CYCC News 17 June 2004

Visual Aids to Navigation

a CYCC Position Paper prepared by David Darbyshire (Hon Sec)

Cruising yachtsmen have a particular interest in visual aids-to-navigation, since they tend to navigate by these aids when in sight of land, in shipping lanes or when approaching a fairway or harbour. Following on from CYCC's letter to Trinity House of 29 January 2004 about the GLAs' "Vision 2020" strategy, CYCC members will wish to be aware of current thinking of the UK & Irish Lighthouse Authorities (GLAs), the Nautical Institute (NI) and the Royal Institute of Navigation (RIN) about the needs of leisure as well as commercial navigators.

About a year before "Vision 2020", The NI published research into navigational practices and sought to assess the future need for visual aids. The GLAs and the RIN agree with the NI's findings: the GLAs from the perspective of their duty to provide "such aids to navigation as the volume of traffic justifies and the degree of risk requires" and the RIN from the viewpoint of its special interest in satellite based navigation systems.

The NI's conclusions reinforce the need for navigators' spatial and situational awareness of surrounding hazards and traffic. The NI endorses the requirements under STCW 95 for navigators of merchant ships to fix their positions by more than one method whenever circumstances allow and to positively identify all relevant navigation marks. The research notes a shift in focus towards navigation in coastal waters and the approaches to harbours now that landfalls on arrival from the high seas are made reasonably certain thanks to satellite navigation.

The central role now played by satellite, radar, radio and related systems in supporting ship-borne navigators and authorities on-shore is well recognised. However, the NI affirms that traditional techniques continue to stand the test of time. Direct visual reference is essential for safe pilotage, whether it is to buoys and beacons, which indicate leeway, set and tidal flow, to transits and leading lines or to clearing bearings from lighthouses, natural features and floating aids.

The NI concludes that "there will be a continuing need for fixed and floating visual aids to navigation, not so much for the purpose of position fixing but increasingly so for visual reference and to alert the mariner to the fact that he may be standing into danger."

The GLAs, the NI and the RIN and point out:

• Global Navigational Satellite Systems (GNSS) combine with shore-based electronic aids and with ship-borne radar and electronic charting systems to revolutionise the way in which mariners establish a vessel's position. Technical advances will continue to improve accuracy (differential Global Positioning Systems), to provide back up (developments of the Russian GLONASS and the European Galileo system, due to be operational in 2008), to offer alternative methods of fixing (lobbying to extend Loran-C) and identification (Automatic Identification Systems - AIS). Progressively more pervasive monitoring and control of vessel movements by Coast Guard authorities and ports' Vessel Traffic Services is coming into force.
  
  
• Lighthouse authorities around the world are accordingly asking themselves whether and over what period traditional aids-to-navigation will be made redundant by evolving satellite, shore-based and ship-borne systems. They recognise, however, that visual aids still comprise the greatest number of aids to navigation and generally conclude that they will continue for many years to come. The GLAs specifically assert that: "both in the commercial and leisure sector, lighthouses, buoys and beacons will continue to play a vital role in a balanced aids-to-navigation system."
  
  
• All satellite systems are vulnerable - and this vulnerability is carried onwards to charting, radio and radar instruments that require GPS input. The RIN said, as part of an argument to extend Loran-C and reflecting other studies, notably those of the Volpe Centre of the US Department of Transport: "It is imperative that GNSS is never used in a safety-critical situation without some form of terrestrial back-up being available. Signals from GNSS are extremely weak when received on the earth's surface due to the very low power of transmissions and the considerable range of the medium earth orbits used by these satellites. No matter how diverse the signal formats or frequencies, all are extremely vulnerable to even very weak interference, which might be natural or man-made - intentionally or not so."
  
  
• The quality of satellite signals and of transmission equipment will go on improving, but failure is not unknown - individual GPS satellites do fail and typically take up to 48 hours to repair. The more likely cause of failure is that ship-borne equipment will develop a fault, be distorted by other on-ship transmissions or electrical fields or go down due to loss of power supplies. Power loss affecting position fixing, autopilots, radars and chart plotters is probably the highest risk for leisure craft, particularly sailing yachts.
  
