Navigation — Staircase Method

The staircase method converts between four course types. The rule is simple:

• Going up (Compass → Water): ADD
• Going down (Water → Compass): SUBTRACT

The Staircase

┌──────────────────────────────────────────────────┐
│  KV  — Water Course     (Kurz vůči vodě)         │
│        ↑ + drift         ↓ − snos                │
│  KR  — True Course      (Pravý kurz)             │
│        ↑ + variation     ↓ − variace             │
│  KM  — Magnetic Course  (Magnetický kurz)        │
│        ↑ + deviation     ↓ − deviace             │
│  KK  — Compass Course   (Kompasový kurz)         │
└──────────────────────────────────────────────────┘

Signs

• W (West) var/dev → negative value
• E (East) var/dev → positive value

Variation (var)

Variation is the angle between True North and Magnetic North. Always update it from the chart for the current year:

Current var = Base var ± (annual change × years elapsed)

Example: Base 5°35’ W in 2018, annual change 6’ W, year 2023:

var = 5°35' + (5 × 6') = 5°35' + 30' = 6°05' W ≈ −6°

KK → KV (Compass to Water — going UP, ADD)

KM = KK + dev
KR = KM + var
KV = KR + snos

Example: KK = 261°, dev = 0°, var = −6°, wind from starboard (snos = −4°)

KM = 261° + 0°   = 261°
KR = 261° + (−6°) = 255°
KV = 255° + (−4°) = 251°

KV → KK (Water to Compass — going DOWN, SUBTRACT)

KR = KV − snos
KM = KR − var
KK = KM − dev

Example: KR = 346°, dev = 0°, var = −6°

KM = 346° − (−6°) = 352°
KK = 352° − 0°    = 352°

Drift (snos)

Drift is the sideways push of the wind on the boat, shifting the water course from the true course.

Bearings

The same staircase applies when converting compass bearings to true bearings for chart plotting:

True bearing = Compass bearing + dev + var

Plot two or more true bearings on the chart — their intersection is your estimated position.

Distance & Speed

Distance (NM) = Speed (kts) × Time (min) / 60
Time (min)    = Distance (NM) × 60 / Speed (kts)

Example: Speed = 3 kts, Time = 90 min

Distance = 3 × 90 / 60 = 4.5 NM

ETA

ETA = departure time + travel time
travel time (min) = Distance × 60 / Speed

Example: Depart 16:00, distance = 9.6 NM, speed = 3 kts

travel time = 9.6 × 60 / 3 = 192 min = 3h 12min
ETA = 16:00 + 3:12 = 19:12

Converting Compass Bearing to Chart Bearing (Position Fix)

When you sight a landmark with a hand bearing compass, the reading is a compass bearing. To plot it on a nautical chart (which uses true north) you must convert it using the same staircase.

Steps

1. Sight the landmark with the hand bearing compass → get compass bearing
2. Convert to true bearing (go UP, ADD):

   True Bearing = Compass bearing + dev + var
   

3. Plot on chart: from the landmark, draw a line in the reciprocal direction (true bearing ± 180°) — you are somewhere along this line
4. Repeat for a second (and ideally third) landmark
5. Intersection of the lines = your position fix

Example

Compass bearing to lighthouse = 043°, dev = 0°, var = −6°

True Bearing = 043° + 0° + (−6°) = 037°
Reciprocal   = 037° + 180°        = 217°

Draw a line from the lighthouse at 217° on the chart. You are on that line.

Tips

• Use 3 bearings when possible — if they form a small triangle (cocked hat), your position is inside it
• Choose landmarks roughly 60–120° apart for the best intersection angle
• Bearings to objects ahead or astern are less reliable — prefer objects to the side
• Take all bearings quickly to minimise error from boat movement

Measuring Compass Deviation

Deviation is caused by the boat’s own magnetic field (engine, wiring, steel fittings). It varies with heading and must be measured for each compass on each boat.

Formula

dev = True Course − var − KK

Where True Course comes from GPS, a transit, or a known bearing.

Method 1: GPS Comparison (easiest)

Modern GPS units show COG (Course Over Ground) in true degrees.

Requirements: calm water, no current, no wind (so the boat tracks straight — leeway = 0).

Steps:

1. Motor (not sail — sails cause leeway) on a steady heading
2. Note the compass heading (KK)
3. Read the GPS COG (= True Course)
4. Calculate deviation:

   dev = GPS COG − var − KK
   

5. Repeat on at least 8 headings (N, NE, E, SE, S, SW, W, NW)
6. Record results in a deviation table

Example: KK = 090°, var = −6°, GPS COG = 087°

dev = 087° − (−6°) − 090° = 087° + 6° − 090° = +3°E

Method 2: Transit / Leading Lines (most accurate)

A transit is two charted objects that line up — their true bearing is known from the chart.

Steps:

1. Find two charted objects that form a transit (e.g. lighthouse and church spire)
2. Look up or calculate the true bearing of the transit from the chart
3. Motor until both objects are exactly in line
4. Note the compass heading at that moment
5. Calculate:

   dev = True Bearing − var − Compass reading
   

Advantage: No GPS needed, very precise.

Method 3: Reciprocal Bearings

Use a hand bearing compass (minimally affected by ship’s magnetism) as a reference.

Steps:

1. Anchor or stop the boat
2. Send a person ashore with the hand bearing compass
3. Both take bearings to each other simultaneously
4. The two bearings should differ by exactly 180°
5. Any difference is deviation in the steering compass

Deviation Table

After measuring on multiple headings, record the results:

Interpolate between measured headings for any course in between.

Tips

• Deviation changes if you add/move metal objects, electronics, or speakers near the compass
• Remeasure after any significant modification to the boat’s equipment
• A deviation of less than ±3° is generally acceptable for coastal sailing
• Steer clear of metal objects and active electronics when taking compass readings

Quick Reference