contrast: adjust to suit ambient conditions. Only affects the look of the screen, not what is displayed. 4. Gain: usually Auto. Use this control for background noise (speckle). It alters the amplification of the returned pulse. Set too low, it can cause real targets to be lost. Set too high, you may not see small targets within the speckle. 5. Range: As required. Longer Range gives a better situational picture while short range provides the detail. Vary the range for optimum information. Remember that DETECTION range is not the same as selected range. Range Set Pulse length (PL) PRI PRF 0.75 Nm 0.08us 444 us 2250 Hz > 0.75 Nm- 6 Nm 0.25us 667 us 1500 Hz > 6 Nm 0.7us 1333 us 750 Hz 6. Tune: The manual setting fine tunes the receiver to the transmit frequency. In Auto mode, the radar tunes itself automatically on all range scales. Recommended to leave the TUNE control in Auto mode. If you do set the TUNE control to Manual, you will need to adjust it about 10 minutes after you have turned on the radar, since the required setting changes once the magnetron has warmed up. TOPSL RADAR DAY- Delegate notes V9 9 / 20 07/05/2012

10 Other Controls: Control Purpose / Action Side Effect / Caution Sea Clutter / To reduce the effect of waves Small targets, up to about 5 miles STC creating echoes that swamp any from the yacht may not be real target up to about 5 miles by displayed. (Sensitivity time control) regulating the gain (amplification) applied to the echoes from contacts at short range. * Could also be used to reduce side lobe effects- generally < 3 Nms. Rain (CLOSE Rain) FTC (Fast Time Constant) DISTANT Rain Does NOT Reset at Power on! To reduce the effect of rain echoes close to the yacht swamping any real target. Resets to OFF at Power on To reduce rain clutter at a distance from your vessel by altering the pulse length. This can also be used on shorter ranges to distinguish between two very close echoes on the same bearing, which may otherwise merge and appear as one echo. Resets to OFF at Power on Excessive use of rain clutter controls can weaken all contacts. When the FTC control is turned up, the receiver is less sensitive, and there is a reduction of background noise and returns from land and large targets, particularly sloping shorelines. You should therefore turn the control down when its use is not required. Interference Rejection (IR) Target Expansion Target Wakes Reduces interference from other radar sets. This usually appears as a series of small dots moving to and from the display centre in a straight line or a long, sweeping curve.. *IR can be turned off to detect the presence of other radars in the vicinity. Normally left on. To make targets easier to see by expanding them. It overrides the normal pulse length, thereby increasing the size of the target seen on the screen. The target is displayed at the brightest level and the previous positions of targets are retained at successively fainter levels on the screen. You can select long, medium or short wakes. Little / no adverse effect on displayed targets. Range resolution is diminished i.e same effect as using an over long range setting to view closer objects. Trails may obscure other useful information. Select shorter wakes to improve clarity. TOPSL RADAR DAY- Delegate notes V9 10 / 20 07/05/2012

11 Control Purpose / Action Side Effect / Caution VRM /EBL Variable Range Marker / Electronic Bearing Line A standard VRM is displayed as a circle with its centre on your vessel s position, and it s EBL is displayed as a line from the origin to the edge of the radar picture display. However, each pair can be floated, so that the origin can be moved. Note: When using VRM/EBLs, you may wish to turn off the range rings to make the VRMs clearer VRMs move if you change the range scale, so that the actual range you have marked is maintained. VRM/EBLs also move if you offset the centre. Float / (Move VRM / EBL from ships position) Offset / (Offset Centre of Display) Zoom Guard Zones To measure the range and bearing between any two points on the radar by moving the origin of a VRM/EBL away from your vessel s position and onto a target. You can then change the angle of the EBL, relative to its new origin, to obtain the bearing between two points. The radius of the VRM can also be adjusted to determine the distance between two points. Your vessel is normally at the centre of the display. The centre can be moved by up to 66% of the radius, anywhere on the screen., so that your vessel is offset. Used in conjunction with ZOOM Control. * You cannot offset the centre on the longest range. Magnifies the selected area to twice its size. The enlarged area is displayed in a quarter-screen Zoom Window in the lower right corner of the screen. Note: If the area you wish to enlarge is in the quarter of the screen that will be covered by the Zoom Window, you should offset the centre to move the area to another part of the screen before selecting Zoom. To set up sector zones or circular guard zones. Guard zones are fixed with respect to the ship s heading marker (SHM), moving as the SHM moves. They also move if you offset the centre, or if you change the range scale, so that the area you have marked is maintained. The guard alarm sounds when a big enough target enters a guard zone. Zoom Window covers part of the display. A guard zone only operates when the whole zone is displayed on the screen, or could be displayed by offsetting the centre. In addition, a guard zone is inactive for 10 seconds after it is placed or resized, to avoid inappropriate alarms during positioning. TOPSL RADAR DAY- Delegate notes V9 11 / 20 07/05/2012

