YachtCaptain is a visual sail trim trainer for your wrist. Drag the wind arrow with your finger, or use buttons, and see in real time: • Where the true wind comes from (red arrow) and where the boat actually feels it (blue arrow — apparent wind) • The current point of sail: Close-hauled, Beam reach, Broad reach, Running • Correct boom angle for the main sail • Correct jib angle (automatic wing-on-wing on dead downwind) • Sail draft (camber) that adapts to wind strength and angle Adjust true wind speed and boat speed to match your conditions — apparent wind angle, sail trim and camber update instantly. Perfect for: • Sailing students learning points of sail and basic trim • Skippers reviewing wind theory before a trip • Sailors curious about why their boom should go further out at broad reach Controls: • Tap or drag — set wind direction • ENTER — switch between editing wind speed, boat speed, or wind angle • UP / DOWN — change selected value No GPS, no sensors, fully offline. Just sailing physics on your wrist.

═══════════════════════════════════════ FORMULAS USED ═══════════════════════════════════════ APPARENT WIND ANGLE (AWA) The wind you actually feel on a moving boat: awX = TWS · cos(TWA) + boatSpeed awY = TWS · sin(TWA) AWA = atan2(awY, awX) AWS = sqrt(awX² + awY²) TWA, TWS = true wind angle and speed relative to land. boatSpeed = boat speed over water. POINT OF SAIL (based on TWA) |TWA| under 40° — No Go zone (irons) |TWA| 40 to 55° — Close-hauled |TWA| 55 to 80° — Close reach |TWA| 80 to 110° — Beam reach |TWA| 110 to 150° — Broad reach |TWA| 150 to 180° — Running BOOM ANGLE (relative to centerline, by AWA) |AWA| under 20° — 0° (sail luffs) |AWA| 130° or more — 90° (boom fully out) otherwise — (|AWA| − 20) × 90 / 110 Sign = side of AWA; the boom always swings to the leeward side. JIB ANGLE jibAngle = boomAngle × 0.85 (jib trims tighter than the main, since it works in cleaner air upstream of the mast) SAIL DRAFT (camber) — depth of belly camber = clamp((|AWA| − 20) / 160, 0..1) windFactor = if TWS under 5 knots — TWS / 5 if TWS over 20 knots — 1 − (TWS − 20) × 0.02 otherwise — 1.0 clamped to range 0.3 to 1.1 mainDraft = halfLength × (0.03 + 0.16 × camber) × windFactor jibDraft = halfLength × (0.025 + 0.12 × camber) × windFactor Result: flat sail close-hauled or in heavy wind, full belly on broad reach. WING-ON-WING (automatic) if |TWA| is 155° or more — jib flips to the windward side (prevents the jib from being blanketed by the main on dead downwind) NOTES • Point of sail is defined by TRUE wind (TWA) — what the wind looks like from land. • Sail trim is calculated by APPARENT wind (AWA) — what the sail actually feels. • AWA is always closer to the bow than TWA when the boat moves forward.