ADVANCES IN NAVlGATlO N

Digital charting: a Royal Navy navigator‘s view

M.A. Hadley

Indexing terms: Digital hydrographics, Hytlrogruphic charts, Hydrographic displays, Nuvigulion

Abstract: The IMO have recently given their approval to the concept of an electronic chart display and information system (ECDIS) (IMO Assembly resolution A.817( 19)) but the detailed technical specification required for Type Approval is still to be completed. Meanwhile, the approved ‘vector data’ required for ECDlS is only just beginning to be available and its form is still evolving. The Royal Navy is moving towards adoption of this new technology and has mandated its use for a future class of frigate. It is already involved in trials of prototype equipments, albeit using a (raster) data forinat which has yet to receive international approval. Trials supported by UK manufacturers and the UK Hydrographic Office are proving beneficial to all involved and vector data will be incorporated during 1996. The need to strike a balance between adapting current navigation techniques to the electronic era and devising new ones has already been recognised, as is the inevitable impact on training. The ability to measure positions, bearings and distances far more accurately than ever before is putting the hydrographers on their mettle, while the need to understand and correctly apply datum shifts and match projections when displaying different forms of data is posing a new challenge for thc navigator. The end of the paper chart in the RN may be forecastable but is not yet in sight and there are a number of questions that need to be resolved before ECDIS becomes accepted as the prime method of navigation.

1 Introduction

This paper precedes the outcome of a reassessment c navigation policy in the Royal Navy (RN) and so the views expressed can only be those of the author.

The R N is increasingly interested in the concept of digital charting, although this is motivated by some- what different factors to those of commerce where, in

0 IEE, 1997 IEE Proceedings online no. 19971236 Paper first received 21st December 1995 and in revised form 3rd October 1996 The author was with MOD Portsdown, Portsmouth and is now with the Maritime Navigation Systems Group, DRA Fraser, Fort Cumberland Road, Eastney, Portsmouth, Hants PO4 9LJ, UK

some quarters, there is still a drive towards one-man bridge operations (OMBO). A warship rarely goes from A to B by the most direct route at a constant speed and the R N has no aim to achieve one-man bridge operation. However, it is already RN practice to man a frigate’s bridge with only two men, the Officer of the Watch (OOW) and the Quartermaster (QM), when on passage or in a cruising watch, although an Officer Under Training may also be present. This reduction, from a previous norm of four or five men, has been coupled with an increase in the information which the OOW has to absorb; a trend which will con- tinue for the foreseeable future. In consequence, some- thing needs to be done to ease the bridge team’s workload if the ability of the OOW to maintain ‘a good lookout’ is not to be degraded. Several measures involving bridge design, the use of multifunction dis- plays to display the large amounts of secondary data required and a greater degree of automated recording are being investigated. However, the greatest single fac- tor which will ease the OOW’s workload is the combi- nation of an electronic chart display and information system (ECDIS), an International Maritime Organisa- tion (IMO) type-approved radar automatic radar plot- ting aid (ARPA), and an accurately derived and automatically displayed ship’s position, such as that provided by the Precise Positioning Service of the Glo- bal Positioning System (PPS GPS). Use of such a com- bination may mean that, when on passage, the operations room crew can be dispensed with. In addi- tion to navigation, the RN has an increasing need for digital geographic data in its shipboard combat systems and associated land based command and control sys- tems; this necessarily includes digital hydrographic data.

Although the technology to display charts in digital form has been available for some time and has already been demonstrated and used at sea, the decision to move to the use of an electronic chart (EC) is, quite rightly, being challenged on the grounds of cost, man- power savings and operational requirement. However, with the IMO having only just decided what constitutes an ECDIS and with agreement on the technical details of the specification for an IMO type-approved ECDIS probably some two years away there is no need for haste. Certainly the R N will only buy type-approved equipment which can be considered to be legally equiv- alent to the paper chart and which uses data either pro- duced, or at least approved of, by the UK Hydrographic Office (HO). ECDIS is only currently authorised to use vector data in the International Hydrographic Organisation’s (IHO) S-57 format of

143 IEE Pror -Ruduur, Sonor Navir., Vol. 144, No. 3. June 19‘17

which there is very little available, although its produc- tion in the UK is being stepped up. With this in mind, the first new class of ship to be fitted with an ECDIS is likely to be the Common New Generation Frigate, which is a tripartite development involving France, Italy and the UK, delivery of which is planned early next century. The equipment, in its military form, has been named Warship ECDIS (WECDIS).