12 Radar reflectors: SOLAS Regulation V/19 requires that a Radar reflector should be mounted, if practical, on al vessels. If your boat is more than 15m in length, you should be able to fit a radar reflector that meets the IMO requirements of 10m2 (*Radar Cross Section). If your boat is less than 15m in length, you should fit the largest radar reflector you can. Whatever size your boat is, the radar reflector should be fitted according to the manufacturer s instructions and as high as possible to maximise its effectiveness. *Radar Cross Section - Definition: The area of a fictitious, perfect reflector of electromagnetic waves (eg, metal sphere) that would reflect the same amount of energy back to the radar as the actual target (eg, lumpy snowflake). The Reflector: Must work for both X & S Bands Minimum performance levels specified. Mounted at least 4 metres above sea level. Still work an angle of heel of at least 20 º. Should not weigh > 5 kg. Various factors determine how well an object reflects radar pulses. Material Many yachts are made of GRP, which does not reflect radar well. Orientation Size Texture Shape Having a RADAR reflector does NOT guarantee that the yacht will appear on another ship s radar! TOPSL RADAR DAY- Delegate notes V9 12 / 20 07/05/2012

13 OTHER COMPLIMENTARY DEVICES Radar Target Enhancer (RTE): An active system that receives a radar signal then amplifies and re-transmits it. Produces a larger Blip than passive systems. 360º transmission. Small delay while being triggered may not be as effective at close range as pure reflector. Possible interference by vessels own Radar. Power consumption 150 ma Standby, 350 ma transmit. Can be fitted to activate an audible warning of radar signals. Radar Beacon -RACON Mounted on most lighthouses and other major navigational marks. Makes the return pulse longer + usually creates a Morse letter on the screen to aid identification. Typical range 10 Nm but up to 25 Nm. May not radiate on every sweep of YOUR Radar to allow echoes that might otherwise be obscured to show on the screen. Check that the Racon is consistent & within it s quoted range. Small delay while being triggered small position error. Can cause unwanted interference at short ranges reduce by rain control. Characteristics shown on chart Morse Identification e.g. Racon (W- ) (Watch out?) or Racon (U - ) YOU are standing into danger (Oil & Gas Platforms usually) or Racon (D- ) Danger -to alert new dangers Range in Nm (M) Angular Reception Sector(s) If different from the usual 360º Example Display TOPSL RADAR DAY- Delegate notes V9 13 / 20 07/05/2012

14 Search and Rescue Transponder (SART): Used in distress situations to finally locate the casualty. 9GHz receiver/transmitter. Once activated, the SART has enough power to remain in standby mode for several days. (Sea 20 SART Data). Produces a series of 12 in-line dots. (12 24 Mile scale less scale = less dots) Dots join to form rings < 1 mile to go.(the dots grow into arcs, then circles) The closest dot is the location of the SART. The trigger delay may cause an error of up to 150 metres. To improve SART reception, consider turning off the clutter suppression & the Interference Rejecter (IR). RADAR for Navigation Good for: Seeing an approaching coastline with high cliffs or buildings. Always check the chart first to determine which salient features will appear first. Running parallel to well defined high shoreline. Parallel or Cross Indexing using a floating EBL. (Must have North Up- facility) Check distance off using Range Ring / VRM. Distance / distance fixes. Measure ranges abeam first, then ahead / astern as the latter will be changing more rapidly, becoming out-of-date quicker. Bearing / bearing fixes, are not as good as distance fixes due to calibration or set up errors. Might be able to pick out river entrances or similar salient features. (see also below) RACON confirmation of position. NOT so good for: Echoes from Chalk cliffs, if dry. Low and / or Sloping shorelines should be approached with extreme caution, as the first object to show on the screen might be well inland! Small objects. Differencing between targets that are close together. (Narrow river entrance?) TOPSL RADAR DAY- Delegate notes V9 14 / 20 07/05/2012

