Because features that are shown on charts change either due to human intervention or natural change, it is vital to keep charts updated and corrected.

The changes that need to be made will be covered by the Notices to Mariners that the Hydrographic office issues each week.

Yachting magazines publish the more important changes that are relevant to small boats and craft which makes it easier for yachties to keep up with the changes that are specific to them.

Another source of corrections are the harbour authorities who publish detail of the changes for which they are responsible.


How to correct a navigational chart

Look up the number of the chart in the index of the Notices to Mariners. When you find the number you will see a list of all the corrections that need to be made to that specific chart. A number is assigned to each correction for identification purposes.

You will now need to look up the correction to find out the details. Large corrections are done by sticking a new section of chart to the original chart – make sure you line the insert up properly.

If a feature needs to be deleted, just draw two neat lines though the feature and any writing associated with it.

If a new feature needs adding, draw the symbol as clearly and neatly as you can. To keep the correction neat, use a special correcting pen. These are available in a pack including a stencil. If you are unable to get a chart correcting pen, use a fine nibbed, waterproof pen.

After the correction is made, you need to write the number of the correction in the bottom left corner of the navigational chart.

Anyone looking at the chart will now be able to tell if the chart is up to date.

The last line of a chart correction shows the number of the previous correction done – if this is not the last number at the bottom left of the chart then a correction has been missed.

A chart that has not been corrected is very dangerous as there are possibly new hazards or navigational aids that have been changed. Without noting these changes, navigation can be very difficult.


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