The Captains F O R U M

Transcription

1 The Captains F O R U M THE HUMAN-CENTRED DESIGN FORUM In December last year, the International Maritime Organization (IMO) adopted Performance Standards and approved Guidelines the combined effect of which will be to bring about the introduction of a whole new generation of collision avoidance technology. THE relevant documents are: Revised Performance Standards for Radar Equipment Performance Standards for the Presentation of Navigation-Related Information on Shipborne Navigational Displays, and Guidelines for the Presentation of Navigation-Related Symbols, Terms and Abbreviations As the single most dramatic change concerns the integration of the Automatic Identification System (AIS) with radar and ARPA, it is probably a good idea to remind ourselves of what constitutes an AIS. AIS enables a ship or a shore-based establishment to transmit information about itself and to receive and display information from other AIS equipped ships and shore-based establishments within range. It operates primarily on two dedicated VHF Channels (AIS MHz and AIS MHz). Where these channels are not available regionally, the AIS is capable of automatically switching to alternate designated channels. The required ship reporting capacity according to the IMO Performance Standard amounts to a minimum of 2,000 time slots per minute. The International Telecommunications Union (ITU) Technical Standard for the Universal AIS provides 4,500 time slots per minute. The transmission broadcast mode used by AIS is based on a principle called (S)TDMA (Self- Organized Time Division Multiple Access), and this allows the system to be overloaded by up to 500% whilst still providing nearly 100% throughput for ships closer than 8 to 10 nautical miles to each other in a ship-toship mode. In the event of system overload, only targets far away will be subject to drop out in order to give preference to targets close by that are a primary concern for ship-to-ship operation of AIS. In practice, the capacity of the system is unlimited, allowing for a great number of ships to be accommodated at the same time. The system coverage range, as with other VHF applications, largely depends upon the height of the antenna. Its propagation is slightly better than that of radar, due to the longer wavelength, and so it is possible to see around bends and behind islands, if the Static Information MMSI (Maritime Mobile Service Identity) Call Sign and Name IMO Number Length and Beam Type of Ship Location of Position- Fixing Antenna land masses are not too high. A typical value to be expected at sea is nominally 20 nautical miles. The information transmitted by a ship s AIS falls into four categories: Fixed, or static, information, which is entered into the AIS on installation and need only be changed if the ship changes its name or undergoes a major conversion from one ship type to another; Dynamic information, which, apart from Navigational Status information, is automatically updated from the ship s sensors connected to the AIS; Voyage-related information, which might need to be manually entered and updated during the voyage; and Short, safety-related messages. Tables 1, 2, 3 and 4 provide a breakdown of the information contained in each category: Table 1 Static Information Sent By Ship Information Generation, Type & Quality Of Information Note: This might need amending if the ship changes ownership Note: This might need amending if the ship changes ownership. or if changed Selected from pre-installed list or may be changed for bi-directional vessels or those fitted with multiple antennae The Captains Forum is intended to provide those in command of a yacht with a platform to air their views on any issue as a way of enhancing the industry. If you would like to send any thoughts on the above issues for publication in the next forum, or would like to suggest topics for future consideration, please contact: captains@theyachtreport.com 2

2 Table 2 Dynamic Information Sent By Ship Dynamic Information Information Generation, Type & Quality Of Information Ship s Position with Automatically updated from the position sensor connect Accuracy Indication ed to the AIS. The accuracy indication is for better or and Integrity Status worse than 10 m. Position Time Stamp Automatically updated from the ship s main position in UTC sensor connected to the AIS. Course Over Ground Automatically updated from the ship s main position (COG) sensor connected to the AIS, if that sensor calculates COG. This information might not be available. Speed Over Ground Automatically updated from the position sensor (SOG) connected to the AIS. This information might not be available. Heading Automatically updated from the ship s heading sensor connected to the AIS. Navigational Status Navigational status information has to be manually entered by the OOW and changed as necessary; for example: under way by engines at anchor not under command (NUC) restricted in ability to manoeuvre (RIATM) moored constrained by draught aground engaged in fishing under way by sail In practice, since all these relate to the COLREGS, any change that is needed could be undertaken at the same time that the lights or shapes were changed. Rate Of Turn (ROT) Automatically updated from the ship s ROT sensor or derived from the gyro. This information might not be available. Table 3 Voyage Related Information Sent By Ship Voyage Related Information Information Generation, Type & Quality Of Information Ship s Draught To be manually entered at the start of the voyage using the maximum draught for the voyage and amended as required (e.g. result of de-ballasting prior to port entry). Hazardous Cargo (Type) To be manually entered at the start of the voyage confirming whether or not hazardous cargo is being carried, namely: DG (Dangerous Goods) HS (Harmful Substances) MP (Marine Pollutants) Indications of quantities are not required. Destination and ETA To be manually entered at the start of the voyage and kept up to date as necessary. Route Plan (Waypoints) To be manually entered at the start of the voyage, at the discretion of the master and updated when required. Table 4 Safety Related Information