  
• A position fixed by satellite is only useful if the charts on which the position is plotted are equally accurate and if the GPS position referred to WGS84 is restated when the chart is not based on the same system. The Hydrographic Office (UKHO) warns: "when closing the coast or in the vicinity of dangers, which may have been fixed relative to the coastline, vessels should always verify their GPS position in relation to the charted detail by using alternative methods of position fixing ... in all cases, prudent positional clearance should be given to any charted feature, which might present a danger to their vessel." This is because: "charts are compiled from the best source data available, but these sources are of varying age and scale ... the data may have been gathered when survey methods were less sophisticated than they are now."
  
  
• Electronic systems import their own risks of human error. Mariners tend to become over-reliant on these systems and are inclined to forget to make visual checks of the external environment and to refer to visual aids. A recurring message from the Marine Accident Investigation Branch (MAIB) is: "Some systems give a sense of security that isn't always justified. Navigation aids fall into this category, and there are numerous examples of watchkeepers who assume GPS is infallible and don't bother to cross-check the ship's position by independent means. Going aground is not popular."
  
  
• Both the NI's research and the GLAs' observations note that GPS is encouraging every kind of mariner to navigate not only closer inshore but to do so in conditions of darkness and reduced visibility where they would not have previously ventured.
  
  
• Fixing a ship's position by more than one method does not oblige navigators to use visual aids. GPS positions are typically combined with radar ranges and bearings to give a fix, thus saving the time taken to take and plot visual fixes. However, both for commercial navigators and for yachtsmen, who may not be able to use radar in any event, visual aids provide an alternative method very well adapted to building situational awareness. An MAIB report concerning a yacht noted: "Although the GPS was functioning correctly, no fixes were being plotted and no planned track for the approach had been prepared."

The NI consulted widely and internationally when making its research. The work confirmed that retention of visual aids for the foreseeable future is well grounded in the practicalities of safe navigational watchkeeping. It pointed out that the human and environment cost of even one serious stranding makes the sums involved in retaining visual aids seem relatively modest, if they assist the navigator to remain alert and avoid the hazard. Visual aids are therefore likely to be retained in most parts of the world and will be developed to meet new needs and make them more effective. Thus, the GLAs have already increased the number of buoys around the UK coastline and lit 50 hitherto unlit buoys. Racons are likely to be retained, AIS transmitters will be fitted to fixed and floating visual aids and most lit buoys will be re-fitted with LED lights. Research continues into the use of lasers to improve the visibility and sector distinction of fairway lighting.

Important sources

The Use of Visual Aids to Navigation, by Commodore David Squire CBE, JP, FNI, FCMI, Nautical Institute, October 2002, <www.nautinst.org>.

Vulnerability of Global Navigational Satellite Systems, especially a paper by Dr. Mark Ward and Captain Duncan Glass, Royal Institute of Navigation, April 2004,<www.rin.org.uk>

"2020 The Vision", Marine Aids to Navigation Strategy, General Lighthouse Authorities - Trinity House, Northern Lights & Irish Lights, draft December 2003,<www.trinityhouse.co.uk>.

Annual Notices to Mariners, No 19, United Kingdom Hydrographic Office, January 2004, <www.ukho.gov.uk>

Vulnerability Assessment of the Transportation Infrastructure Relying on the Global Positioning System, Volpe Centre of US DoT, August 2001, <www.volpe.dot.gov>.

Safety Digest - Lessons from Marine Accident Reports, the 28ft yacht Kishmul of Ayr accident, 1/2001, and Merchant Vessel Overview and Captain Spyros accident, 3/2001, Marine Accident Investigation Branch, <www.maib.gov.uk>.

Bridge Procedures Guide, International Chamber of Shipping, 3rd Edition 1998, <www.marisec.org>.