The increased use of electronic charts has to some extent changed conditions in shipping. When used correctly, electronic equipment has the potential to make shipping safer, but not without introducing certain risks. There are different types of electronic charts, raster charts and vector charts. Navigating with electronic charts (i.e. with ECDIS) requires reserve systems (another ECDIS or paper charts).
The chart portfolio in the ECDIS system consists of a number of cells. It may be said that each cell represents one nautical chart. The name of the cell consists of a code of eight characters. The first two designate the nationality of the country producing the cell. The third designates the navigational purpose (scale area), and the last five designate the geographical area that is covered by the cell. A geogra-
phical area may be covered by several cells which are made for use in different scales. It is important to have onboard access to cells with all the different scale areas that may be required.
One error that seems to be common is that the system operator (mate or officer) tends not to use cells in the scale areas which are needed. The
operator probably believes that he is using the correct cell, but in fact is using another. The situation may then arise when you zoom into a small-scale chart (i.e. with a large area) and obtain an image on the screen which appears to be on a large scale (i.e. of a small area). In fact what is being displayed is an enlarged image of a chart in the wrong scale, which does not have the level of detail required. Even if the system is set for “best scale”, it is necessary to check that this is working. At the very least, you must ensure that the best scale is available for the system.
Blind faith in electronics
Always be cautious when using electronic navigation aids. There may be in-built, significant errors in both electronic charts as well as paper charts, both in terms of position and depth. In Swedish waters there are areas which have not been surveyed since the nineteenth century. A position on charts covering such an area may have an error of between 40 and 50 metres. Giving this due consideration, it is unreasonable to state position coordinates from a GPS system to several decimal places. More important shipping lane areas are measured using modern methods and the errors are considerably less in these areas. One of the oldest rules of thumb for safe shipping is still valid: never trust only one method of navigation; always confirm it using other methods.
Information about all cells on the market is available from the two companies which supply them:
www.primar.org and www.ic-enc.org. Information may also be found at the Swedish Maritime Administration, www.sjofartsverket.se and in Ufs A 2010.
The passenger ship was on a round trip and navigating with the aid of an electronic chart display. The operator had zoomed into the area in question but did not realise that the details of the display did not increase when zooming. The ship grounded.
Iu jour. no. 1999-35348
A tanker ship was passing an area with relatively new traffic separation. It was not known on the ship that the supplier of the electronic charts (ECDIS) had withdrawn one chart and replaced it with another. The ship was sailing on the old chart and was incorrectly separated. The supplier does not automatically replace old charts even if a company subscribes for updates; new charts must be actively ordered. The ECDIS does not clearly indicate when a chart is too old. Since the chart portfolio was not updated and because it affects safety at sea, the case has been passed on to the prosecutor.
Sfu jour. no. TSS 2010-2408
A chemical tanker was sailing on the open sea and passed over a bank in shallow water. At the shallowest point there was only one metre or so of water underneath the ship’s hull. That margin disappears quickly if a ship squats or if there is a swell. The situation was detected by the VTS and a ship inspector came onboard in the next harbour. The depth data and depth contours on the electronic chart were not displayed as intended, for some unknown reason.
Sfu jour. no. TSS 2009-4055