Position Fixing & the Running Fix: A Sailor's Guide
GPS is brilliant — right up to the moment it isn't. This guide covers the traditional ways to know where you are: position lines, the three-bearing fix, transits, the running fix from a single object, and the difference between a dead-reckoning position and an estimated position.
Position lines and fixes
A position line is any line on the chart along which you know your boat lies. It might be:
- the bearing to a charted object (lighthouse, headland, beacon);
- a transit — two charted objects seen in line;
- a depth contour matched to your echo sounder;
- a distance off drawn as an arc (a circular position line).
One position line alone is not a fix — it only narrows you to that line. A fix is where two or more position lines, taken at the same time, cross. The better the crossing angle (toward 90°), the sharper the fix.
The three-bearing fix and cocked hat
The classic visual fix uses three compass bearings:
- Pick three charted objects spread around you, ideally 60–120° apart for clean crossing angles.
- Take each bearing in quick succession, then convert magnetic to true using the compass rose variation.
- Plot each as a line from its object; note the time and log.
Three bearings almost never meet at a single point — they form a small triangle called a cocked hat. A tight cocked hat means a good fix; take your position as the corner nearest any danger (the cautious assumption). A large cocked hat is a warning: a mis-identified object, a bearing error, or compass deviation to investigate.
Transits — the most accurate position line
A transit — two fixed charted objects lined up one behind the other — gives the single most accurate position line available, because it needs no compass and no instrument error. The moment two marks come into line, you are exactly on the line joining them on the chart. Transits are gold for checking compass deviation, marking a clearing line past a danger, and pinpointing the moment to alter course in pilotage.
The running fix
Sometimes only one charted object is in sight — a lone lighthouse on a featureless coast. A running fix turns that single object into a position:
- Take a bearing of the object; note the time and log. Plot it as a position line.
- Steer a steady course for a measured distance run.
- Take a second bearing of the same object; note time and log.
- Transfer the first position line forward, parallel to itself, by the course and distance run (allowing for tide and leeway).
- Where the transferred first line crosses the second bearing is your running fix.
Dead reckoning and estimated position
Between fixes you keep track of where you are by calculation:
- Dead reckoning (DR) — from your last fix, apply course steered and distance run through the water. No tide, no leeway. It's the bare skeleton of your track.
- Estimated position (EP) — take the DR and apply the tidal stream (set and rate) and any leeway from the wind. The EP is your best estimate of where the boat actually is.
Work up a DR/EP regularly so that if the GPS fails you already have a recent, trustworthy position to navigate from.
Plotting symbols
| Symbol | Meaning |
|---|---|
| Dot inside a circle, with time | Fix — a confirmed position from crossing position lines |
| Dot with a single cross-bar, with time | Dead reckoning (DR) position |
| Dot inside a triangle, with time | Estimated position (EP) |
| Arrow on a course line | Water track / course steered; tidal vector drawn separately |
Why learn this with GPS aboard
Electronic navigation is the primary method on almost every modern boat — and rightly so. But antennas fail, batteries die, software hangs and the wrong waypoint gets entered. Traditional fixing lets you cross-check the plotter, keep going when it stops, and — most importantly — hold a mental picture of where you are and what's around you, instead of trusting a single moving dot. Every recognised skipper syllabus teaches it for exactly this reason.
Frequently asked questions
What is a position line?
A line on the chart along which you know you lie — a bearing to a charted object, a transit, or a depth contour. A single position line isn't a fix; cross two or more taken at the same time to get a fix.
How do you take a three-point fix?
Take compass bearings of three charted objects spread 60–120° apart, convert to true, and plot each as a position line. They form a small triangle (cocked hat); take the corner nearest danger as your position.
What is a running fix?
A way to fix position from one object: take a bearing, run a known course and distance, take a second bearing, then transfer the first position line forward by the run. Where it crosses the second bearing is the fix.
What is the difference between DR and EP?
A dead-reckoning position uses only course steered and distance run through the water. An estimated position adds the tidal stream and leeway, giving a more realistic position. EP is the better estimate between fixes.
Related reading
- How to Read Nautical Charts — scale, the lat/long grid and measuring distance
- Understanding Tides — tidal streams that shift your EP
- Free sailing video lessons — chartwork, position fixing and more
- Maritime glossary — navigation and COLREG terms
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