Visual Bearing Fix
Pinpointing Your Position with Compass Bearings to Charted Objects
What Is a Visual Bearing Fix?
A visual fix uses compass bearings to two or more charted objects — lighthouses, beacons, towers, headlands — to establish your position on the chart. Each bearing produces a line of position (LOP), and the intersection of two or more LOPs marks your fix. This is one of the oldest and most reliable methods of coastal navigation, requiring nothing more than a hand-bearing compass and a chart.
For best accuracy, choose objects separated by 60-120 degrees — close to 90 degrees apart is ideal. When two LOPs cross at a shallow angle the intersection becomes elongated and uncertain, making it difficult to determine your true position. With three bearings, the LOPs form a small triangle called a cocked hat; your position lies somewhere inside that triangle, and a smaller cocked hat indicates a more accurate fix.
Transits (ranges) are even more precise than compass bearings because they do not depend on the compass at all. When two charted objects line up visually, you know you are somewhere along the line connecting them. Combining a transit with a single compass bearing gives an excellent two-LOP fix with very high confidence.
Always take the bearing to the object that is changing most slowly first (usually the one closest to the beam), then take the bearing to the object changing most quickly (usually the one closest to ahead or astern). This minimizes the time error between sights.
Never rely on a fix from only two bearings that cross at less than 30 degrees. The resulting position can be wildly inaccurate due to even small bearing errors.
What is the ideal angular separation between two landmarks used for a visual bearing fix?
What is the small triangle formed by three LOPs called?
Taking Compass Bearings
The most common instrument for visual bearings is the hand-bearing compass. To take a bearing, hold the compass at eye level, sight across the lubber line or through the prism at the target object, and read the bearing from the compass card once the card has settled. Brace yourself against the boat's motion — wedge your elbows against your body or lean against the companionway to hold steady. Read the bearing to the nearest degree if possible, and always record the bearing immediately along with the exact time.
Some vessels use a pelorus or azimuth circle mounted on the steering compass to take bearings. The advantage is that the pelorus is fixed to the vessel's centerline, eliminating the wobble of a hand-held compass. However, pelorus bearings are relative to the ship's head and must be converted to compass bearings by adding the vessel's heading at the instant the bearing was taken.
Regardless of which instrument you use, take bearings in quick succession to minimize the position change between sights. On a vessel moving at 6 knots, you travel 100 meters per minute, so a delay of even 30 seconds between bearings can introduce meaningful error. Record each bearing with its time to the nearest minute, the compass heading of the vessel, and the log reading if available.
In rough weather, take three readings of each bearing in quick succession and average them. This smooths out the effect of the vessel's yawing motion on your compass reading.
Keep the hand-bearing compass well away from metal fittings, electronics, and magnetic objects. Even a belt buckle or a steel guardrail can deflect the compass card by several degrees.
Selecting Landmarks
Not every visible object makes a good bearing target. The landmark must be positively identifiable — you must be certain which charted feature you are looking at. A lighthouse with a distinctive daymark or light characteristic is ideal; a vague stretch of coastline is not. Before entering coastal waters, study the chart and the cruising guide to identify which landmarks will be available along your route.
Choose objects that are charted with a precise position. A church spire, a radio tower, or a navigation beacon has a single plotted point on the chart. A long headland or a broad island has no single point, and different observers might sight different parts of it, leading to inconsistent bearings. When using a headland, sight the most prominent tip or the highest point, and note which feature you used.
Angular spread is critical. Select landmarks so that the bearings are separated by at least 60 degrees and ideally close to 90 degrees for a two-bearing fix, or approximately 120 degrees apart for a three-bearing fix. If you cannot find well-separated objects, supplement your bearings with a depth sounding or a transit to strengthen the fix. Always have a backup plan in case a landmark becomes obscured by haze, rain, or the vessel's own rigging.
Before your passage, mark potential bearing targets on your chart with a highlighter. This saves time when you are on deck in challenging conditions and need to identify landmarks quickly.
Plotting the Fix and Common Errors
To plot a visual fix, first convert each compass bearing to a true bearing by applying variation (from the chart's compass rose) and deviation (from your vessel's deviation card). Remember the mnemonic: Compass to True — Add West (CADET: Compass ADd East for True, when going from compass to true, add easterly errors). Mark each landmark on the chart, place a parallel rule or plotter on the landmark aligned to the corrected true bearing, and draw the LOP through the landmark.
Where two LOPs cross, mark the intersection with a small circle and dot — this is your fix. Label it with the time (using the 24-hour clock) and draw a small circle around the dot. If you have three LOPs and they form a cocked hat, place your fix at the corner of the triangle closest to any danger. This conservative approach ensures that if your position is anywhere within the cocked hat, you have allowed for the worst case.
The most common errors in visual bearing fixes are: misidentification of landmarks (sighting the wrong object), compass errors not properly corrected (forgetting deviation or applying variation in the wrong direction), excessive time between bearings (the vessel moves significantly between sights), and poor angular separation (bearings too close together). Developing a systematic routine — identify, sight, read, record, plot — minimizes these mistakes. Practice the full procedure in calm conditions until it becomes second nature.
Always double-check that you have applied variation and deviation in the correct direction. A sign error can shift your plotted position by miles.
When three LOPs form a cocked hat near a navigational hazard, where should you place your fix?
What must you apply to a compass bearing before plotting it on a chart that uses true north?
Summary
A visual bearing fix uses compass bearings to two or more charted landmarks to establish your position where the lines of position intersect.
Choose landmarks that are positively identifiable, precisely charted, and separated by 60-120 degrees for best accuracy.
Take bearings quickly in succession, starting with the object changing most slowly, and record each with the exact time.
Convert compass bearings to true bearings by applying both variation and deviation before plotting on the chart.
When three LOPs form a cocked hat near danger, place your fix at the corner closest to the hazard as a safety measure.
Practice the full procedure — identify, sight, read, record, plot — until it becomes second nature.
Key Terms
- Line of Position (LOP)
- A line on the chart along which the vessel's position is known to lie, derived from a single observation such as a compass bearing.
- Cocked Hat
- The small triangle formed when three lines of position do not meet at a single point, indicating minor observational errors. The vessel's true position is assumed to lie within this triangle.
- Hand-Bearing Compass
- A portable, hand-held compass used to take bearings to landmarks or other vessels independently of the ship's steering compass.
- Variation
- The angular difference between true north and magnetic north at a given location, caused by the Earth's magnetic field. Found on the chart's compass rose.
- Deviation
- The error in a magnetic compass caused by the vessel's own magnetic influences such as engines, electronics, and metal fittings. It varies with the vessel's heading.
- Transit (Range)
- An alignment of two charted objects that produces a highly accurate line of position without requiring a compass reading.