Which control line can influence both depth of sail curvature and twist?

• A. Outhaul
• B. Backstay
• C. Mainsheet
• D. Vang

Answer: (B)

Backstay tension is the lever that changes how the mast sits and bends. When you tighten the backstay, you bend the mast backward, which reshapes the mainsail. This mast bend flattens the sail, reducing the depth of curvature (draft), and it also alters how the draft is distributed along the height, which changes the twist at the head of the sail. Conversely, easing the backstay allows more bend, deepening the draft and increasing twist. Other lines mainly affect one aspect—foot depth with the outhaul, boom angle and general twist with the mainsheet, or head-area twist with the vang—whereas the backstay uniquely links mast bend to both depth and twist.