ASA ASA Sail Trim & Performance 2 — Questions and Answers
Question 1: What is 'twist' in a sail, and why is some twist desirable?
- The leech falling off to leeward at the top, matching the wind gradient aloft (Correct answer)
- The foot curving outward
- The luff hooked to windward
- Wrinkles running diagonally across the sail
Correct answer: The leech falling off to leeward at the top, matching the wind gradient aloft
Sail twist allows the upper part of the sail to feather slightly, compensating for the wind's natural shift in direction with altitude (wind gradient).
Question 2: What does a wrinkle running from the clew toward the luff indicate about jib trim?
- The sheet is eased too much and the sail is under-trimmed (Correct answer)
- The halyard tension is too high
- The lead is too far aft
- The sail is over-trimmed
Correct answer: The sheet is eased too much and the sail is under-trimmed
A horizontal wrinkle from the clew toward the luff indicates the sheet is too loose and the sail's foot is not under proper tension, requiring the sheet to be trimmed in.
Question 3: Which sail control primarily affects the mainsail's leech tension?
- The mainsheet (Correct answer)
- The cunningham
- The outhaul
- The traveler
Correct answer: The mainsheet
The mainsheet is the primary leech tension control on the mainsail; pulling it in tightens the leech and reduces twist, while easing it opens the leech.
Question 4: When does headsail 'backwinding' the mainsail become a problem?
- When sailing close-hauled and the jib is trimmed too far inboard (Correct answer)
- When running downwind with the jib poled out
- When reefing in heavy air
- When tacking in light air
Correct answer: When sailing close-hauled and the jib is trimmed too far inboard
If the jib is sheeted too far inboard when sailing upwind, the air exiting the slot deflects into the mainsail's leeward face, causing it to collapse or backwind.
Question 5: What does moving the jib lead aft accomplish in terms of sail trim?
- Opens the leech and flattens the upper part of the sail (Correct answer)
- Closes the leech and powers up the sail
- Increases forestay tension
- Moves the draft aft
Correct answer: Opens the leech and flattens the upper part of the sail
Moving the jib lead aft increases tension on the foot and eases the leech, opening the top of the sail and reducing power — useful in stronger winds.
Question 6: What is the primary advantage of a fractional rig over a masthead rig for sail trim?
- More control over forestay sag and mast bend through backstay adjustment (Correct answer)
- Larger sail area overall
- Simpler running rigging
- Better performance in light air without adjustments
Correct answer: More control over forestay sag and mast bend through backstay adjustment
A fractional rig allows the backstay to directly bend the mast and control forestay sag, giving the skipper powerful tools to flatten the mainsail and adjust jib luff shape.
ASA ASA Sail Trim & Performance 2
What is 'twist' in a sail, and why is some twist desirable?