Current triangle
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Current triangle  ·  Compass → chart

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

▶ CTW (input) ≈ Current (input) ✦ COG (calculated)
Try examples
Great Belt — northbound
Northbound with east-setting tidal current
CTW 350° STW 5 kn Current 2 kn E COG = ?
The Sound — southbound
Southbound with west-setting cross-current
CTW 175° STW 6 kn Current 2 kn W COG = ?
Cross-current NE
CTW E with north-setting cross-current
CTW 090° STW 5 kn Current 2 kn N COG = ?
Open sea
SSW with west-setting current
CTW 200° STW 7 kn Current 2 kn W COG = ?
Input
Course through the water (CTW)
Course read off / log course – track through the water
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 COG (SOG) CTW (STW) Current (drift)
✓
Course over ground
—
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)