Boating Navigation Basics: Charts, GPS, and Rules of the Road

Updated April 2026 · By the BoatCalcs Team

Modern GPS makes it easy to navigate from point A to point B, but it does not tell you about submerged rocks, shallow shoals, restricted zones, or the rules that determine who has the right of way when two boats converge. Navigation is a fundamental seamanship skill that every boat operator should master, not just for passing a boating safety course, but because GPS batteries die, screens glare in sunlight, and electronic charts have errors. This guide covers the navigation knowledge that keeps you safe and legal.

Reading a Nautical Chart

Nautical charts are maps of the water showing depth soundings, bottom types, navigation aids, hazards, channels, and restricted areas. Depths are shown as numbers scattered across the water area, measured in feet or fathoms (6 feet) at mean lower low water (the average of the lower of the two daily low tides). This means actual depth at high tide is deeper than charted.

Contour lines (depth curves) connect points of equal depth. Closely spaced contour lines indicate a steep underwater slope. Widely spaced lines indicate a gradual slope. Color coding helps: white or pale blue is navigable water, darker blue or green indicates shallow areas, and tan or brown is dry land or areas that expose at low tide.

The US Aids to Navigation System

The IALA-B buoy system used in US waters follows the Red Right Returning rule: when returning from sea (entering a harbor or heading upstream), keep red markers on your right (starboard) side. Red markers are even-numbered. Green markers are odd- numbered and go on your left (port) side when returning.

Channel markers define the navigable path. Red nuns (pointed tops) and green cans (flat tops) mark channel edges. Red-and-green horizontally striped markers indicate the middle of the channel or a junction. Yellow markers indicate special areas like anchorages, cable crossings, or restricted zones. Day shapes (diamond, circle, square) on white markers indicate specific regulations.

GPS Navigation: Using It Wisely

A GPS chartplotter shows your position on an electronic chart in real time. It can create routes with waypoints, calculate ETA and fuel needs, and display speed, heading, and track history. Modern units integrate AIS (Automatic Identification System) to show nearby commercial vessel positions.

The critical limitation of GPS is that it cannot see the water. Electronic charts may have errors, especially in less-surveyed areas. GPS routes drawn on a chart do not account for current, wind, or traffic. Never follow a GPS route without also monitoring your surroundings visually and cross-referencing with paper charts in unfamiliar waters.

Navigation Rules: Who Goes First

The COLREGS (International Regulations for Preventing Collisions at Sea) define the rules. In a head-on situation, both vessels alter course to starboard (right). When two power vessels cross, the vessel on the right has the right of way (the stand-on vessel) and the other must yield (the give-way vessel).

Sailboats under sail have right of way over power vessels in most situations, except when overtaking, in a narrow channel, or near commercial vessels in shipping lanes. Every vessel, regardless of right of way, is required to take action to avoid a collision. Right of way does not mean immunity from responsibility.

• Head-on: both vessels turn right (starboard)
• Crossing: vessel on the right is stand-on, other yields
• Overtaking: overtaking vessel must stay clear of the vessel ahead
• Sail vs power: sail generally has right of way with exceptions
• Always: take action to avoid collision regardless of right of way

Planning a Safe Course

Before leaving the dock, plot your route on a chart (paper or electronic). Identify hazards along the way: shallow areas, rocks, restricted zones, and crossing traffic lanes. Note the locations of safe harbors along the route in case weather deteriorates. Check the weather forecast and tide tables.

File a float plan with a responsible person who is not going on the trip. Include your departure and expected return time, route, vessel description, number of passengers, and emergency contact numbers. If you do not return on time, this plan enables a targeted search rather than a random one.