15 Special Navigation Situations Offshore Energy Installations: There are a growing number of wind, wave & tidal energy installations in addition to the well established oil & gas platforms. The former will bring new challenges for the yachtsman. Oil/ Gas Platforms. They all have a 500m Safety / exclusion zone, protected by a radar guard zone that sets off visual & aural warnings. It is an offence to enter these Zones keep well clear. Wave / Tidal Energy Installations. These do not yet have any standard set. Just keep well clear of charted objects. Due to their diverse nature it is difficult to predict what radar return will be generated. Wind Farms. The majority of established Wind farms (as opposed to the construction phase, which may cover a prolonged period) do not have any navigation restrictions. There may be 50m exclusions around individual masts. Mast spacing is generally 500m with the lowest sweep of the rotor giving an air draft of 22m above MHWS. Due to their proliferation / footprint, it may impractical to avoid these farms completely. Radar issues: Much will depend on the angle between the blade faces & the yacht! You might expect to see a twinkling return at reasonable ranges. At closer ranges, expect radar shadows & / or very confused returns. Small vessels may be lost in the multiple returns. TOPSL RADAR DAY- Delegate notes V9 15 / 20 07/05/2012

16 RADAR for Collision avoidance Practical Strategy for Rule 19- Collision regulations 1. Keep a good mental picture of objects / traffic around using all available data / aids. 2. Use autohelm to steady the course & reduce workload.. 3. Reduce Speed & / or sailplan to minimise yacht pitching & rolling to optimise the radar picture. 4. There is no stand on or give way vessel without visual contact. 5. There is no way to tell if vessels are Constrained, Restricted or other special category without visual contact. 6. Targets that are generally moving towards the centre of the Radar screen (assuming no offset) pose a potential risk of collision. In open waters, Too close in thick fog would be < 1 mile CPA (Closest point of Approach). 7. Any manoeuvre should be made in good time. 8. The only manoeuvre mandated by Rule 19 is Slow down or Stop. 9. If no other option is remaining but to make a turn - Target in 6 o clock clockwise to 3 o clock turn to Starboard. Target in 3 o clock clockwise to 6 o clock turn to Port. Comment from Maritime CHIRP: The Board emphasises its previous advice that compliance with the Rules is sufficient in almost all circumstances and VHF conversations should be avoided. If VHF conversations are considered necessary then they should be used to confirm compliance with the Rules and not negotiate a deviation. Steps should be taken to confirm the identity of the other vessel beyond doubt TOPSL RADAR DAY- Delegate notes V9 16 / 20 07/05/2012

17 Crew Considerations: Considerations when operating in Fog or approaching an area with severely restricted visibility. Obviously the situation will determine the level of response. Off watch crew awake? All crew on deck? Lifejackets on? / Harness attached to yacht? Large torch in Cockpit ready to illuminate sail? White collision flare handy one person detailed to operate it on command? Crew briefed on developing situation / plan? Grab bag / other gear ready? [PLWF Protection, Location, Water, Food Priority order] Prepared for Mayday? Sound signals: - moving vessels. Short blast (about 1 second) Long Blast (about 4-6 Seconds) Maximum interval 2 minutes but less near other vessels. While these are the requirements, don't rely on them! Some Sound Signals for vessels underway. SOUND Code Flag / Meaning Morse TANGO Power driven vessel making way Keep clear of me (pair trawling) MIKE My vessel is stopped & making no way through the water Power driven vessel underway but stopped, not making way DELTA keep clear I am manoeuvring with difficulty None DELTA + One? HOTEL Pilot on board Vessel not under command Restricted Constrained Engaged in fishing Towing / Pushing A SAILING YACHT sailing. Vessel being towed. Last vessel if > one towed. Pilot vessel on Pilotage duties TOPSL RADAR DAY- Delegate notes V9 17 / 20 07/05/2012

