Question 6 AXS01 - Auxiliary Sail Endorsement

The Correct Answer is A. ### Why Option A is Correct Option A ("When it first takes the shape of an airfoil") describes the precise moment the sail transitions from merely acting as a barrier (drag drive) to operating primarily as a wing (lift drive). * **Maximum Drive Attainment:** When the sail is flapping freely (luffing), it generates zero effective drive. As you pull the sheet, the sail fabric begins to catch the air and smooth out. The instant the sail achieves a stable, curved shape—even minimally—it begins creating a pressure differential between the windward and leeward sides, generating aerodynamic lift. * **The Transition Point:** Since the vessel is drifting broad on the port beam (meaning the wind is coming from the side), lift is the dominant and most efficient source of drive. The *maximum drive* is attained when you cease the luffing (flapping) and achieve this functional airfoil shape, as this is the point where the efficient lift drive begins to operate, providing significantly more power than the flapping sail could. Pulling the sheet further than this optimal point generally results in excessive sail angle and subsequent stalling (reducing lift and increasing drag). Therefore, the instantaneous achievement of the airfoil shape marks the beginning of efficient drive maximization. ### Why Other Options Are Incorrect **B) When it is filled with a slight flap at the leech** * This option is incorrect because the *leech* (the trailing edge) is the low-pressure side of the sail. While a small flap at the *luff* (the leading edge) is often an indicator that the sail is optimally trimmed (indicating maximum lift without stalling), a flap at the leech suggests the sail is slightly **overtrimmed** or stalled, which reduces the efficiency and overall drive force. **C) When it is 45° from the apparent wind** * Sail trim is optimized based on the boat's direction and the apparent wind angle, not a fixed measurement. While 45° might be a general rule of thumb for certain points of sail, the specific angle that produces maximum drive changes constantly with wind speed, apparent wind shift, and sea state. Trimming by feel (eliminating the flap) is always superior to trimming by a fixed angle. Furthermore, setting a sail at 45° to the apparent wind would likely cause it to stall if the wind were truly broad on the beam. **D) When it is at right angles to the true wind** * Setting a sail at 90° to the true wind (i.e., square to the wind) is only optimal when sailing directly downwind (a broad reach or run), where the drive is purely drag-based. Since the vessel is drifting with the wind "broad on the port beam" (a beam reach situation), the most efficient drive comes from **lift**, not drag. A sail set perpendicular to the true wind on a beam reach would be severely overtrimmed and stalled, providing poor drive.