Navigation with No Instruments
Traditional techniques for navigating when electronics, GPS, and chartplotters fail.
COMPASS · LOG · CHART · OBSERVATION
When electronics fail, navigation returns to basics: steer a compass course, estimate speed, plot distance on a paper chart, and correct for wind and tide. Keep a written log at all times.
Dead Reckoning (DR)
Dead reckoning is the process of calculating your position from a known starting point, using your course steered and distance run. It does not account for wind or current — that comes later with Estimated Position.
Note Your Last Known Position
Start from your last confirmed fix — a GPS waypoint, a charted landmark bearing, or a harbour exit. Record the time on your log. This is your DR origin.
Record Course Steered
Read your steering compass and note the heading in degrees magnetic. Convert to true if your chart is true-north based: True = Magnetic + Variation (East is positive, West is negative).
Estimate Speed Through Water
Use your log (knotmeter) if working. If not, estimate from boat speed: watch bubbles or debris pass the hull and time them over a known length, or use the hull speed formula (1.34 × √waterline length in ft).
Calculate Distance Run
Distance = Speed × Time. At 5 knots for 1 hour, you cover 5 nautical miles. At 5 knots for 30 minutes, you cover 2.5 nm. Keep a log entry every 30–60 minutes.
Plot the DR Position
From your last position, draw a line on the chart in the direction steered, measured off the distance run. Mark the DR position with a semicircle and a cross, labelled with time.
Update Regularly
Repeat every 30–60 minutes, or after every course change. Each new DR position starts from the last one. Keep a written log: time, course, speed, distance, and position.
Estimated Position (EP)
Your DR position assumes you travel in exactly the direction you steer. In reality, wind (leeway) and tide (current) push you off course. The Estimated Position corrects for both.
Start from Your DR Position
Your Estimated Position (EP) begins where your DR left off. The EP accounts for factors DR ignores: leeway, current, and tide.
Estimate Leeway Angle
Leeway is the sideways drift from wind pushing the hull. In moderate wind, a typical cruising yacht makes 3–5° of leeway; in strong wind, 8–12°. Leeway pushes you downwind of your course.
Estimate Current / Tide Set & Drift
From your tidal atlas or local knowledge, determine the set (direction the current flows toward) and drift (speed in knots) for the period since your last position.
Apply Leeway to Course
Adjust your DR course by the leeway angle — downwind. If steering 090° with 5° leeway and wind from the north, your true track is 095°.
Plot the Tide Vector
From the end of your leeway-corrected DR line, draw a line in the direction of the tide set, measured off the tide drift × hours elapsed. The end of this line is your EP.
Mark the EP
Mark the EP with a triangle and label with time. The EP is your best estimate of position without electronic aids. Compare it with any visual bearings to check accuracy.
DR vs EP: What the Wind & Tide Do
Course × distance — ignores wind and tide
Wind pushes the hull sideways, downwind of course
DR + leeway + tide = best estimate of position
Taking Bearings on Landmarks
When you can see land, a hand-bearing compass and a paper chart give you an accurate visual fix — no electronics required.
Identify Two or Three Landmarks
Choose charted, identifiable features — headlands, lighthouses, towers, islands. Spread them as widely as possible (ideally 60–120° apart) for an accurate fix.
Take a Bearing on Each
Using a hand-bearing compass, sight each landmark and read the bearing in degrees magnetic. Note the time. Take bearings quickly to minimise position change between sights.
Convert to True Bearings
Add variation (East positive, West negative) to convert magnetic bearings to true. If you have a deviation card for your hand-bearing compass, apply that too.
Plot on the Chart
From each landmark, draw a line on the chart at the true bearing. Where the lines cross is your visual fix. Three bearings form a "cocked hat" — your position is within that triangle.
Use a Transit for a Quick Check
If two landmarks line up (a transit), you are somewhere on that line. Combine with one bearing for an instant fix — useful for harbour approaches and pilotage.
Time · Speed · Distance Formulas
Distance
Distance (nm) = Speed (kn) × Time (hours)
Example: 5 kn × 2 hrs = 10 nm
Speed
Speed (kn) = Distance (nm) ÷ Time (hours)
Example: 15 nm ÷ 3 hrs = 5 kn
Time
Time (hrs) = Distance (nm) ÷ Speed (kn)
Example: 20 nm ÷ 4 kn = 5 hrs
Minutes per Mile
60 ÷ Speed = minutes per nm
Example: 60 ÷ 5 = 12 min/nm
Compass, Variation & Deviation
Estimating Speed Without Instruments
Hull Speed Formula
Maximum theoretical speed for a displacement hull:
Speed (kn) = 1.34 × √(Waterline Length in ft)
e.g. 36 ft waterline → 1.34 × 6 = 8.0 kn max
Timed Pass Method
Time an object passing a known hull length:
Speed (kn) ≈ Length (ft) ÷ Time (s) × 0.59
e.g. 40 ft hull, object passes in 5 s → 4.7 kn
Practical Estimation & Observation Tips
Keep a Paper Log
A handwritten log is the heart of no-instrument navigation. Record entries every 30–60 minutes and after every course change.
| Time | Course (°M) | Speed (kn) | Distance (nm) | Leeway | Tide | Position |
|---|---|---|---|---|---|---|
| 0800 | 090 | 5.0 | — | 5° | 020/1.2 | Departed harbour |
| 0900 | 090 | 5.0 | 5.0 | 5° | 020/1.2 | DR + EP plotted |
| 1000 | 075 | 4.5 | 4.5 | 3° | 020/1.0 | Visual fix: headland |