Advantages of Automatic Chart Corrections


Correcting charts manually is a monotonous affair and prone to errors. Automatic updates remove a major source of human error.

Labour and time saving

The number of charts required to be corrected depends on the size of portfolio carried by a ship. ISM requires all charts on board be kept updated. A ship could carry up to 5000 paper charts. Automatic updating of charts saves thousands of man hours otherwise spent on manual chart corrections. This job carried out by the navigating officer is repetitive, tedious and downright boring especially when there are hundreds of charts to be corrected every week.


Master gets the corrections when he wants like before entering a busy harbour or transiting through a tricky narrow channel. He doesn’t have to wait for the NtM packs to reach by post. 

Cost effectiveness

Chart service providers normally incorporate cost of corrections at the time of buying the ENCs. This is a yearly cost recovered at the time of renewal of licenses. The logistical cost ofupdates is minimum as they are disseminated through the net. As far as the end-user is concerned there is no separate charge for the updates. One year updates are paid for at the time of annual subscription. An important advantage of automatic updates is if you do not receive the previous update DVDs the chain of corrections is not broken. Whereas if you miss an in-between NtM booklet you will have to order it again. In the ship’s bridge you will find many drawers are filled with old NtM packs. Since it is very difficult to correct all charts on receipt of the NtMs, the mariners save old NtM packs to be used later like when there is a change of route and different charts are required. At that time the uncorrected charts are taken out from the drawers and corrected from the old NtM packs stored in the drawers.

Ships generally do not have a policy for preserving the old NtM packs. When she runs out of storage space old packs are disposed off. Sometimes Masters do not trust corrections of old charts carried out diligently and order for new ones even if they are not superseded.

Reduced carbon footprint

Transport those heavy NtM packs around the world adds to the carbon footprint.

Marine Incidents

An uncorrected chart is a threat to the safety of a vessel. If you knew that there would be an incident every time you sailed with bad charts then you would be more careful. It is because people get away with uncorrected charts very often that you are tempted to take chart updating lightly.

When you consider the cost of a vessel and its cargo, the accuracy of the chart becomes paramount. Even a single incident can cost millions.

How often does an incident occur? This is a difficult question to answer. If we go by the pyramid philosophy then for every reported incident there are 100 more which were never reported. For those who are interested to know about marine accidents look in the IMO's GISIS database. Or take a look at MAIB, BSU, ATSB, NTSB, TSB Canada, Marshall Islands and Isle of Man reports online. You might see if the Nautical Institute's MARS database has something and the Confidential Hazard Incident Reporting Programme.

There are quite a few incidents caused due to charts. Examples for not updated charts are Joshua Slocum and Globtik Sun, inaccurate/old charts (Pacific Challenger, Sanko Harvest, Rocknes, Octopus, Sea Diamond), use of inappropriate chart scale, wrong charts entirely. Sometimes it happens.

There is an interesting site ‘Centre for Tankship Excellence’ created by a naval architect, Jack Devanney. He is a career tankerman and has spent a lifetime in the tanker industry. He started this portal because he felt the oil tanker industry has lost its way. It is a very well researched web site for those in the tanker industry. Here there is a database of tanker casualties that is openly available to the public. If we check this compendium of large tanker casualties and spills we can get a fair idea of marine incidents caused due to navigation errors listed under NC. Shortening this list further to only those primarily caused due to bad charts meaning either ship did not update the charts or did not carry the appropriate charts, here is the list:

Date - Ship - Name - Dead - Volume - Comments

1975-08-15 globtik sun 61110000 hit platform off Galveston, bad charts, bad plotting

1984-10-01 aguila azteca grounded off Bermuda, chart inadequate, reef not shown, no spill

1991-02-14 sanko harvest N 750000 chart not uptodate, hit poorly surveyed shoal, sank

At 0130 on August 15, 1975, M/V Globtik Sun struck an unmanned Chevron Oil Company oil production platform approximately 100 miles from Galveston while en route from Aruba to Baytown, Texas. …..Apparently, the ship was on autopilot with the radar turned off when the watch was relieved at midnight. The charts that were in use were not up-to-date and showed no fixed structures on the ship's trackline. When the radar was turned at 0030, nothing was visible. At 0045, the radar revealed an object approximately 9 miles away on the starboard side of the vessel. The Captain of the vessel claimed that he saw no navigational lights on the platform even though a Chevron spokesman said they were functioning properly. The mate failed to plot the object. At 0130, the port bow of the vessel struck the eastern side of the platform, opening up a gash 2 feet wide by the length of the bow tank….. The Globtik Sun was later sold for scrap.

Sanko Harvest was approaching Esperance at the end of a voyage from Florida loaded with fertilizer. She had to pass thru the incompletely surveyed Recherche Archipelago. She struck on a shoal that was uncharted, but the Australians had issued a correction which noted this shallow area without giving the depth. This correction had not been entered on the Sanko Harvest's charts.

There are some other websites such as Marine Accident Incident Board (MAIB) which maintain similar databases.

In the MAIB there is no separate list of accidents caused due to charts. Here I found an interesting incident. The ship Pride of Canterbury ran over a wreck which the navigators on board probably misunderstood the symbol on the ECDIS. The ship had a fully approved ECDIS. But apart from the Master the other deck officers were not trained on this subject. In an ECDIS the symbol of a wreck can be totally changed based upon the user’s choice of settings. The traditional ….. symbol of a wreck can become a screw-head ……. If the user changes the safety depth settings. This is not an INT1/NP5011/INP5020 symbol but an S52 symbol.

