Yourbestsail · video

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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