Aids to Navigation (AtoN)

Guidelines and recommendations for Aids to Navigation (AtoN) are agreed internationally and published by IALA (2010). This section discusses AtoN positioning systems and facilities in the context of the planning and design of approach channels, but does not take precedence over specific IALA recommendations. Navigation itself may be understood as monitoring one's position geographically within a constrained waterway.

There are several navigation methods widely used in the maritime world:

 Visual navigation that uses optical observations

 Radar navigation that uses radar observations

 Electronic navigation that uses positioning signals from satellites and other systems

 Celestial navigation

Today, all are generally used in combination as appropriate. Also, VTS/VTMS (Vessel Traffic Service) systems are monitoring and assisting safe navigation from shore via radio in many port and coastal areas.

Aids to Navigation are needed where there is a lack of adequate natural visual leads.

They are of four basic types:

 Directional guidance, i.e. lateral positioning reference in a channel

 Longitudinal positioning reference to a channel

 Acting as a fixed point while navigating, i.e. position reference

 Warning of possible hazardous areas and objects

Further information on AtoN can be obtained in IALA (2010), USACE (U.S. Army Corps of Engineers 2006), and ROM (2003).

4.6.1 Channel Markings

Channel markings are prescribed for both visual and radar navigation. Channel markings may be located either along the sideline of the channel e.g. buoys or channel centre line, e.g. leading lights. The properties of markings may be summarised as:

 Leading lines along centre lines act as a very powerful tool for lateral positioning, but poor for longitudinal positioning

 Leading lines crossing the channel are accurate tools for longitudinal positioning

 Single markers are mainly for longitudinal positioning, but may be effective for lateral positioning when used in long, wide channels

 Paired markers act for both longitudinal and lateral positioning. Alternatively, centre line markers may be used

 Single marker on a curve turning point may act as position reference around the turn

 Single marker may be used for warning purposes. For example, warning about a hazardous wreck or a rock

By combining types of markings, one may design a channel that is safe to navigate. The required AtoN are related to channel properties, including width and curvature, weather and traffic conditions.

There is a very strong connection between channel dimensions, alignment and markings.

A curvy channel needs good lateral and longitudinal positioning and all the curves should have turning point reference or some other provision.

Theoretically, the more channel markings provided, the easier it is to navigate. However, there is a saturation point where adding AtoN does not help positioning further. One has to appreciate that too many markers may be confusing. Also lateral marks themselves effectively narrow the channel. The task is to find the optimal solution between channel marking and channel dimensions. Usually, this point has to be found by simulations in the detailed design phase. Because ships use a variety of AtoN in addition to channel markings the designer should pay attention to possible channel crossings to avoid creating confusing navigational situations with too many marks.

A minimum requirement of channel marking is that at least one marker should always be visible (by eye or radar) on either side of the channel [USACE, 2010]. With this rule and knowledge of visibility conditions in area of interest, one can calculate maximum

distances between markers. Maximum marker spacing is then less than minimum visibility required. The ship size, speed, bridge visibility and the use of electronic navigational aids may dictate that the minimum distance required is smaller than the minimum meteorological distance considered.

One possible way to mark a channel is to place a marker in all vertices of sidelines (‘corners’). If straight parts are longer than the maximum spacing allowed, there is always an option to place additional markers along the straight sideline. This marking technique is common in curved channels. An alternative to both straight and curved channels is the use of centre line buoys, particularly in two way channels. Fewer buoys are needed and the factor of paired buoys creating additional channel obstructions and small craft restrictions is avoided.

In simulation studies, it has been shown that gated markers are superior in straight parts of channel compared to single markers on sideline vertices [USACE, 2010]. As mentioned earlier, paired makers are effective for both lateral and longitudinal positioning.

In summary, every channel is an individual case and should be studied as such. There is no universal optimal solution, but a variety of marking solutions and techniques. The proposed marking systems should always be studied in simulation, at least on their critical points. Designers should always consult an AtoN expert while planning the AtoN equipment of a channel.

4.6.2 On-Board Navigation Systems

The basic goals of an on-board navigation system are to recognise and monitor both the vessel's absolute geographical position within the area and the vessel's relative position to known fixed and moving objects, both natural and man-made.

4.6.2.1 Visual Navigation

The primary means of visual navigation is manually plotting on a paper chart using two or more compass bearings of geographical features. The use of horizontal and vertical sextant angles, etc. can be considered impractical and obsolete. Relative position fixing can be facilitated through the observation of various forms of leading marks, including geographical features and channel buoys. Night vision equipment and binoculars are probably the only optical aids that may be found in use today.

4.6.2.2 Electronic Aids

Electronic aids include radar, ECS, ECDIS, GNSS, DGPS, eLORAN, e-Navigation, AIS, PPU and miscellaneous systems. Each of these systems and instruments is described below. The designer shall always keep in mind that systems mentioned here are not available all the time and for all vessels. Therefore, if necessary, it should be possible to navigate without this equipment.

Radar can be used for both geographical position-fixing and for relative position monitoring through a variety of techniques. Radar technology continues to develop. For channel marking, the addition of radar beacons or Racons can significantly improve the visibility of important buoys, etc.

ECS is a non-IMO approved navigation information system that electronically displays vessel position and relevant nautical chart data and information from an ECS Database on a display screen.

