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Electronic Navigation: Trust, but Cross-Check
💡 Electronics answer different questions and can fail silently — always cross-check position against your independent DR plot and a depth reading.
Modern boats bristle with electronics, but each answers a different question. GPS tells you where you are (a latitude/longitude fix accurate to a few metres). The chart plotter shows that fix on an electronic chart with your COG (course over ground) and SOG (speed over ground). AIS (Automatic Identification System) shows other vessels' names, courses and speeds, flagging any on a collision course. Radar detects physical objects — ships, buoys, squalls, coastlines — including things AIS can't see, like a small yacht with no transponder or a rock.
The golden rule: electronics fail silently or lie plausibly. A GPS can lose signal, a plotter can run an outdated chart, AIS only shows transmitting vessels, and radar returns need interpreting. This is why the DR (dead reckoning) plot you built in earlier cards still matters: it's your independent prediction from course, speed and time. If the plotter says you're 2 miles from where your DR expects, one of them is wrong — and finding out which before you hit something is the whole point.
Use each tool for what it does best and layer them. Radar plus AIS together identify targets and confirm collision risk; GPS plus plotter give position; DR plus a quick compass and depth check confirm the electronics are honest. A depth sounder reading 5 metres when the chart says 30 is a louder warning than any screen.