18 RADAR PLOTTING: Only works if both vessels hold a steady course and speed. Use of autohelm can assist to keep your course steady, as well as reducing workload. Reduce Speed & / or sailplan while still in good visibility (see Colregs 6) to minimise yacht pitching & rolling to optimise the radar picture. In restricted waters there may be insufficient time to carry out this procedure or insufficient room to make significant alterations of course. Use Head-Up (H-up), Course-Up (C-Up) or North-Up (N-Up) display without offset. (N-Up & C Up) have stabilised pictures from compass or other inputs. Plotting Technique: 1. Plot at least 3 position of the contact at regular intervals, usually 6 minutes intervals (For ease of speed calculation). This is to establish whether the course / speed is steady. More frequent plots may be both necessary & desirable, particularly if the target is fast moving or the range at first contact is small. 2. Project the track along the line of advance. Take a tangent to the centre; this is the CPA distance. 3. To find the other vessels course & speed Plot own vessel s course & distance travelled from first to last fix. From this point join to the last fix. This represents the other vessel s relative course & speed. 4. Now you have to work out what to do! There are several other ways radar can be used to determine a risk of collision - Wakes: 1. The most basic method requires interpretation of the trails to determine whether a risk of collision might exist. Could be useful as a very early indication but not very accurate. Electronic Bearing Lines (EBL) 1. No offset on Radar. 2. Set the EBL on the target. 3. If the target continues running down the EBL then a risk of collision exists. 4. The course and speed of the other vessel is only relevant to your course and speed and is NOT, a true indication of the other vessel's true course and speed. Cursor: 1. Place the cursor over a target. 2. Plot the latitude and longitude of the target onto a chart. (This method requires the radar unit to give the latitude and longitude of the cursor displayed.) 3. Repeat at regular (6 minute? intervals). 4. Deduce the direction the target is moving and also calculate the speed of the target. 5. Now you have to work out what to do! TOPSL RADAR DAY- Delegate notes V9 18 / 20 07/05/2012

19 MARPA (Mini Automatic Radar Plotting Aid) MARPA is a function within some Radar sets used for multiple target (10 targets) tracking. Requires Manual selection of targets. Calculates target bearing and range, true speed and course Time to Closest Point of Approach (TCPA) Closes Point of Approach (CPA) Speed Over Ground (SOG) & Course Over Ground (COG) MARPA will only track targets up to a radar range scales of 12nm The status of each target can be displayed. Acquired - MARPA has lock on target Target Safe - Target will not enter defined safety zone Target is dangerous - Target will enter defined safety zone Target is lost - MARPA has lost lock on target Accuracy of ARPA is to about 250 metres and there can be several seconds delay, depending on the rotation speed of the scanner and the type of compass being used. - There are conditions where acquiring and holding a target may become difficult, these conditions are The target echo is weak. The target is very close to land, buoys or large targets The target or your own ship is making rapid manoeuvres Choppy sea state conditions exist yielding poor stability Own ship's heading data is very unstable. Inadequate heading data. AIS Automatic Identification System. These receivers are sometimes called AIS Radar. It takes two to lie, one to lie and one to listen - Homer Simpson This is not a RADAR just a receiver of VHF broadcast information. Headlands, posts, buoys or small boats do not transmit! They can appear on Radar but not on an AIS receiver. Despite the above, AIS can provide very useful information. Automatic identification systems (AISs) are designed to be capable of providing information about the ship to other ships and to coastal authorities automatically. Technical: VHF AIS1 = Mhz, AIS2 = Mhz Transmit Power = 12.5 Watts. (Compare with 1 or 25 Watts for VHF Radio) Able to set proximity Alarm. Normal VHF characteristics, line of sight range, however, it might be possible to receive AIS from a vessel in, say, in Southampton water, while still in Portsmouth Harbour. Frequency of broadcast of Basic Data (Data Update rate) depends on the vessel s activity e.g. 2 to 10 seconds while underway, and every 3 minutes while at anchor. Faster vessels broadcast more often. Only as accurate as the data being transmitted. (Real Radar is independent) TOPSL RADAR DAY- Delegate notes V9 19 / 20 07/05/2012