ECDIS (Electronic Chart Display and Information System) equipment is specified in the IMO ECDIS Performance Standards and with adequate back up arrangements can be accepted as complying with the up-to-date chart required by regulation V/19 & V/27 of the 1974 SOLAS Convention.

GNSS (Global Navigation Satellite System) is the standard generic term for satellite navigation systems.

DGPS (Differential GPS) is an enhancement to GPS; the result is a significantly more accurate and reliable position fix.

eLORAN (Enhanced LOng-RAnge Navigation system) is an independent, dissimilar complement to GNSS. The international maritime community now understands that its future digital e-Navigation environment needs an internationally agreed alternative system to GNSS. eLORAN is the only viable candidate.

e-Navigation (electronic Navigation) whilst not strictly a position-fixing system, is a navigational concept which will have far reaching influences on the future of shipboard navigation systems and techniques. It is an IMO-led concept based on the harmonisation of marine navigation systems and supporting shore services driven by user needs.

AIS (Automatic Identification System) is a system used by ships and Vessel Traffic Services (VTS, see section 4.6.3) principally for identification and locating vessels. Work is now ongoing to facilitate the transmission of data such as identification, meteorological and tides from navigation marks via AIS.

PPU (Portable Pilot Unit) is a notebook computer-based system which, depending on its level of sophistication and manufacturer, is able to provide the Pilot with his own wholly or partially independent navigation and manoeuvring monitoring console.

Miscellaneous systems are more fundamental equipment that are also in use and include but not limited to Gyro, Magnetic, Fluxgate and GPS-based compasses, Echo sounders and sonar devices, etc. Additionally, there are numerous docking aid systems.

There is also a wide range of newly developed AtoN (section 4.6.4).

4.6.3 VTS/VTMS Systems and Impact

Vessel Traffic Services (VTS), often referred to as VTMS (Vessel Traffic Management System), are shore-based port or coastal region traffic management systems. The types of service range from the provision of information to ships, to extensive management of traffic within a port or waterway.

The following text is the IMO definition of VTS (IMO Resolution A857 (20)):

 Vessel Traffic Service (VTS) – a service implemented by a competent authority, designed to improve the safety and efficiency of vessel traffic and to protect the environment. The service should have the capability to interact with traffic and respond to traffic situations developing in the VTS area.

VTS should comprise at least an information service and may also include others, such as a navigational assistance service or a traffic organisation service, or both, defined as follows:

 An information service is a service to ensure that essential information becomes available in time for on-board navigational decision making

 A navigational assistance service is a service to assist on-board navigational decision making and to monitor its effects

 A traffic organisation service is a service to prevent the development of dangerous maritime traffic situations and to provide for the safe and efficient movement of vessel traffic within the VTS area

Potential for confusion arises as it is incumbent upon the navigator to be familiar with the types of service being provided by the VTS in a particular area. The nature of a specific VTS should be widely and clearly promulgated. (Usually this can be found in the Admiralty List of Radio Signals (ALRS) and on charts, etc.).

Traffic management implications from a channel design and operation perspective are primarily it about what type of service is available to assist the navigator. For example, a narrow channel in a busy port approach may require a Traffic Organisation Service, whereas a relatively quiet port may only need an Information service.

A VTS is particularly appropriate in an area that may include any of the following:

 High traffic density

 Narrow channels, port configuration, bridges and similar areas where the progress of vessels may be restricted

 Existing or foreseeable changes in the traffic pattern resulting from port or offshore terminal developments or offshore exploration and exploitation in the area

 Traffic carrying hazardous cargoes

 Conflicting and complex navigation patterns

 Difficult hydrographical, hydrological and meteorological elements

 Shifting shoals and other local hazards

 Environmental considerations

 Interference by vessel traffic with other marine-based activities

 A record of maritime casualties

 Existing or planned vessel traffic services in adjacent waters and the need for co-operation between neighbouring states, if appropriate

4.6.4 Future Development of AtoN

There are several very interesting development projects and new designs in the field of AtoN. The lighting of AtoN is evolving with LED (Light Emitting Diode) systems. The lighting power of an individual buoy may be 10 times greater than with other lamp systems. Additionally, only 25 % of the original power may be used. Another development is the synchronisation of channel buoy lights.

Another development is remote monitoring of AtoN. GNSS and radio modules are placed in an AtoN so that it knows where it is and where it should be. The AtoN notifies the appropriate authority when it is misplaced or it has some other malfunction, e.g. battery failure. Polling of the AtoN for its position and status is also possible. This remote monitoring system can have huge potential savings in channel maintenance.

Combining AIS with AtoN are new concepts that are under development. In one scenario, an AtoN will have an AIS transmitter in it so it may be seen as an AIS target on an ECDIS screen. Remote monitoring is possible by this method too. A potential problem of this system is the already crowded AIS radio frequency. Another concept with AIS and AtoN is that there is no real physical AtoN present, but a virtual AtoN is displayed on the ECDIS-screen via AIS. This is accomplished by broadcasting the virtual AtoN from an onshore station to all ECDIS users. This is a handy and fast way to mark a danger, as for example in the case of a wreck, there is no need of expensive AtoN installations. This application of AtoN is recommended only as a temporary marker, as it should be noted that vessels that do not use ECDIS cannot see a virtual AtoN.