Nautical charts

 

Eric Geenen (for Syllogic)


The days are over in which ships were staying close to the land to navigate. Major progress has being made with regard to the the means to navigate the seas and oceans with an acceptable level of safety. However, great pains are still being taken to preserve save passages.

Beside ECDIS there is an array of other nautical navigation software with various kinds and qualities of charts, options and features. Fully integrated intelligent navigation systems, however, are not yet on the market. Robosail is a project that should change this. The aim of Robosail is to develop an intelligent ship navigation system for sailing yachts that is capable of combining various sources of information. The system should give information for example about the actual current, weather, positioning, fuel, but should also give advise of the best course and the optimal sails-management.

The electronic nautical charts as a basis

At the basis of such a system lays a spatial database that refers to coordinates in the real world.

The nautical chart can be described as the topographical map of the water, however specifically designed to navigate. It is showing the depths of the water, obstructions, and dangers, as well as showing vital information to navigate. Like compass roses, compass deviations and sometimes a hydrograph.

The representation of the curved surface of the world is usually given in the projection of Mercator, because this projection possesses the best characteristics to navigation. The disadvantage of the Mercator projection is that the vertical scale is dependent on the latitude, and hence some distortion is to be seen.

Liability

The nautical chart is, contrary to the topographical map, continuously updated. For the paper nautical chart this means that the chart publishers and sellers, as well as the users, after buying the chart, are expected to keep the chart up to date with the latest information. This information is given to them in the form of the notices to mariners (NtM).

One of the biggest differences to realize between the nautical chart and the topographical map is that dangers mentioned on the topographical maps are visible to the naked eye in the real world. Whereas many dangers under the water are not to be seen on the surface, but are only to be seen on the chart. Therefore a mariner must have a great trust in what is displayed on his nautical chart.

Raster, vector and hybrid charts

Technology gives us the possibilities to draw charts on computers in a raster, vector or intermediate form. The aid to navigation can give the user great benefits, if the electronic nautical chart is used correctly.

In the past the cartographer was responsible for the information given and omitted in the nautical chart. Sometimes he or she omitted elements so that the information given in the chart would be beneficial to the safety of and ease of use to the mariner.

Nowadays there are systems that make it possible to omit, or better: to switch off, layers with vital information. The information not visible in the chart may lead to dangerous situations, unless the navigational system understands the situation and reacts accordingly. A ship’s navigation system for example could set of an alarm to warn against collision or grounding, although the display of the layer with information about other ships is turned off.

Standards

Insofar there can be spoken of international standards, these standards are developed by the International Hydrographic Office. One of the important standards described by the IHO is the standard describing the IHO Transfer Standard for Digital Hydrographic Data (S-57). Beside that, there are various other important specifications made by the IHO (for example S-52) and the IMO (Performance Standards for ECDIS).

The electronic nautical charts proposed by the IHO are in a structured standard format DX-90, which may not be changed for commercial purposes. Changes to this standard format by manufacturers are done in the way of designing new formats for the SENC.

The integrated system of Robosail

Robosail uses more than an electronic chart to navigate the seas with the highest efficiency and best performance. For a good judgement of the critical decisions to be made during voyages, the navigation system should give the appropriate information to the user, but should understand this information itself as well, to give advice and support. Robosail should be able to give advice concerning: wind and weather, which is updated via a modem link; sea currents; sails management; accurate positioning, including historical track and course prediction; dangerous situations ahead; other sea traffic and if desired tactical information under racing conditions.

Link: Robosail