Sent By Ship Safety Related Information Information Generation, Type & Quality Of Information Short, Safety-related Free format short text messages would be manually Messages entered, addressed either to a specific addressee, or broadcast to all ships and shore stations. The information listed in Tables 1, 2, 3 and 4 is transmitted by the AIS at different update rates. The rate at which Dynamic information (Table 2) is transmitted is dependent upon the speed and course alteration of the ship, and this is listed in Table 5. Table 5 Report Rate Of Dynamic Information Type Of Ship Ship at anchor Ship 0 14 knots Ship 0 14 knots Ship knots Ship knots Ship >23 knots Ship >23 knots General Reporting Interval 3 minutes 12 seconds 4 seconds 6 seconds 2 seconds 3 seconds 2 seconds Static and Voyage Related information (Tables 1 and 3) is transmitted every six minutes or on request, and the AIS responds automatically to requests for information. Safety Related information (Table 4) is transmitted as required. Now we can go back to these new Performance Standards and Guidelines and analyse what they propose to achieve, bearing in mind that they will apply to radar equipment installed on or after 1 July Quoted text in italics is taken directly from the new Performance Standards. At the heart of these new Performance Standards and Guidelines lies the novel feature of AIS and radar target association. Perhaps the best way to explain this is to imagine two separate, but identical, display units side by side on your bridge. One would be displaying the positions (targets) of other vessels as determined independently by your own radar system. The other would be displaying the positions (targets) of other vessels in accordance with the dynamic data (Table 2) taken from their respective AIS messages. Placing both radar and AIS targets on one display would very probably lead to a situation where, in many cases, a radar target symbol and an AIS target symbol overlapped either completely or partially. At best, the picture would be cluttered and untidy, and, at worst, it would be downright confusing. AIS and radar target association is based upon the principle of comparing the position and movement of a radar target with the 3

3 position and movement of an AIS target and then deciding whether or not those targets could be considered as representing the same physical object. If they could, it would then be possible to display just one symbol instead of two and to make available both radar tracking and AIS data, in an alphanumeric format, for that single symbol. It is important to emphasise at this stage that association will only apply to radar targets that are being tracked. In other words, you will have to either manually acquire a radar target for tracking or configure your system to automatically acquire and track it. Table 6 details the new requirements for acquired radar target capacity and for auto acquisition of targets. No information exists, as yet, as to precisely how technology will be used to there is always a real danger that a design default condition becomes accepted as being the standard or normal condition. Are you happy with this development? Do you want a system that will be designed to show you, as a default condition, the activated AIS target symbol and the alphanumeric AIS target data when you are actively considering, or conducting, collision avoidance? The expression activated AIS target brings us to the next significant feature of these new Performance Standards, whereby AIS targets are deemed to be either sleeping or activated. Tables 7 and 8 list and describe the various tracked radar and AIS target symbols specified in the new Guidelines. It is easy to see from Table 8 that a large number of activated AIS target symbols on a display could easily lead to a problem with clutter. The much simpler and smaller sleeping AIS target symbol has been developed to attempt to overcome this problem, and the new Performance Standards state that: AIS targets that are displayed should be presented as sleeping targets by default. Table 6 details the minimum capacity requirements for activated and sleeping AIS targets. The use of the term sleeping is, perhaps, unfortunate, as it implies a state of rest, when, of course, a sleeping AIS target is no less real and no less mobile than an activated one. The difference is all to do with data presentation and with the functional options available within the overall radar/arpa/ais system. Those of you who are familiar with operating modern radar/arpa systems will be Table 6 Differences In The Performance Requirements For Various Sizes/Categories Of Ship/ Craft To Which SOLAS Applies Size Of Ship/Craft <500 gt 500 gt to <10,000 gt All Ships/Craft and HSC<10,000 gt 10,000 gt Minimum operational display area diameter 180 mm 250 mm 320 mm Minimum display area 195 x 195 mm 270 x 270 mm 340 x 340 mm Auto acquisition of targets - - Yes Minimum acquired radar target capacity Minimum activated AIS target capacity Minimum sleeping AIS target capacity Trial Manoeuvre - - Yes decide when a tracked radar target and an AIS target will be the subject of association. The new Performance Standards talk in terms of an automatic target association function based on harmonized criteria. Notably, however, they make it absolutely clear that If the target data from AIS and radar tracking are both available and if the association criteria (e.g. position, motion) are fulfilled such that the AIS and radar information are considered as one physical target, then as a default condition, the activated AIS target symbol and the alphanumeric AIS target data should be automatically selected and displayed. This leaves the distinct impression that, with regard to collision avoidance, the IMO is saying that AIS data is considered to be more accurate, more reliable and more useful than tracked radar data. To be fair, the new Performance Standards go on to say that: The user should have the option to change the default condition to the display of tracked radar targets and should be permitted to select either radar tracking or AIS alphanumeric data, but Table 7 Tracked Radar Symbols Topic Symbol Description Tracked inc. Dangerous in Acquisition State Lost Selected Past Positions Solid filled or unfilled circle located at target position. The course and speed vector should be displayed as dashed line, with short dashes and spaces approximately twice the line width. Optionally, time increments, may be marked along the vector. For a Dangerous, bold, red (on colour display) solid circle with course and speed vector, flashing until acknowledged. Circle segments in the acquired target state. For automatic acquisition, bold circle segments, flashing and red (on colour display) until acknowledged. Bold lines across the circle, flashing until acknowledged. A square indicated by its corners centred around the target symbol. Dots, equally spaced by time. Tracked Large R adjacent to designated tracked target. Reference Multiple reference targets should be marked as R1, R2, R3, etc. 4