20 Frequency of broadcast of Additional Data is approximately every 6 minutes. The vessel can specify what additional data is broadcast. NOT Required to be fitted to: Military Vessels Cargo Vessels < 300 GRT Non sea-going Vessels anecdotally, some IOW Ferries! Despite being able to broadcast many items of information, very few ships send the full array. There are many reasons for this ranging from commercial sensitivity to piracy prevention! Don t expect to get more than position, MMSI #, basic Nav. Data (COG, SOG etc), status (Underway, anchored, Not under Command) and possibly name but it might be more. The calculation should show CPA & TCPA (Time to Closest point of approach). What AIS CAN Broadcast ( Info Only) A Class A AIS unit broadcasts the following information every 2 to 10 seconds while underway, and every 3 minutes while at anchor at a power level of 12.5 watts. The information broadcast includes: MMSI number - unique reference able identification Navigation status (as defined by the COLREGS - not only are "at anchor" and "under way using engine" currently defined, but "not under command" is also currently defined) Rate of turn - right or left, 0 to 720 degrees per minute (input from rate-of-turn indicator) Speed over ground - 1/10 knot resolution from 0 to 102 knots Position accuracy - differential GPS or other and an indication if (Receiver Autonomous Integrity Monitoring) *RAIM processing is being used If anyone wants an explanation of RAIM holes I ll answer separately! Longitude - to 1/10000 minute and Latitude - to 1/10000 minute Course over ground - relative to true north to 1/10th degree True Heading - 0 to 359 degrees derived from gyro input Time stamp - The universal time to nearest second that this information was generated In addition, the Class A AIS unit broadcasts the following information every 6 minutes: MMSI number - same unique identification used above, links the data above to described vessel IMO number - unique reference able identification (related to ship's construction) Radio call sign - international call sign assigned to vessel, often used on voice radio Name - Name of ship, 20 characters are provided Type of ship/cargo - there is a table of possibilities that are available Dimensions of ship - to nearest meter Location on ship where reference point for position reports is located Type of position fixing device - various options from differential GPS to undefined Draught of ship - 1/10 meter to 25.5 meters [note "air-draught" is not provided] Destination - 20 characters are provided Estimated time of Arrival at destination - month, day, hour, and minute in UTC Class B AIS Units (for Leisure craft) are nearly identical to the Class A, except the Class B: Has a reporting rate less than a Class A Does not transmit the vessel s IMO number or call sign Does not transmit ETA or destination Does not transmit navigational status Is only required to receive, not transmit, text safety messages Is only required to receive, not transmit, application identifiers (binary messages) Does not transmit rate of turn information Does not transmit maximum present static draught. It s greatest value is that big ships can see YOUR broadcast TOPSL RADAR DAY- Delegate notes V9 20 / 20 07/05/2012

21 1. Get own ship Steady on course & (Reduced?) Speed 2. Plot Position of Target at suitable intervals (6 mins?)[positions A, B,C] 3. Project Line through A,B,C 4. Take tangent from this line to the centre (Your vessel) 5. Position D to centre = Distance of CPA (Closest Point of Approach) The above procedure gives RELATIVE situation. To determine ACTUAL Course & speed of other Vessel 1. Plot the reciprocal of your vessels course & distance travelled from the first plot to (choose a convenient time interval) the corresponding plot. A-E 2. E-C reveals the actual direction of the other vessel. It s speed can be derived from the distance/time 3. Time to CPA, C-D, can be derived using the vessel s speed.

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