Masters Dream Come True

Automatic updating is a boon to the Master and for this feature alone every Master should insist upon electronic charts. It removes the weakest link in the chain of chart correction. Corrections issued from the HO can be directly applied without bringing an error-prone human in the loop.

Next to accuracy is the speed of applying the corrections. In this age of reduced manning Master can utilize the second mate for other equally important tasks on the ship.

Chart corrections usually took hours on the chart table. It can be now completed within a few minutes with the click of a button and relieve the second mate for cargo work in the port or concentrate on safe navigation at sea.

Automatic updating has helped the Master to update his charts before entering the harbour or before transiting through difficult patches at sea such as narrow straits, heavy traffic sea lanes and congested anchorages where it is critical to have the latest information. Information about a sunken vessel, a buoy adrift or dysfunctional radio beacon needs to be immediately applied on the chart.

Keeping Your Charts Up to Date - Part II - Regulations

Regulations & Interpretations

Before July 2002 SOLAS Chapter V Regulation 20 stated that All ships shall carry adequate and up-to-date charts, sailing directions, list of lights, notices to mariners, tide tables and all other nautical publications necessary for the intended voyage.

There was no distinction between private and official charts. As long as there were paper charts SOLAS did not feel the need to protect mariners from ‘private’ charts. The cost of a paper chart is heavily subsidized so private companies cannot compete with government here.

Digital charts were started in the eighties by some private entrepreneurs. It was targeted towards the light marine industry. With the advent of electronic charts in the nineties SOLAS felt the need to amend the regulations in order to protect the mariners.

In 2002 a nautical chart was redefined as one issued under the authority of the government. Under the current SOLAS regulation all ships must carry nautical charts and publications necessary for the intended voyage which are adequate and up to date. Thus the official and private charts came into being.

Carriage of Goods By Sea

Most countries have adopted the Hague rules or the Hague-Visby rules to stipulate the carriage of goods by sea. Under Hague rules a vessel must be equipped with up-to-date charts and notices to mariners. Charter party agreements between the carrier of goods and the cargo owner contain the seaworthiness clause. It implies that if a commercial ship does not have up-to-date charts and notices then she is not seaworthy. This makes it liable to be ‘off-hired’. Considering that charter rates run into thousands of dollars per day, this could result into a big loss for the concerned party.

Note, under the Hague rules there is no differentiation between an official and a private chart. 

What is an up-to-date chart?

To a second mate appointed as the Navigating officer up-to-date means charts corrected to the notices that he has received on board. Even today many ships receive their updates by post. Sometimes the NtM packs are more than two months old before they reach the ship. Today some chart agencies use email or radio broadcast to promulgate the notices. This has improved the situation tremendously. 

To the HO up-to-date means up to the notices that has been promulgated via the NtM booklets or as Navarea warnings/ Navtex/ EGC messages.

How are digital charts corrected nowadays?

Let us see how C-Map does it. At C-Map headquarters they receive chart corrections from contracting hydrographic offices all over the world. They come weekly, fortnightly or at other regular periods. At the headquarters the updates go through quality control and are checked for consistency. Once they are tested and have passed the quality control the updates are made available to the user via a server.

Individual users access the C-map servers from the internet. Each user is checked for validity and their present status of chart database. The customer is then allowed to receive the charts corrections in the binary format. Typical size of chart correction for a world database of about 22000 charts is about 50Kb for one week of corrections. It can be easily downloaded onto the customer’s system. It is a well proven system and has been running now for many years without a hitch.

The service is available on all major satellite service providers such as Iridium, Geonet and Inmarsat. Those ships who do not want to use online system because of high cost or virus threats can avail the email attachments facility.

Online Updating of Digital Charts

Prior to downloading updates, it is possible to estimate the size of the data that will be received.

Updating via E-mail

For applying the updates using the E-mail service a request for updates has to be sent to the service provider.

The server automatically generates updates for your databases and sends a reply in about 5 minutes. If the size of updates exceeds your requested e-mail size, you will receive several e-mail messages, each of which does not exceed the requested e-mail size.

The next step is to apply the updates to the chart database. Facility is provided to review the updates in the list of updates.

The list on the right part of the panel displays a four level directory tree.

The first level of the directory tree is the list of hydrographic offices that have issued the received updates.

The second level is the list of chart numbers or corresponding datasets to which the updates have been applied.

The third level is the list of update files containing the updates (the third level entry consists of the update file number, update file issue date, and system ID of the update dataset).

The fourth level is the list of updated objects. The list entry consists of the name of the object and short description of the correction. It does not contain the past and present cartographic object position; for example, if coordinates of an object were changed, it is just marked as “Moved”.

Reviewing Chart Updates

There is a possibility to select a single dataset (electronic chart) and then review the changes in each subsequent incremental update.

The chart data (chart number, source hydrographic office, issue date, and last update date) can be displayed in the Picked chart window of the Chart Updates functional panel and the list of updates (the books (update files), in which the corrections were published, with corresponding issue dates) for the chart can be displayed in the Last 10 Updates window.

Figure - Highlighting the Updates on a chart.

Chart corrections add to the price of a chart. In order to reduce the prices there is a different system for the non-SOLAS class. For example the light marine class which falls outside the SOLAS regime can decide for itself how often they need to have the chart corrections.

The chart service providers sell charts updated to a particular date. New updates are brought out typically every 6 months in areas which see frequent changes. It is left to the end-user to decide when to replace their charts. Here the market forces decide the price and volume of sales.


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.