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What are COG and SOG?
March 6, 2026 · 6 min · 1K views
What this video covers
COG (Course Over Ground) and SOG (Speed Over Ground) are the GPS-reported equivalents of what yacht-navigation courses call "effective course" (rumbo efectivo) and "effective speed" (velocidad efectiva) — the vessel's actual direction and speed relative to the seabed after accounting for leeway and current.▶ 0:07 The explanation builds from first principles using vector diagrams. True heading and boat speed (Vb, read from the log) form the first vector.▶ 0:57 Leeway — zero when running downwind, up to 10 degrees on a close-hauled course — rotates that vector to produce the surface course.▶ 2:11 Adding the current vector (direction and magnitude) produces the final resultant: the effective course and effective speed.▶ 3:06 When current opposes the boat, effective speed falls below Vb; when it has a favorable component, effective speed exceeds Vb.▶ 3:59 GPS chartplotters calculate and display COG and SOG directly from satellite position fixes, bypassing the log and compass entirely.▶ 4:56 Confusing GPS-derived COG/SOG with compass heading or log speed is a common error the tutorial explicitly addresses.
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