The chart plotter

Chart Plotter - Navigation system information from the RYA to help with your cruising navigation systems, find out more about chart plotters from the RYA

Electronic navigation must work hand in glove with traditional navigation techniques.

I am sadly coming to the conclusion that the chart plotter is marking the demise of traditional navigational knowledge; which is worrying. Traditional navigation and electronic means of navigation should go hand in hand at all times. 

This feeling came to me after watching a young but experienced seaman make a variety of basic errors whilst trying to establish his position.

Lost by a fix

After navigating to a waypoint using the plotter, he was asked to confirm the position by non- electronic means. He took a fix using a hand bearing compass, but it was evident that it was the first time he’d ever done so.

We were in an area where there were many identifiable points to choose from such as lighthouses, headlands, a breakwater and a handful of navigational marks. But the resultant fix was poor.

In fact, only two of the three lines crossed because there was less than 10 degrees angular difference separating the bearing lines. The narrow intersecting lines resembled a drawing of a road in perspective rather than a three point fix.

The second attempt was little better

This time the radar scanner was held for support, but being just six inches away from the hand bearing compass, it managed to deviate the bearings by about 30 degrees. So whilst we were only two miles offshore the fix was over half a mile out.

One last try and we got a reasonable fix. The three intersecting lines crossed with just a small but acceptable cocked hat appearing; no doubt due to the boat being motored slowly ahead in the swell for comfort.

When asked if any other information should be taken or logged with the fix; the question was answered with a blank stare. Usually, the time and a log reading are taken so that you know when you were in that position.

Secondary means of position fixing essential

Now I’m not suggesting that we need to go around taking a fix every five minutes, but it is essential to have a secondary means of position fixing at all times and that means having an understanding and knowledge of traditional navigation skills.

Especially as on board this boat the GPS system kept spiking out when the engines were started and the display would freeze from time to time.

Reliability of electrical equipment is a key problem facing the skipper and it is therefore essential to be able to back it up with your own position log plotted on your chart.

When taking a fix some points to remember are:

  • Pick identifiable and charted points about 60 -120° apart.
  • Pick objects close to you, if possible.
  • Take note of the time and log reading.
  • Beware magnetic, metallic or electrical influences.
  • Use a transit if possible.
  • Bearings abeam will change faster than those ahead of you.

Even simpler is the option of using nearby objects such as a buoy or a glance at the depth sounder to confirm that you are indeed where the plotter or GPS says you are.

The plotter is a great tool, nowadays the primary navigational tool, but basic navigation techniques must work hand in glove with it; particularly if the box of wizardry decides not to play one day.