Main Trim

These are some basic factors in Main Trim.

Factors in trimming:

  1. Main moves back and forth (up and down) -- traveller controls
  2. Main twists off -- sheet controls
  3. Draft measured in depth -- backstay, outhaul controls
  4. Draft measured fore and aft -- cunningham helps control

Trim in this order:

  1. Set twist: Pull sheet in all the way and/or until top batten in parallel with boom
  2. Set draft depth: Backstay on, outhaul on to flatten sail (deeper for light air, flatter for medium to heavy, flat or "bladed" for heavy.)
  3. Set draft forward: Use cunningham, a little for light air, more for medium and major for heavy air
  4. Set boom: traveller should be just to windward of centerline with boom on centerline. Ease in puffs and/or heavy air or to reduce weather helm.

Controls:

*Backstay: flattens sail when on; should be on for upwind, off for running; loosens leech when on.

*Sheet: controls twist in top of sail; should be on all the way for upwind; letting out depowers sail by twisting off the top; this should not be the first way of depowering for puffs.

*Traveller: controls angle of the boom; boom should be centerline for upwind with top batten parallel to boat's centerline; traveller should move down for puffs; number one way to depower sail; for heavier air and to depower, let traveller down; for running or reaching adjust traveller accordingly to give boom furthest angle out.

*Vang: helps flatten bottom of sail by pulling boom down but will not help much here -- use sheet instead; should be on for downwind as it powers the sail up by making more sail area and keeping the leech solid. First way to depower for downwind on most larger boats. Controls twist downwind because mainsheet is no longer pulling down. Keep upper batten parallel to boom.

*Outhaul: pulls foot of sail tight across boom; should be fairly tight for upwind to help flatten bottom of sail; should be looser for downwind so main isn't overstrapped. If the waves are big for the wind, east outhaul slightly for more power.

*Cunningham: pulls luff of main tighter; used to move draft fore and aft; more cunningham moves draft further forward.

Closehauled Settings:

These will vary slightly due to sail itself.

  1. Sheet all the way in. (For heavy air, it may be adjusted, although too much twist creates drag and is slow.) Trim with top batten parallel with centerline. Note: For a masthead rig, sometimes top batten can be overtrimmed to poke to windward for smooth water and medium air due to full hoist jib. Will help pointing. Sometimes, a little twist off the top can also help in chop and light air to prevent stalling.
  2. Backstay on to flatten sail to draft appropriate for wind strength. For light air, deeper draft. Medium air, shallower. For heavy air, sail should be fairly flat. For heavier air, battens should be straight across with very little draft. Too correct overbend wrinkles, use windward checkstay or runner.
  3. Outhaul should be on enough to tighten foot across boom. For heavier air, outhaul should flatten bottom third of sail. (Ex. 2 inches from band at end of boom for light air, all the way on for medium and heavy.)
  4. Draft should be 33-50 percent forward. Use cunningham to pull it forward if necessary and take any wrinkles out of the luff. (There may be band at the top for the halyard position.)
  5. Traveller probably slightly above centerline to bring boom to centerline.

Running:

General Notes:

Draft should be further forward and deep in really light air.

Traveller can be continually trimmed. Talk to the driver about helm and watch speed.

Don't overvang in light air. Common mistake. If someone is holding boom out, have them push it out but not down.

Common problems/How to fix

Leech too "tight": Open up by more mast bend. More outhaul opens lower leech. Then adjust cunningham and sheet. (Backstay tension moves draft aft.)

-Main too flat: Backstay off, outhaul off until draft appears then adjust with cunningham, and sheet if necessary.

-Back of main (where battens are) not flat and/or straight: "Blade it out but adding backstay tension and outhaul if necessary. Adjust cunningham, and sheet if necessary.

-Main is hooked laterally to one side: No twist. Sheet out until batten comes parallel to centerline.

-Too much draft: Add backstay to flatten, then trim sheet for twist and add cunningham to bring draft forward.

-Too much weather helm: Traveller down. Backstay (to flatten top two thirds). More outhaul (or flattener) to flatten bottom third.

How to trim an old main:

Old mains usually have tighter leeches, draft to far back and too full.