Here are my top ten tips for sail trim in no particular order:
• Helm - The helm should feel balanced and comfortable to hold in your fingertips. A few degrees of weather helm is desirable for a margin of safety. The key is to maintain this balanced helm through varying conditions with sail trim and angle of attack.
• Heel Angle - Depending on your boat and conditions one should sail the boat as flat as possible with no more than a comfortable angle of heel of 10-15 degrees in a breeze.
• Angle of Attack - When sailing close hauled with the boat powered up, the boom should be at or close to the centerline of the boat for maximum sail power. The angle of attack for each sail is measured from the chord line to the apparent wind direction. The same angle should be maintained as you head off the wind and ease sail. Note that the main will generally have a slightly higher (smaller) angle of attack than the jib. When bearing off more than 90 degrees (beam) the angle of attack will gradually increase.
• Attached Airflow - Monitor telltales to insure they are streaming aft, indications of attached airflow. Jib telltales should be located 12" aft of the luff and flowing on both windward and leeward side. Main telltales at the leech end of the top two battens should be flowing aft at least 2/3 of the time.
• Jib cars - Preset the jib cars evenly on port and starboard to their base settings and adjust as necessary once you determine the luff "break". The luff should backwind evenly from top to bottom when you luff up - the top may break slightly ahead of the bottom. It the top breaks too early cars forward and if the bottom breaks early cars back ("bottom back").
• Sail Twist - Monitor the leech of the main (for sail twist) by generally keeping the top batten parallel to the boom unless you are beginning to stall or conversely becoming overpowered when you would ease to open the leech.
• The Slot - Match the leech profile (sail twist) of the headsail to the mainsail. Don't close off the slot or cause excessive backwinding (downwash) which may be seen on the mainsail luff. Maintain an even slot profile between sails and insure the jib leech does not hook in or out.
• Sail Shape - Scan the camber (curvature) of the sail fore-n-aft along the draft stripes or seams noting the depth and point of maximum draft. Typically you will have a rounded entry at the luff and flat exit at the leech and as the wind increases depth should be reduced and the draft position moved forward.
• Shifting Gears – Keep your boat at maximum efficiency by trimming to the proper gear as you would with a stick shift automobile. Use use sail shape and angle of attack to "upshift" (trim) as you power, or "downshift" (ease) as you slow down when wind and sea conditions change.
• When in Doubt - "Let it out". An old adage that has proven the test of time. Do not overtrim!
By Brian Jones