4 Table 8 AIS Symbols Topic Symbol Description AIS An isosceles, acute-angled triangle should be used. (sleeping) The triangle should be oriented by heading, or COG if heading missing. The reported position should be located at centre and half the height of the triangle. The symbol of the sleeping target should be smaller than that of the activated target. Activated AIS An isosceles, acute-angled triangle should be used. The triangle should be oriented by heading, or COG if Including heading missing. The reported position should be Dangerous located at centre and half the height of the triangle. The COG/SOG vector should be displayed as a dashed line with short dashes with spaces approximately twice the line width. Optionally, time increments may be marked along the vector. The heading should be displayed as a solid line thinner than speed vector line style, length twice of the length of the triangle symbol. Origin of the heading line is the apex of the triangle. The turn should be indicated by a flag of fixed length added to the heading line. A path predictor may be provided as curved vector. For a Dangerous AIS, bold, red (on colour display) solid triangle with course and speed vector, flashing until acknowledged. AIS A true scale outline may be added to the triangle True Scale symbol. It should be: Outline Located relative to reported position and according to reported position offsets, beam and length. Oriented along target s heading. Used on low ranges/large scales. Selected A square indicated by its corners should be drawn around the activated target symbol. Lost Triangle with bold solid cross. The triangle should be oriented per last known value. The cross should have a fixed orientation. The symbol should flash until acknowledged. The target should be displayed without vector, heading and rate of turn indication. Past Dots, equally spaced by time. Positions only too aware of the number of functional options already available to you. The addition of AIS will certainly add to that number, but, much more importantly, it will present manufacturers with a massive challenge to ensure that their systems do not incorporate features that may lead users to make errors, not detect errors, or recover too late from errors that may have serious safety consequences. The new Performance Standards address the following seven major functions, and associated presentational issues, relating to how you, the user, may choose to employ AIS data: You will have no control over AIS data processing, which presumably will be going on continuously in the background. However, you will have the option to switch the graphical presentation i.e. the AIS target symbology either ON or OFF. Your choice of function will be presented to you by either alphanumeric or graphical means. If you have chosen to switch the function ON, then AIS targets will be displayed with their appropriate symbols, and, if you then select an activated AIS target, the following data will be presented to you in alphanumeric format: source of data, ship s identification, position and its quality, calculated range of target, calculated bearing of target, CPA, TCPA, COG, SOG, navigational status, ship s heading and rate of turn. Additional target information will be provided on request. The new Performance Standards do not specify what this additional information will be, but presumably it will be the information listed in Tables 1, 3 and 4. If the received AIS information is incomplete, then the missing information will be clearly indicated as such. Data displayed for an activated AIS target that you have selected will be continually updated until you either select another activated AIS target or close the data window. You will be able to filter out sleeping AIS targets so as to ensure that the clarity of the total presentation is not substantially impaired. The way that you will be able to do this is not specified, but the following examples are given: by target range, CPA/TCPA or AIS target class A/B. If you choose to employ this filter function, then there will be a clear and permanent indication to this effect, and the filter criteria that you employ will be readily available to you. All this information may be presented to you using either alphanumeric or graphical means. Incidentally, you will not be allowed to remove individual AIS targets from the display. A means to activate a sleeping AIS target and to deactivate an activated AIS target will be provided. Presumably this is meant to be a manual function for activating/deactivating individual AIS targets, but the new Performance Standards are silent on this matter. However, zones for the automatic activation of AIS targets may be provided. If they are, they will not differ from any zones that may be provided for automatic radar target acquisition. You will be able to define these zones, and they will be presented in graphical form on your display. Presumably, although this is not specified, the functional inputs that you make to define and activate these zones will be readily available to you so that you can check what you have set and change the criteria as necessary. Thus the intent appears to be that, if zones for the automatic activation of AIS targets are provided, the symbol of any sleeping AIS target infringing one or more zones that you have selected and defined will automatically change to an activated AIS target symbol, and an alarm will sound. You may have the option to ensure that sleeping AIS targets are automatically activated if they meet parameters that you will be able to define. These parameters are not specified, but the following examples are given: target range, CPA/TCPA or AIS target class A/B. If you choose to operate this 5

