Modern Navigation: Putting It Together
Integrating GPS, chartplotters, and electronic tools for safe coastal passages
Pre-Departure: Electronic Route Setup
Modern coastal navigation begins with route planning on the chartplotter. Enter your waypoints from departure to destination, either by selecting them on the electronic chart or by keying in latitude and longitude coordinates directly. As you build the route, the plotter will display the course and distance for each leg, total distance, and — if you enter an estimated speed — the estimated time en route. Review each leg carefully on the screen, zooming in to confirm that no leg crosses shallow water, restricted areas, or charted obstructions. The convenience of electronic planning makes it tempting to rush, but errors in waypoint entry can send you directly toward hazards.
Before departure, verify the chart database currency. Electronic charts are updated regularly, and an outdated database may not show recent changes — new buoys, altered shipping lanes, or newly surveyed shoals. Check the edition date and apply any available updates. Also confirm that the chart datum matches your GPS datum (virtually all modern systems use WGS 84, but older charts or regional databases may differ). A datum mismatch can offset your displayed position by hundreds of meters — more than enough to put you on the rocks.
Configure your AIS display to show traffic in the area and set appropriate alarms: anchor watch (if applicable), cross-track error (XTE) alarm, shallow water alarm, and waypoint arrival alarm. AIS will display other vessels' names, courses, speeds, and closest points of approach (CPA), giving you early warning of potential collision situations. Test all alarms before departure — an alarm that fails to sound is worse than no alarm at all, because it creates false confidence.
Always save your planned route and back it up to a second device (a tablet, laptop, or SD card). If the primary chartplotter fails, you can reload the route on a backup unit without re-entering every waypoint from scratch.
Departure: Verifying Electronics Against Reality
As you leave the harbor, the first task is to verify that the electronics agree with what you see. Check the GPS position on the chartplotter against your visual departure position — the fix should show you at or very near the harbor entrance, consistent with the landmarks you can identify. If the GPS places you 200 meters inland or in the middle of a breakwater, something is wrong: a datum issue, a chart offset, or a GPS error. Do not leave the harbor until the electronic position matches reality.
Compare the electronic course displayed on the chartplotter to the magnetic compass heading you are actually steering. They should agree within a few degrees (after accounting for variation and any known deviation). If the chartplotter shows a course of 095°T and your compass reads 110°C, but variation is only 5°W and deviation is 2°E, the numbers do not add up — investigate before relying on either one. This cross-check catches compass errors, chartplotter configuration mistakes, and heading sensor calibration issues all at once.
Watch the chartplotter track as you motor or sail out of the harbor. The track trail — the line showing where you have been — should follow the channel and match your visual sense of the route. If the track wanders onto land or into areas you know you did not transit, the electronic chart may be offset from reality. Note the discrepancy in the logbook and be alert for further inconsistencies as you proceed. This departure verification is the electronic equivalent of the traditional departure fix — it establishes that your primary navigation system is trustworthy before you depend on it.
Never assume the electronics are correct simply because they display a position confidently. GPS can show a precise-looking fix that is actually offset due to datum errors, multipath reflections from nearby structures, or even deliberate signal interference. Always cross-check with visual references at departure.
At departure, your chartplotter shows your position 150 meters inland from the dock where you are physically standing. The most likely cause is:
Why should you compare the chartplotter course to the magnetic compass heading at departure?
Underway Electronic Navigation
Once established on the route, the chartplotter becomes your primary navigation display. The key parameter to monitor is cross-track error (XTE) — the perpendicular distance between your actual position and the planned track line. Most chartplotters display XTE numerically and graphically. Keep XTE within your chosen tolerance (typically 0.1 NM in open water, tighter in restricted channels). If XTE creeps up, adjust your heading to steer back toward the track line. Many plotters offer a 'highway' display mode that makes XTE deviations immediately obvious.