2 Information System (WECDIS)

Although WECDlS will be based on commercial off- the-shelf equipment and be compliant with the rules governing ECDIS it will also have to incorporate sev- eral additional features if it is to meet the military requirement. Perhaps the most significant of these will be the need to handle classified military navigational data and, because an availability date for worldwide vector data coverage cannot be predicted, the need to handle raster data. WECDIS will also have to interface with the ship’s combat system, specifically the combat management system, which will incorporate near real- time staff planning tools including the ability to plan navigation.

2. I Data standards There is no internationally agreed standard for raster chart data but considerable work in producing this type of data has already been done by the HO, in col- laboration with the UK equipment manufacturers Kelvin Hughes and Racal Decca. The result has been the Admiralty Raster Chart Service (ARCS), first announced in November 1993 and for which a world- wide outfit of charts is expected to be available by the end of 1996. Two naval trials of ARCS products are

Warship Electronic Chart Display and

currently underway in HMS Slzejfield and HMS Bull- dog and a third, which will also include the use of WO and commercially produced vector data, is underway in RFA Black Rover. The trial in HMS Shejjield has been extended to include HO vector data and HMS Illustri- ous will be taking an ECDIS on her deployment later in the year. Results so far are extremely encouraging and it is already apparent that the raster chart display, coupled with the use of overlays, is capable of approaching the user’s requirement for vector data and offers significant advantages over the use of the exist- ing paper chart. However, the true benefit comes from interfacing the system with an accurate navigation aid, such as PPS GPS and an I-band radar with ARPA. This provides the capability to continuously display the ship’s position with respect to the planned track and ARPA track data in its geographic context. The latter feature may allow an intelligent assessment concerning the type of vessel that a radar contact represents as well as sensible predictions about its future movements to be made. This will complement any data available from the proposed automatic identification system on ships (AIS).

2.2 Potential for fit and retrofit What has been confirmed by the R N trials, and is already being offered by manufacturers, is that the ECDIS (WECDIS) display and the ARPA display must be sited side by side at the bridge front and be capable of being used by a forward-facing operator. This ‘blinding glimpse of the obvious’ is mentioned only because it has a direct bearing on any plans to ret- rofit WECDIS in existing ships. Warship bridges range in size from that of a minehunter (approximately 20m2), via a frigate/destroyer (approximately 30-35m2),

bridge wing

Fig. 1 BM CMD DIMPS

% oow NO QM

144

Schemutic bridge 112yO71t o j Type 23 frigate cftwfitting u fi,rward-fucing chart table and nuvigation radar disp1u.y Boatswain’s Mate SHOLIS Ship’s helicopter operating limits inlbrmalion system Command SNAPS Ship’s navigation and plotting system (chart table) Automatcd message handling system TCD Tactical communications director (Yeoman) Miniature radar display Tor Command use TO Tactical operator Radar display Tor the X-hand radar 1006 VCS Versatile console system OTficcr of the Watch 778 Echo sounder Navigating Oi’ficer 1008 S-band navigation radar Quartermaster

IEE Pro.-Rudur. Sonur Nuvig , Vol. 144, No 3, June I997

to an aircraft carrier (approximately 43m2). These sizes are almost inevitably smaller than their commercial counterparts while being expected to contain additional equipment and systems not found in a merchant ship. In consequence, the bridges of existing RN ships are already quite ’full’ and, in particular. there is alniost no free space at the bridge front. Thus, to accommodate two new. relatively large displays side by side, all cur- rent RN bridges will require modification, some to a considerable degree. Although a study into the pro- jected costs of retrofitting WECDIS is currently under- way, it is reasonable to suppose that the cost of buying the WECDIS, and where iiecessary an ARPA display, will be dwarfed by the ship-fitting costs. These costs, when taken with thc fitting opportunities available for individual ships, are likely to dictate which ships will be retrofitted with WECDIS. Fig. I , which shows a pro- posal for the fitting of a forward-facing chart table in a Type 23 frigate, gives an indication of the scope of the work and hence the costs which could be involved in fitting WECDIS and its associated equipments to a warship’s bridge.

Proposed requirements for WECDIS call for two bridge chart displays, one sited at the bridge front for use by the OOW with sufficient capability to monitor the ship’s position with respect to the planned track, and a second towards the rear of the bridge, capable of both monitoring and planning navigation. Trials involving only a single electronic chart display have shown the merit of providing two displays in ships, especially those with variable display capabilities; cur- rent IMO guidelines and some existing systems do not allow the editing of a navigation plan in use. However, it is clear that some RN bridges will not provide suffi- cient space for two WECDIS displays and considera- tion will have to be given to siting the second (planning) display in the charthouse.

