Keeping Your Charts Up-to-Date Part I - How Often We Update Charts

The End of an Era

For 30 years Mrs. Desai has corrected charts at Naval Chart Depot, Mumbai. She is a senior draughtsman there.

Her tools consist of a parallel ruler, divider, a plastic protractor for drawing circles and a plastic scale. She keeps a hack-saw blade to draw zigzag lines on the chart for submarine cables.

Lately corrections have started to come with accompanied tracings. The task has since become a little simpler. Nevertheless it is a tedious job and a very monotonous one.

There was a time early in her career when she used croquils with black and magenta inks. Now she uses Reynolds 040 ball point pens of appropriate colours.

“There are no unwanted ink-blobs with the ball point pen”, she says. 

On average she corrects 30 charts per day before they are sent to the ships and other end-users.

In the next few years it is inevitable that electronic charts will replace the paper charts. Mrs. Desai is grateful that by then she would have retired on a government pension.

To those who want to know how to correct charts she refers the Admiralty publication NP 294 How to Correct Your Charts the Admiralty Way.

Notices to Mariners (NtMs) have evolved from the time ships started sailing with paper charts. In those days a mariner depended on important navigational information passed by word of mouth amongst fellow mariners. At some point of time, about a hundred years back some Hydrographic Offices (HOs) started collating this information. They verified the information before distributing them to the ships through print. This lent it an authenticity.

Since then NtMs have become an integral part of charts and publications required to be maintained on board for safety of navigation.   

Many updates continue to remain in force till such time a new survey is carried out and a new chart is published. At that time all the reported information are verified and included in the new chart.

Now with the electronic charts on the verge of replacing paper charts, the need for manual updates and dedicated chart correctors will disappear for ever. At last this tedious job will be taken over by the machines.

The method of updating charts devised by those pioneer explorers since the 18th century can finally rest in peace.  

How Often Charts are updated

Consider the earth as a ball rotating around the sun. Seen from the space the form of earth has hardly changed over billions of years. As you come closer to the earth you find some natural activities which changes the topography of the earth. Activities like underwater volcanoes, tsunamis, earthquakes and such other violent natural phenomena which redraw the seabed, coastlines and islets.

Then there are regular events like monsoons and river flows which continuously change the topography of a particular region.

For example the chart in the northern part of Gulf of Khambhat (India) invariably gets outdated before long. A combination of river outflow and tides of above 10 meters cause strong currents and continuously change the seabed. Similarly pilots up the Amazon River find it useful to refer to Google earth as the paper charts continue to show islands which got submerged in the last flooding of the river.

Apart from the natural changes there is the human activity such as port constructions, marine incidents and such other things which have to be reported as chart updates.

These are the changes that actually take place. There are many places where the charts have been constructed from old surveys. They have to be replaced because the surveys were carried out using primitive instruments like lead line soundings and sextant angles. Where the ground control was established using astronomical observations. With navigators using accurate GPS there is a mismatch between the chart and the obtained satellite positions.  

Satellite navigation only arrived in the last thirty years. It will take many decades before the complete seas/oceans are surveyed to a satisfactory level of accuracy.

Ships are continuously plying on the seas, traversing in and out of busy harbours and waterways. Timely chart updates are critical for their safety. Even a small incident can result in a costly affair.

The number of chart updates being issued is going up every day. Today it is impossible to maintain all the charts using manual updating.

The number of changes varies on the scale and the area. There are more than 22000 electronic charts with C-map. Approximately 1200 charts need to be replaced every year. Or 24 charts per week. Apart from the replacements every week new charts are being added to the database. The number of corrections is only adding up every day. Only automatic updating can keep up with the issuing of regular chart updates.

Print-on-Demand Charts

Some advanced HOs have started the print-on-demand charts. With this facility whenever the customer asks for a chart he gets the latest chart corrected till date using the electronic form. This is another improvement from charts supplied earlier. In case the vessel is fitted with the printer then all the ship has to do is print out the latest chart whenever she wants.