Monitor waypoint approach information: distance to the next waypoint, bearing to the waypoint, estimated time of arrival, and the course change required at the waypoint. Most systems sound an alarm when you enter the waypoint arrival circle (a configurable radius around the waypoint). When the alarm sounds, confirm visually that you are where the plotter says, execute the course change to the next leg, and verify that the new course and XTE are correct. Also watch the AIS traffic display continuously — other vessels' CPA and TCPA (time to closest point of approach) tell you which targets need your attention for collision avoidance.
Use the depth overlay on the chartplotter as a continuous position cross-check. If the chart shows 15 meters under your track but the depth sounder reads 8 meters, your position may not be where the plotter indicates — or the chart may be based on an old survey. In either case, the disagreement demands investigation. Depth is an independent data source that does not rely on GPS, so it provides a valuable sanity check. Log your position, course, and speed at regular intervals even when using electronics — the logbook remains your backup record if the electronics fail.
Set your XTE alarm to a value appropriate for the waters you are transiting. In a narrow channel, 0.05 NM (about 90 meters) may be appropriate. In open coastal water, 0.2 NM allows for normal course variations without constant alarms.
When Electronics and Eyes Disagree
The most dangerous moment in electronic navigation is when the chartplotter shows one thing and your eyes show another. You see breaking water ahead, but the chart shows deep blue. The plotter says you are in the middle of the channel, but the buoys are clearly off to one side. The displayed depth reads 20 meters, but you can see the bottom through the clear water. These disagreements are not rare — and how you handle them determines whether the passage ends safely.
There are several common causes of electronic/visual disagreement. Chart datum issues can offset the entire chart by tens or hundreds of meters relative to GPS positions. Old hydrographic surveys may not reflect current bottom conditions — sandbars shift, new wrecks appear, and charted depths in poorly surveyed areas may be based on century-old leadline soundings. Display errors can arise from corrupted chart files, incorrect chart selections (wrong scale, wrong area), or software glitches that misrender features. In every case, the underlying principle is the same: the electronic chart is a model, not reality.
The rule for close-quarters situations is unequivocal: trust your eyes over the electronics. If you can see a hazard that the chart does not show, the hazard is real regardless of what the screen displays. Slow down, increase your lookout, take visual bearings, and if necessary take soundings with a lead line. Report charted errors to the hydrographic authority after the passage. The chartplotter is a magnificent tool, but it is not infallible — the navigator who remembers this is the one who avoids the reef that the chart forgot to show.
Never drive into water that looks wrong because the chartplotter says it is safe. Electronics display data, not truth. If visual evidence contradicts the screen, the visual evidence takes priority — always.
Your chartplotter shows 12 meters of depth under your keel, but you can clearly see a sandy bottom through the water and your depth sounder reads 3 meters. You should:
Which of the following is NOT a common cause of disagreement between the chartplotter display and visual observation?
Integrating Traditional and Electronic Methods
The best navigators do not choose between traditional and electronic methods — they use both simultaneously, each covering the other's weaknesses. GPS provides continuous, accurate position data that no human can match for speed and consistency. Traditional methods provide independent verification, situational awareness, and a fallback when electronics fail. The goal is integration: use the GPS position to speed up visual fix confirmation, and use visual fixes to confirm that the GPS is telling the truth.
Maintain a paper logbook even on a fully electronic bridge. Record positions, courses, speeds, and weather observations at regular intervals — every 30 minutes in coastal waters is good practice. If all electronics fail simultaneously (a lightning strike, a power bus failure, a flooded nav station), the logbook and the paper chart give you an immediate starting point for traditional navigation. Periodically — once an hour, or at every course change — take a manual visual fix and compare it to the GPS position. If they agree within a few hundred meters, you have high confidence in both systems. If they disagree, investigate immediately.
This integrated approach also sharpens your skills. Navigators who rely exclusively on the chartplotter gradually lose the ability to take quick, accurate visual bearings and plot them on a chart. When the day comes that they need those skills — and it will come — they may find them rusty. Regular practice of traditional methods alongside electronic navigation keeps skills sharp, builds confidence, and creates a navigator who is genuinely competent in all conditions rather than merely competent when the power is on.