2.3 Effects on manpower Although not considered to be a prime reason for the RN buying a WECDIS the effects on manpower requirements have to be considered. The most obvious reduction will be in the manpower needed to correct papcr charts and, eventually, navigation publications. However, the days of a dedicated navigator’s yeoman are past, thus the prospective reduction will only be on the part-time employment of one sailor. Even this small reduction needs to be set against the ship’s overall manning requirement for operations and will be hard to quantify. In any case, there is likely to be a continu- ing requirement for at least some paper charts and publications plus navigation equipment requiring main- tenance. One significant benefit, however, will be that the correction process will be both swifter and more accurate than today and, with the aid of satellite com- muiiica tions, potentially instantaneous.

2.4 Future for paper charts The continuing need for paper charts comes from two specific directions. The first is currcnt legislation, which has been interpreted as stating that the raster chart is not equivalent to the paper chart. The second is the need to provide for ECDIS failure. The first reason will entail an increase in OOW workload, if ECDIS is to be used for navigation in conjunction with the paper chart. This is patently an unsatisfactory state of affairs and it is to be hoped that the [MO will recognise the

IEB P w . - U u d a i , Soniir Ni~vig, Vol. 144, No 3, June 1997

mismatch between, on the one hand, the eagerness of users to employ and the manufacturers to sell ECDlS and, on the other, the reluctance of those sanctioning the purchase of ECDIS because they can see no direct financial or operational benefit. until vector data is more freely available. This will, hopefully, result in swift action to ‘legalise’ raster data. The second point is not so clear cut because various alternative solutions, such as the use of a laptop, are possible. However, it seems realistic to suppose that a paper chart, in some form. will be required for the foreseeable future. For this reason, i t is anticipated that the overall specifica- tion for WECDIS will also include a printer. Although the JMO, in its wisdom, may demand a second, totally independent ECDlS as the only safe back-up for a fail- ure of the first ECDIS.

2.5 Need for vector data The desire for recognition of a raster standard should not be taken as in any way detracting from the ulti- inate goal of employing vector data. In the short-to- medium term, raster and vector data are seen as com- plementary and it i s foreseen that dual capable systems (hybrids) will be required until full vector data cover- age is available. Trials indicate that raster data can bcgin to approach the user’s requirement for an ECDIS but that it cannot offer the seamless, layercd and dynamic qualities provided by vector data. The layer- ing aspect is particularly relevant to a warship where some hydrographic data. such as coastline, a particular depth contour or wreck data inay be of crucial impor- tance to operations. However, such data is only of practical use if it i s capable of precise selection so that the operator’s display, already ‘busy’ with sensor and other tactical data. is not swamped. When using raster chart data, an opcrator sees either all the chart detail or none of it and when it is ‘zoomed out’ the detail quickly beconies unreadable and the screen far too busy.

2.6 WECDIS and radar This leads to the current, occasionally passionate debate about the advisability of superimposing radar data on ECDIS, or vire vc‘rLsu. There is potential benefit in bcing able to add ‘picture matching’ to the naviga- tor’s position-finding armoury, although height of tide and distance offshore will affect accuracy. Set against this is the undoubted potential for radar clutter in addition to the sheer weight of the combined data pre- sented to the operator to degrade the picture. These two points can be dealt with by allowing the operator to choose when to superimpose the two pictures, or the use of interlaying, and by the provision of a single action operation to return the display to its prime state. Future devclopments in track extraction techniques will also reduce the impact of clutter on the operator’s dis- play. What is less easy to decidc is whether it is right to allow the display of ground stabilised radar data, where the motion of all tracks will be seen ‘over the ground’ and judgement of aspect likely to be made accordingly. The International Rules for the Prevention of Collision at Sea are based on the true aspect one ship preseiits to another. which when not readily seen is judged by another ship’s track through the water as seen on a nonground stabilised (i.e. sea stabilised) radar display. Both methods of display have their use and the operator must recognise their strengths and

145

weaknesses. In restricted visibility, it would seem sensi- ble io continue to base decisions on anticollision inat- ters on ARPA data but with due regard to any geographic constraints, which are best judged from viewing the ARPA track data displayed on the chart. The RN will be in a better position to take a view when the results of its trials are known but it is inter- esting to note that guidance on this point is already contained in the standing instructions of at least one major UK shipping company.

