Putting the mariner in the picture
The Navigator looks at innovations in the field of visual aids to navigation, including LED lights and ‘smart buoys’ that can broadcast their own position. How do they benefit the mariner – and what’s coming next?
The development of visual aids to navigation has been a process of ongoing innovation, from a piece of wood moored to a block of stone some 2,500 years ago, to today’s high-tech intelligent lantern or floodlight, capable of switching itself on when needed.
Aid to navigation engineers have continuously worked to ensure high reliability, simplicity, maintainability and long service life at minimal cost.
Seeing the (LED) light
The introduction of LED (Light Emitting Diodes) as an aid to navigation light source has been one of the greatest achievements in recent navigation history. This is due to their long service life, low power consumption, robustness and reliability in rough environments, as well as their high level of visual conspicuity – in other words, they are very easily seen and identified.
From the mariner’s point of view, LED lights often seem more conspicuous, compared with traditional incandescent lights. This is due to their narrow spectral distribution. LEDs emit near-monochromatic light while incandescent light sources are more broad-banded. The colour emitted from an LED appears more pure, making it less likely that the mariner will mistake one light for another. When they flash, LEDs produce a rectangular flash intensity profile. They do not have the glow-up and glow-down period of incandescent lights, which further enhances their performance.
Today, LED lanterns are used in almost all buoys. LED lanterns and LED sector lanterns are also available for short- and medium-range beacons. High-power white LED lanterns with a range of up to 20 NM are also available, and some aid to navigation authorities have replaced old revolving optics with this type of lantern. This, however, means that the sweeping characteristic (the sweeping loom of the light) of traditional revolving optics is lost.
Other authorities have chosen to retrofit tungsten filament lamps with very high intensity LED light sources within the original revolving optics, thus retaining the high luminous intensity from the large lens and the sweeping loom of the light.
New technology in practice
The new yellow/blue emergency wreck marking buoy is another example of taking advantage of LED technology. At night, this type of buoy alternates between a blue and yellow light, making it very different from other marine signal lights.
Satellite-based positioning and precision-timing services have enabled automatic position monitoring of buoy positions, as well as synchronisation and sequencing of lights. Synchronising and sequencing the flashes of a group of aids is now commonly used in many fairways and channels. This increases the conspicuity of the aids, particularly in high background light conditions.
An example of the effective use of synchronised lights can be found in the Danish Great Belt. When passing Hatter Barn/Hatter Reef, outgoing vessels must take a hard starboard turn. In this area there used to be two to four groundings of vessels missing the turn every year. Since the Danish Maritime Authority (DMA) introduced a “wall” of synchronised LED lights marking the reef, the groundings have ceased entirely.
Sequencing light is another way of strengthening the conspicuity of a group of lights. Sequenced lights are seen as a ‘runway’ marking safe passage through a channel. Synchronising and sequencing of lights is particularly valuable in high background light conditions with a lot of rivaling lights. Visit The Navigator blog at www.nautinst.org/ navinspire to see a You Tube video showing the advantages of sequencing lights.
Broadcasting the benefits
The reduced power requirement of LED lanterns provides surplus electrical power for other services, such as meteorological and hydrographic sensors. There are a number of sensor-equipped buoys in the Great Belt area. Information is broadcast by radio to the shore every ten minutes and published on the internet. In future, information services like this are expected be part of the e-navigation services. The introduction of AIS (Automatic Identification System), and in particular AIS aids to navigation, now makes it possible to broadcast the operational status of any aid to navigation, either directly from the aid, or indirectly using a shore-based base station (synthetic AIS aid to navigation). The information can be viewed on AIS-enabled ECDIS, Radar or other navigation displays, appearing at the location of the charted aid to navigation object.
Another option is the so-called virtual aid to navigation. This comprises a signal broadcast to a location in a waterway where there is no physical aid present. Virtual aids to navigation are very useful when an unexpected situation occurs and requires immediate marking, e.g. a wreck.
At the moment, authorities are looking into whether and to what degree these “electronic” aids can replace their real physical counterparts. It is the opinion of the authors of this article that electronic “synthetic” or “virtual” aids to navigation will never fully replace existing visual aids; their role will merely be to augment and supplement them. The primary purpose of visual aids is to provide unambiguous confirmation of what the navigator can see, no matter how many electronic gadgets are available.
That is why operational reliability has been at the core of the development of aids to navigation since the beginning of time, and why it will continue to be the primary design criteria for the foreseeable future.
Authors: Jorgen Royal Petersen, Senior Aids to Navigation Engineer and Omar Frits Eriksson, Director, Maritime Technology, Danish Maritime Authority