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Aids to navigation

Aids to navigation, such as GPS, radar and chartplotters, are just that – aids to navigation. As a responsible skipper, it is essential to keep a proper lookout at all times. You must also plan for the unexpected, for example your electronics failing after your battery goes flat, or after a small fire.

The level of skill and navigation equipment required will depend on the type of boat you have and how far you go from shore.

The following navigational aids can assist in making navigation a lot easier, and are a great means of double-checking or confirming your chartwork. However, these aids will always only complement a boating education course, charts, compass and using your eyes.

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GPS/Chartplotters

GPS (Global Positioning System) gives you an accurate position, but to use it you will need to carry the correct chart and understand how longitude and latitude are marked.

The GPS also displays other useful information, so make sure you read the owner’s manual to ensure your GPS is set up correctly and you fully understand it.

There are seven “golden rules” for using your GPS:

1. Make sure you have entered the correct datum into your GPS.
2. Check the chart title for any datum corrections.
3. Lay off safe ground tracks on a paper chart and check for hazards.
4. Check the accuracy of waypoints taken off the chart, and check them again after entering them in your GPS.
5. At regular intervals, plot your GPS positions on a paper chart.
6. Remember that old charts of the southwest Pacific can be several miles out.
7. Watch your GPS screen for high HDOP (horizon dilution of precision) and warnings of outages.

Radar

Radar is a system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects, such as other vessels, weather formations and terrain.

Marine radar systems can provide very useful navigation information. When the vessel is within radar range of land or special radar aids to navigation, the navigator can take distances and bearings to charted objects and use these to establish arcs of position and lines of position on a chart. A fix consisting of only radar information is called a radar fix.

Some types of radar fixes include the relatively self-explanatory methods of "range and bearing to a single object”. Radar, like GPS is an excellent aid to navigation that can be used to confirm or double check your chart work.

Echo (depth) sounders or depth finder

Echo sounders, depth sounders, depth finders and fathometers all do the same thing – they display the depth of water – and should be switched on at all times.

They use exactly the same principal as radar to measure the depth of the water beneath any vessel. Sonic pulses are projected down to the seabed, which reflect them and return them as echoes. The pulses are transmitted and received through a transducer, which is either fitted inside or on the underside of the hull.

By measuring the time span between the transmission of each pulse and the returning echo, the depth is calculated. This depth is displayed on an analogue or digital indicator on your vessel, usually near the helm.