2.7 Training The impact of fitting WECDIS on training in the RN is still being assessed but it is bound to be significant. Certain ships will continue to use only paper charts until they are decommissioned, overlapping with those newly commissioned, thus preventing a clean break between training for traditional navigation methods and those needed for WECDIS. In any case, depending on what is finally decided about the reversionary method of navigation in a WECDIS fitted ship, there is a possibility that there will be a continuing need for the traditional methods of navigation, using visual and radar fixing techniques, to be taught at all levels of shore training and maintained at sea.

2.8 General navigation The trials of ECS have served to emphasise the impor- tance of developing user friendly methods of inputting visual and radar fix data, by no means a trivial task, and thoughts are already turning to ways in which bearings can be ‘cut through’ from azimuth repeaters and ranges from the radar. Given the problems of waterproofing such a system the possibility of using voice recognition techniques is also being explored. Other sources of range and/or bearing data are likely to be available from laser, electro-optic and infrared sys- tems. Where the nature of the seabed allows, access to a WECDIS will ease the establishing of position by means of running fixes based on crossing depth con- tours and spot depths. I n addition, WECDIS offers the prospect of linking the integrated navigation system and the autopilot to permit automatic track following as opposed to today’s course following. This will, in turn, allow the use of track-following alarms.

3 Navigation

3. I Pilotage More interesting decisions are in prospect about how pilotage (in RN terms ‘navigation in confined waters’) is to be conducted. The current practice is for the Nav- igation Officer (NO), having previously prepared his plan in detail, to conduct the ship’s navigation from the pelorus using the data captured in his notebook. The ship’s position is checked by both visual means using the bridge chart and by the Blind Pilotage Safety Officer (BPSO) using radar blind pilotage techniques in the operations room. The BPSO’s radar solution is also checked by the plotting of radar fixes on a chart in the operations room. The overall result should be that the Command hears three, hopefully coincident, reports of where the ship is and what it is required to do; any divergence in the reports is immediately apparent. In addition, a constant watch is maintained on the echo sounder, comparing its readings with the minimum expected depths calculated by the NO and BPSO. There is no need for this concept of a three-tier system

146

of navigation to change, although the checking of the NO’S solution should now be by means of a PPS GPSi DGPS position displayed on the WECDIS in real time and there is the potential for automatic depth alerts and the provision of an automatic process to warn against the ship crossing a predetermined ‘no-go’ line. The BPSO’s blind pilotage solution could also be checked by plotting radar fixes on the WECDIS. How- ever, this latter check may be more economically achieved using the output from a printer rather than by the use of an operations room WECDIS display, as the remaining geographic data requirements of the warfare team will be met by other elements of the combat sys- tem. Potentially, in WECDIS, the R N will have the ability to conduct pilotage in adverse weather condi- tions in complete safety, which can only improve its military capability.

3.2 Blind pilotage The fitting of WECDIS will, for the first time, permit two truly independent methods of navigation in restricted visibility. With the accuracy now available from PPS GPS, which is likely to improve further, it is expected that the prime method of navigation in restricted visibility will be by means of WECDIS, sup- ported by radar. Present blind pilotage techniques using radar parallel indices will remain available to the BPSO and as a reversionary method to the NO should WECDIS fail.

3.3 Effect on navigation methods There is a natural inclination to adapt this new tech- nology to present navigation techniques and the speci- fier of the user’s requirements for WECDIS must retain an open mind as to how the opportunities WECDIS presents can best be exploited. For instance, should the R N continue to insist whenever possible on pilotage in unrestricied visibility being based on the use of head/ stern marks, with safety being judged by means of clearing bearings and distances to whecl-over points checked by beam marks? Would it perhaps be more practical to take advantage of an enhanced accuracy PPS GPS and simply use WECDIS instead? Trials have indicated that new methods of pilotage are feasible and work is already in hand to write a new chapter for the Admiralty Manual of Navigation. It is easy to see how the answer to my question might be ‘Yes’ in a situation where a ship’s operations could be limited to an area completely covered by vector data and where a success- tu1 tidal model had been incorporated to make the chart data dynamic. It is also noticeable that using a ‘no-go’ line drawn on an electronic chart affords more safe water to the ship handler than the use of clearing bearings on a paper chart. However, underpinning all thoughts about these types of question is the require- ment for the R N to be capable of worldwide opera- tions, if necessary in hostile conditions which may preclude use of any given navigation aid. If, as seems likely, the traditional pilotage and navigation methods will be retained the question arises of how the neces- sary skills are to be maintained? In a ship where the norm may be the use of WECDIS, the NO/OOW may be required to change to the use of traditional tech- niques at a momcnts notice and with the ship already committed to confined waters. Will the changeover be fluent‘? This is an important reminder of the signifi- cance of training, although in this case it is of the con- tinuation rather than basic variety.

