How do you use a marine chartplotter to navigate safely?
I've just bought a 10-year-old Beneteau Oceanis with a Raymarine Axiom chartplotter at the helm. I'm used to paper charts and Navionics on my phone, but I want to get the most out of the dedicated plotter. What are the practical steps to set it up and actually use it under way?
Answer
To use a marine chartplotter effectively, start by configuring your boat's draught and safety clearances, then use it to monitor your real time position against vector chart data. The key is setting up a decluttered screen showing only essential data like depth, speed over ground (SOG) and cross track error (XTE) while you follow a preplanned route.
Setup and Safety Parameters
Before slipping your moorings, configure the plotter for your specific boat. Modern multifunction displays (MFDs) like the Raymarine Axiom, B&G Zeus or Garmin GPSMAP need your physical dimensions to keep you safe.
- Safety Depth: Set this to your actual draught plus a 0.5m safety margin. If your fin keel draws 1.8m, set the safety depth to 2.3m. The chartplotter will highlight waters shallower than this in a warning colour, usually dark blue or red.
- Alarms: Enable a shallow water alarm (typically set to 3m for coastal cruising) to give you time to react if you stray off course.
- Orientation: Set the chart to 'Heading Up' for tight pilotage so what you see on screen matches what is out the window. Use 'North Up' for general passage planning.
Managing Layers and Decluttering
Chartplotters use vector charts like Navionics, CMAP or Garmin BlueChart. These charts are built in layers, meaning the level of detail changes as you zoom in and out. Zooming out too far hides hazards like isolated rocks or drying patches.
A common mistake is sailing with a cluttered screen. Go into your chart settings and strip out data you do not need right now. Turn off seabed composition types, minor depth contours and complex light sector arcs during daylight hours. You want a clean display showing your boat icon, the route and major navigation marks. Enable tidal stream arrows if your chart card supports them. This gives a brilliant visual representation of real time set and drift.
Creating Routes and Waypoints
Plotting a route electronically is faster than on paper but requires the same seamanship. Drop waypoints at safe turning marks. Ensure you leave a wide berth around headlands, traffic separation schemes (TSS) and shallow banks.
- Manual Routing: Tap the screen to drop sequential waypoints, then save the route. When ready, select the route and hit 'Follow' or 'Track'.
- Auto Routing: Features like Navionics Dock to Dock are useful for roughing out a passage. Never follow an auto generated route blindly. Always review a generated route leg by leg at a high zoom level to ensure it does not drag you over a drying spit or through a firing range.