Mainsail controls and adjustment

1. main sail general notes

  • Locate a tell-tale approx. 3/4 up the leech of the sail on the trailing edge (near the back of the W for the sail #)
  • Sew the battens in place to prevent loss.
  • Roll the main and jib together on large plastic or cardboard tubes to keep them smooth when not in use.  These are available from carpet stores.
  • Sew the end of a light shock cord to the leach of the main approx. 12Ē from the clew.  Fasten the other end to the end of the boom.  This cord helps to prevent spinnaker sheets from getting wrapped around the end of the boom when gybing.
  • 4 mm pre-stretch line is best for the various control lines. Use a different colour for each service to avoid confusion.


2. main halyard

  • Always hoist the head of the main up to the "black band" to keep it as high as possible.  Install a hook near the base of the mast to hold the wire halyard in place fixing the main at max. elevation.
  • Install a Velcro loop on one side of the mast support to hold the folded rope halyard.
  • Keep the boom free of the goose-neck while hoisting. then attach it.  Avoid stretching the luff of the main.  It should have tiny horizontal "speed-wrinkles"' extending out from the luff to maximize power from the main.


3. main outhaul

  • Set up the outhaul so that it is easily adjustable while sailing. Run control lines back under the thwart (or along the side of the CB housing) but preferably to each side deck for adjustment while sailing. A 3:1 or 4:1 purchase is effective.
  • In light wind, pull the clew of the main out close to the black-band to flatten the sail, this helps to maintain air flow over the sail.  A tight outhaul also helps to loosen the leach of the main. It is OK if the foot of the main folds into a shelf.  This is necessary to flatten the sail.
  • In medium air, ease the outhaul to make the sail full for max. power. Just take out the vertical wrinkles along the foot.
  • In heavy air, pull the clew out to the black band to flatten (depower) the main when going to windward.  Ease the outhaul on reaches to provide increased power for planing.


4. main sheet

  • The main sheet should be approx. 35 to 40 ft long and made from 1/4 or 5/16" braided line.
  • Fasten the mainsheet to an eyestrap at the end of the boom. Then lead it down to a block on the traveller, or bridle, back up to a block on the boom so as to provide a 2 to 1 advantage. (Alís note: Then lead it forward through a stationary eye on the bottom of the boom about 3í forward of the boom end [garrotte preventer during gybes!], and on to a block  on the boom that will be directly above your centre mainsheet swivel block when you are sheeted in.)
  • Tie a knot in the main sheet so that the boom will only touch the shroud as the knot hits the main block. This will prevent damage to the boom or shrouds when gybing in high winds. Put tape on the boom where it touches the shrouds to help prevent chafe on the wire and the boom.
  • Simple bridles are now popular in place of a traveller car. The advantage of the bridle is that the main sheet tension acts primarily to adjust the inboard/outboard angle of the boom. Downward tension on the leech of the main is minimized.  Leech tension is then left primarily to be controlled by boom vang tension. A double block arrangement is used, similar to a Laser to allow free travel along the bridle. (Alís note: These days, most people use a single block tied to the bridle. This makes it easier to keep the boom centred.)
  • Some racers switch from a bridle to a traveller for strong wind conditions. The only advantage of the traveller arrangement is that it can be let out to the corner in strong winds. This keeps the main flat while spilling air to help keep the boat level. With this set up, a strong crew can play the traveller to compensate for gusts. For this reason it is important to have the control lines lead back to the thwart where they can be easily adjusted while hiked going to windward.
  • It is critical not to oversheet the main when going to windward. Watch the tell-tale on the leach of the main and try to keep it streaming back*. If this is difficult (i.e. it tends to loop around behind the main), there may be too much boom vang tension.  If the tell-tale loops around in front of the main, there may be too little vang tension. * Alís note: Donít overdo this, however! If you want to point, the leech ticker should spend up to half of its time disappearing behind the main once your boat is up to optimum upwind speed!
  • As the wind dies, it is very important to ease the mainsheet. (When in doubt, let it out!)  In very light air, the boom must be out 1 to 2 feet, or more, to leeward of the center line of the transom.


5. boom vang (kicker)

  • Both lever vangs and block & tackle arrangements can make effective vangs. A minimum of 8:1 or 12:1 advantage is needed for good control.
  • Since the vang is the primary control of mainsail shape, it must be easily adjustable from either side of the boat while you are hiked out. Run a control line under the thwart to each side deck where it can be adjusted and cleated on the vertical edge of the side deck (Alís note: or on the aft edge of the thwart).
  • In light to medium wind, very little vang tension is needed going to windward. The prime indicator is the upper batten. The back 6 inches of it must be parallel to the boom. Too much vang will tighten the leach causing this batten to hook to windward. This chokes the air flow over the main. Too little vang will leave the leach too loose. This puts too much twist in the main making it hard to point.
  • Although it is common to go to windward with little vang tension in light to medium winds, it is necessary to apply some vang on reaches and runs to prevent the main from twisting off too much, thus spilling wind from the upper section.
  • Another indicator for proper vang tension is the luff of the main. With proper vang tension, it should luff evenly from top to bottom. It the vang is too loose, the upper section of the main will be too full. Hence it will luff first. It the vang is too tight the upper section of the main will luff after the lower part.
  • In heavy air, the vang is used to flatten the main thus depowering it so as to be able to sail the boat flat. On reaches where the power can be used for more planing speed, it is possible to ease the vang slightly.  This also helps to avoid a capsize by keeping the boom from hitting the water as easily.


6. cunningham
There is very little need for a cunningham.  It is designed to pull mainsail draft forward Ė usually when a good breeze has blown the draft aft while you are close-hauled. It takes creases out of the luff of the main when extreme mast bend has left the sail "luff- starvedĒ.  In light to medium airs, it is generally best to leave small horizontal "speed wrinkles" along the luff of the main.  Only use the cunningham upwind in heavy air to help flatten the main.