IEE Proc.-Racior, Soniir Niivig., Vi11 144, No. 3, .June IVY7

3.4 Positional accuracy and charting considerations The RN’s WECDIS will be based on ECDIS and the need to specify the system’s requirements is largely one of specifying the W part. There is an underlying assumption that the normal navigation data as used by all seafarers will be available. Currently this cannot be taken for granted as the various members of the IHO negotiate with each other about whether hydrographic data in S-51 format can be exchanged and if so under what conditions. However, in seeking to satisfy the additional military requirements some interesting chal- lenges have arisen. Some or all of the hydrographic data used by WECDIS will also be required by other parts of the combat system. How are the needs of a number of systems within a ship to be met most eco- nomically, bearing in mind the inherent problems caused by data redundancy and the regular require- ment to update hydrographic data? It is a fact that ‘land mappers’ and ‘sea charters’ use different datums and different data formats. As it is impractical to expect either discipline to adopt the other’s standards, how is the data to be merged? This is not so important for WECDIS but it is a serious consideration for the combat system of ships, particularly those engaged in amphibious operations.

Sadly not all paper charts are suitable for ‘vectoring’ and the area covered by some will require to be resur- veyed, a principle reason for the length of time it will take before world coverage can be achieved. However, when in vector form all charts will be referenced to WGSX4 (or its approved successor). Using raster charts a prime consideration is the chart’s datum/spheroid. Where this data is known, algorithms are available to make the necessary transformation. However, what is the effect on the user when the datumhpheroid is not known, which is the case for approximately 50% of the HO’s charts? Manufacturers are having to cope with this problem but, given that errors cannot be quanti- fied, the user must be clear what is being done to the chart data (or the positional data in use). Another problem, how to deal with chart data which is skewed such that a uniform transformation cannot be applied, has been resolved by the breakdown of the area cov- ered by the chart into tiles of a size where a uniform transformation is possible. Trials have already revealed a need to consider incorporating the capability to change a ‘known’ transformation’s parameters, where the user detects that the one in use is incorrect. Of course, none of these navigational challenges are new, it is just that the use of a machine in conjunction with other systems points up these difficulties in an obvious way. In the recent past the mariner has happily used relative navigation and not been forced to acknowledge such mystifying details as datum shifts and skewed data. In addition, the mariner’s brain has tolerated inconsistencies which an ECS rejects.

As the ability to navigate ever more precisely becomes widespread it is also apparent that the accu- racy of the chart itself needs to be known and taken into account. When a charted detail, displayed on an ECS, can be seen to be inaccurate (i.e. the stated line of a charted track line or transit does not agree with the readout from the ECS’ electronic bearing line), is it the chart data which is at fault or is the fault due to the way in which the ECS presents the data or is it a com- bination of the two? How does the operator decide? It seems that, at least in these initial stages of determining the user’s requirement, the ECS poses more questions than it solves. It also serves to highlight the flexibility of the human brain (and the need to keep at least one on the bridge of a ship).

4 Conclusion

The case for proceeding with WECDIS will naturally take into account manpower and financial considera- tions. However, its main benefit, and the justification for its introduction into service, will be the ability it gives the bridge team, reducing in size but facing a ris- ing work load, to concentrate on safe navigation. It will do this without the distraction of the important but repetitive requirement to ‘fix’ the ship, something which is currently achieved using methods prone to time and human errors. There will be a requirement to check the system’s accuracy, although all sources of position can be displayed simultaneously to the opera- tor and discrepancies outside the expected tolerance of specific inputs will be apparent. However, when trusted, as it will be, the use of WECDIS will revolu- tionise warship navigation and will see the role of the NO continuing the recent trend towards that of naviga- tion management.

As it is introduced worldwide, ECDIS and its use can be expected to generate vigorous debate and, in the light of experience, change. However, there remains the challenge for the members of the IHO of providing an adequate quantity of S-57 data in a relatively short time frame. They are already on their mettle because the new technology allows measurements to be made with a precision not thought of when producing paper charts. For the RN the greatest challenge is to deter- mine how best to use this new technology, integrate it with current systems and ensure its training methods can cope with it while maintaining any necessary tradi- tional skills.

5 Acknowledgments

This work was carried out with the support of Captain Naval Operational Combat Systems, the Directorate of Operational Requirements (Sea), the Directorate of Naval Operations and the Ministry of Defence Pro- curement Executive (SESI 5).

IEE ProcRudar, Sonar Nuvig., Vol. 144, No. 3, June 1997 147