Current triangle in brief
Set and drift describe how a current affects your passage:
- Set: direction the current pushes you
- Drift: strength of the current (often in knots)
From course through water and current you get course over ground (COG) — or the reverse when you know the COG you want and need the steering course.
The current triangle is the classic graphic solution; digitally you run the same logic in seconds — offline on iPhone.
When you need the current triangle
- Passage planning: current from atlas, tide table, or estimate
- Underway: explain or correct deviation from the chart line
- Training: understand COG vs. course through water (CTW)
The full course chain (rwK, mwK, MgK plus wind) is under Course correction. Current only: Current correction.
Known: course and speed through water — find COG
Typical inputs:
- CTW (course through water) and speed through water
- Set and drift
Result: COG and speed over ground (SOG) — important for ETA and chart checks.
Known: COG — find steering course
You want to hold a line over the ground:
- COG and SOG (or desired SOG)
- Set and drift
Result: which CTW to steer — then continue the chain to MgK (variation, deviation).
Where set and drift come from
| Source | Note |
|---|---|
| Current atlas / chart | Planning before departure |
| Tidal stream | HW/LW window, pick the station |
| Estimate on site | Local experience |
| GPS over time | COG vs. CTW — plausibility check |
NauticCalc provides the calculator, not live current charts. You enter values you stand behind for the leg.
Current vs. full course correction
| Topic | Current correction / triangle | Course correction (hub) |
|---|---|---|
| Focus | Set, drift, triangle | rwK, mwK, MgK, wind, current |
| Audience | “Only current math” | Full navigation flow |
Both pages link to each other on purpose — to avoid duplicate content.
Typical mistakes
- Set confused with arrow direction on the chart — read the symbol carefully
- Drift in km/h instead of kn — check units
- Current applied twice (triangle plus wrong entry in the chain)
- GPS SOG confused with speed through water when checking
Use offline
Current and course calculators in NauticCalc run without a network. Ideal on the bridge when you take values from planning or the current atlas.
→ Offline navigation · Plan ETA
Bottom line
The current triangle stays a core piece of traditional navigation. Digitally you save time and sign errors — provided set and drift are plausible. Keeping current math and the course chain separate keeps you in control.
Read next: Current correction · Course correction step by step · Course correction