Over reliance on electronic charts

We asked Simon Wilson, Equinox Sailing’s Chief Instructor if there are any pit falls in using electronic charts for passage planning.

For many sailors sailing in familiar waters, they are aware of any navigation risks and possible major dangers they face while sailing in those areas.  For sailors who sail in the same waters on a frequent basis, they may choose not to look at a chart for shorter passages within the known sea area and choose to rely on a chart plotter.

However when sailing in less familiar waters does a reliance on the chart plotter in familiar waters make sailors complacent?

There are two main types of electronic charts, ‘Raster’ and ‘Vector’.

‘Raster charts’ are an electronic version of a paper chart, what you see is what you get.

‘Vector charts’ use layering to add and remove detail depending on the level of zoom. Most chart plotters use Vector charts because of their ability to show more information than a Raster chart.

We do however need to be aware that a Vector chart, if zoomed out, may not show detail such as a drying area or a rock, which would be considered dangerous.  It is therefore important if planning a passage on an electronic chart, that the whole route is checked and zoomed in enough to ensure that you spot any dangers.

The image below shows the ‘The Island’ very clearly as well as depth on the Raster chart, but not on the Vector Chart as it has not been zoomed in enough.

Raster chart


Vector chart


Paper and Raster charts do have a slight advantage in the planning stages as the dangers are visible on the chart making it easier not to miss important details or dangers.

I have been guilty of not zooming in enough myself.  After the 2015 RORC St Malo race I decided to sail to Jersey as we couldn’t get in to St Malo.  I hadn’t slept much and due to the North Westerly wind I told the crew to sail close hauled and make our course as close to North as possible, popped a waypoint on the entrance of Jersey and that was that. As I hadn’t visited Jersey for a few years, I had a look at the almanac and I was reminded about Plateau des Minquiers a group of small islands and rocks South of Jersey.

Did I know about the Minquiers, yes I have sailed the waters around the Channel Islands many times, but I did forget. As I checked the chart plotter at a zoom level that didn’t show them, in my tired frame of mind I felt the course I had plotted was safe.

Thankfully I didn’t rely entirely on the chart plotter otherwise a very pleasant weekend might have been ruined, but once my mistake had been spotted, we tacked to ensure that we cleared them.

Electronic charts are useful, they make it much easier to plan a passage anywhere. With electronic charts it is possible to plan a route at home or on the train on the way to the boat, save the route and load it into the chart plotter upon arrival. But you do have to be careful as it’s easy to make a silly mistakes, and as we have seen in recent years with Team Vestas grounding in 2015/16 Volvo Ocean Race http://www.volvooceanrace.com/en/news/8549_Vestas-Wind-grounding-report.html   these mistakes can be costly.

A very useful feature of the RYA Chart plotter is the ability to marks areas in red for danger, yellow as caution and green for safe. These areas are visible at all zoom levels, making it easier to mark a shallow or rocks that you need to be aware of.

We use a B&G chart plotter on board RHO and the one feature I wish it had is this. I have found a work around, I create route around things I want to see regardless on the level of zoom and this includes Plateau des Minquiers.


The RYA Chart plotter is now an integral part of the RYA Day Skipper and RYA Coastal/Yachtmaster theory courses.  If you would like more information or would like to attend one of our courses in Central London, please contact us on 020 7002 7676 or email [email protected]


There is no additional info about this author.

Comments are closed.

There are no comment yet. Be the first to comment.