5 function, then there will be a graphical presentation to that effect, but there are no details as to the form that this will take. Presumably, although this is not specified, the functional inputs that you make to activate these parameters will be readily available to you so that you can check what you have set and change the criteria as necessary. Thus the intent appears to be that, if this option is available, the symbol of any sleeping AIS target infringing the parameter(s) that you have defined will automatically change to an activated AIS target symbol. If an activated AIS target infringes CPA/TCPA criteria that you have defined, then its symbol will change to a dangerous AIS target symbol, and an alarm will sound. You will, however, have the option to turn the alarm function either ON or OFF. It is not clear as to whether the OFF option just applies to the alarm sound or whether it also applies to the dangerous AIS target symbol. Nevertheless, you will be provided with a clear indication of the status of the alarms and of the alarm criteria. However, there are no details as to the form that this indication will take. You will also have the option to apply this entire function to sleeping AIS targets. You will not be able to define separate CPA/TCPA criteria for tracked radar targets and activated AIS targets. Whatever criteria you choose will apply equally to both types of target, and, as a default, the CPA/TCPA criteria that you have selected for tracked radar targets will be applied to all activated AIS targets. Presumably, although this is not specified, the CPA/TCPA criteria that you define will be readily available to you so that you can check what you have set and change the criteria as necessary. You will have the option to enable or to disable a lost target alarm function for AIS targets, and there will be a clear indication to this effect, although there are no details as to the form that this indication will take other than it will be alphanumeric or graphical. If this function is enabled and if unspecified lost target filter criteria are met, then the last known position of an AIS target for which no data had been received for a set time will be marked by a lost target symbol (Table 8), and an alarm will sound. Whether or not you will be required to define the lost target filter criteria and/or the set time is not clear, but, if you are, then presumably the inputs that you make will be readily available to you so that you can check what you have set and change the criteria as necessary. You will have the option to enable or to 6 disable the target association function. If you choose to select it ON, then, as stated earlier, whenever an association takes place, the system default, by design, will be to select and display an activated AIS target symbol (Table 8) and also to display the relevant alphanumeric data for that AIS target. If this alphanumeric data is going to be displayed in some sort of window, then a difficult presentational problem could arise if a number of associations occurred in rapid succession, for example, in a busy shipping area. The new Performance Standards are silent as to whether or not you will have any input to the association criteria. However, you will have the option to change the default to the display of tracked radar targets. If you choose to select this mode, it is not clear as to whether or not there will be any indication that a tracked radar target is the subject of association. Presumably, your choice of default mode will be clearly indicated to you. Whilst it is obvious that much of the functionality currently available for radar tracking, for example acquisition/activation zones and CPA/TCPA, has been employed in an identical fashion for AIS, there is, nevertheless, a significant increase in the overall functionality prescribed by the new Performance Standards. More importantly, there has been a quantum shift in emphasis in value from radar target data to AIS target data. Is this what you want? When considering your answer, it is important to note that the new Performance Standards will also permit the radar display to incorporate vector chart information, that is elements of an ECDIS, and/or map graphics, together with the ability to configure a user selected (task orientated) presentation. This will enable you to configure a presentation for a specific task at hand. Such a presentation may include radar and/or chart information, in combination with other navigation or ship related data, and, when not fully compliant with the radar or ECDIS performance standards, it will be identified as an auxiliary presentation. It would appear that, with regard to auxiliary presentations, the intent is to ensure that, as far as practical, the presentation of any radar and/or ECDIS related functions will be compliant with the requirements of the relevant performance and presentation standards. However, the size of the operational area may be reduced, enabling chartlets, or windows of radar information, to be presented along with other information associated with the task at hand. Such a potentially complex system will undoubtedly require very careful management by you, the user. Your comments relating to the subject matter of this article would be most welcome. In particular, we would like to know what you consider to be the role of AIS in collision avoidance. Please address your comments to: captains@theyachtreport.com Now is the time to make your views known as the International Electrotechnical Commission (IEC) has yet to complete the technical standards that will determine how these new IMO Performance Standards will be translated into system type-approval criteria. Paul Wood Marine Navigation Consultant Look Out! Paul Wood Associates Ltd