A good drill: at each course change, take a quick three-bearing visual fix and plot it on the paper chart before looking at the GPS position. Then compare. Over time, this builds both speed and confidence in your traditional piloting skills.
Electronic Navigation in Degraded Conditions
Electronic navigation systems work flawlessly until they do not — and the failure often comes at the worst possible moment. Screen visibility degrades dramatically in heavy rain, direct sunlight, or spray. Many chartplotter screens become nearly unreadable in bright conditions without a hood or shade, and wet screens may register phantom touch inputs. Night mode helps in darkness but does not solve daytime glare. Know your equipment's limitations and have a backup display method: a tablet in a waterproof case, a dedicated GPS handheld, or the paper chart already set up.
Power management is critical on long passages. A full chartplotter, radar, and AIS installation can draw 5 to 15 amps continuously — a significant load on a sailing vessel's battery bank. Monitor voltage and consumption, and have a plan for reducing load if charging fails. GPS receivers themselves draw very little power, but the displays and processors they feed are power-hungry. A handheld GPS with lithium batteries is an excellent low-power backup that can run for 20+ hours independently of the ship's electrical system.
Plan for GPS dropout. While rare, GPS signal loss can occur due to atmospheric conditions, antenna problems, or (in some regions) intentional jamming. If the GPS position freezes, jumps erratically, or the unit displays a 'no fix' warning, you must transition to backup navigation immediately. Note the last good GPS position, time, course, and speed. Begin a manual DR from that point. Take visual fixes if landmarks are available, or use depth contours and radar ranges to estimate position. The transition from electronic to traditional navigation should be practiced before you need it — the middle of a rainstorm in a shipping lane is not the time to learn.
If your GPS position suddenly jumps by a large amount (miles, not meters) or shows an impossible speed, do NOT trust the new position. The system may have acquired a false fix. Revert to the last known good position and begin DR until the GPS stabilizes or you can confirm position by other means.
Your GPS display shows 'No Fix' while you are 5 miles offshore in fog. Your first action should be:
A handheld GPS is recommended as a backup primarily because:
Summary
Modern electronic navigation begins with careful route planning on the chartplotter — verifying waypoints, chart database currency, datum settings, and alarm configurations before departure.
At departure, verify electronics against reality by comparing the GPS position, chartplotter track, and electronic course to visual references and the magnetic compass.
Underway, monitor XTE, waypoint approach, AIS traffic, and depth overlay continuously, but always maintain a paper logbook and take periodic manual fixes as independent cross-checks.
When electronics and eyes disagree, trust your visual observations in close quarters — the electronic chart is a model built from data that may be outdated, offset, or corrupted.
Integrating traditional and electronic methods provides the highest level of navigational safety: GPS for precision and speed, traditional skills for independence and verification.
Key Terms
- Cross-Track Error (XTE)
- The perpendicular distance between the vessel's actual GPS position and the planned track line. Monitoring XTE ensures the vessel stays on the intended route.
- Chart Datum
- The reference coordinate system used to define positions on a chart. A mismatch between the chart datum and the GPS datum (typically WGS 84) can offset displayed positions by significant distances.
- AIS (Automatic Identification System)
- A system that broadcasts and receives vessel identity, position, course, and speed data, enabling collision avoidance and traffic awareness on the chartplotter display.
- CPA / TCPA
- Closest Point of Approach and Time to Closest Point of Approach — AIS-calculated values predicting how close another vessel will pass and when, used for collision risk assessment.
- Waypoint Arrival Circle
- A configurable radius around a waypoint that triggers an alarm and/or automatic course change when the vessel enters it, signaling the transition to the next route leg.
- GPS Dropout
- The loss of GPS satellite fix due to antenna problems, signal interference, atmospheric conditions, or jamming — requiring immediate transition to backup navigation methods.