Current triangle
Navigation tool

Current triangle  ·  Chart → compass

Know your course over ground and the current – automatically calculate the course through the water (CTW) and speed over ground (SOG). The triangle updates live as you change the input.

▶ COG (input) ≈ Current (input) ✦ CTW (calculated)
Try examples
Little Belt
Course E with north-setting current
COG 090° STW 5 kn Current 2 kn N CTW = ?
Great Belt
North with east-setting current
COG 000° STW 6 kn Current 1,5 kn E CTW = ?
Aarhus Bay
West with south-setting current
COG 270° STW 5 kn Current 1 kn S CTW = ?
Strong cross-current
South with strong westerly current
COG 180° STW 5 kn Current 3 kn W CTW = ?
Input
Course over ground (COG)
Course taken from the chart / planned course over ground
Speed through the water (STW)
Log reading – speed relative to the water
Current – direction and strength
current strength
Current triangle – live
N S SOG — kn No solution – current too strong COG (SOG) CTW (STW) Current (drift)
⚠ No solution: the current is too strong relative to STW – the course cannot be held.
✓
Course through the water
—
SOG: — knots

Understanding the triangle

COG – Course over ground / track over the seabed (magnitude = SOG)
CTW – Course through the water / track through the water (magnitude = STW)
Current – Direction and strength of the current (drift in knots)