Tuning guide

Upwind Mainsail Trim

These are basic tips for trimming the J 80 main which will help you establish a go-fast position for your own preferences in trim.

TWIST IS FAST. By twist, we mean that it is necessary to open up the top of the leech and maintain flow over the top of the sail. A good rule of thumb is to trim until the top leech telltale is just stalling and then ease out 2-3″ inches of sheet so that the telltale is flowing again. This is unlike many other one-designs that like to have the top batten parallel to the boom in most conditions. In order to keep the sail powered up and the boat pointing with so much twist, it is necessary to pull the traveler farther to windward than you may expect. Quite often, the boom is 15-20″ above centerline.

As the breeze builds, you need to maintain a balanced helm. Begin by pulling on the backstay to flatten the top of the main. Drop the traveler down in increments of 6″ for every 3 knots of breeze above 10 knots. As you drop the traveler, you need to pull more mainsheet to tighten the leech and maintain pointing ability. In a big breeze, the top of the main is twisted off and the bottom 1/3 of the main is doing most of the work.

Jib Sheet

The jib shape is achieved by three controls; jib sheet tension, jib car placement and jib halyard control. The sheet tension has the most obvious effect. The jib sheet controls the leech twist and how far the sail is pulled in. If you look at the overall sail as it relates to the sheet, it does two things. Picture the boat on a close-hauled course with the jib luffing as you pull in the sheet. First, the angle of the sail changes, then as the last few inches are tensioned the leech gets tighter. In short, it pulls it in and then it pulls it down.

It is important to try to match the leech profile of the jib to the profile of the lee side of the main. Try to envision how the sails would look from a motorboat trailing behind you.

The jib car controls how flat or round the jib is in the lower section of the sail and the amount of leech tension in the jib. The farther aft the car is on the track, the flatter the bottom third of the sail is and the less leech tension you have. Conversely, the farther forward the car the more round the foot and the tighter the leech. When the lead is at its maximum desired aft position, the foot of the jib will crease as the middle batten comes parallel with the centerline of the boat. In short, a rounder shape delivers more power, a flatter shape delivers more speed. In flat water, you want a flat sail. In bumpy water you want a full or rounder sail.

The jib halyard tension subtly changes the draft characteristics of the sail. As the halyard is pulled tighter, the draft of the jib moves forward and as the halyard is eased the draft moves aft. In lighter air, the halyard tension should be loose enough so that there is a hint of wrinkling in the luff of the sail. As the breeze builds, the halyard must be pulled on harder to eliminate those wrinkles, but not so much that you over stretch the material.

Crew Position

When sailing upwind in most conditions, the skipper should be straddling the traveler bar. In lighter breeze, move up in front of the traveler. The crew should hike out in between the two aft stanchions. In light air, the forward crew should move forward, even with the cabin top.

Downwind Mainsail Trim

Be sure to power-up the mainsail when sailing downwind. Ease off the cunningham, outhaul and backstay. Adjust the vang so the top batten is parallel to the boom or just slightly open. Be sure not to hook the battens to windward with a lot of vang tension.

Spinnaker Setup

When setting up the spinnaker gear, be sure that the tack line goes over the lazy sheet (the sheet going to the opposite side of the boat). This ensures that the spinnaker will jibe to the inside, between the headstay and the luff of the spinnaker, as opposed to around the outside of the luff of the spinnaker and in front of the boat.

Spinnaker Trim

Like all spinnakers, the spinnaker sheet should be eased until the luff carries a slight curl. The real trick to flying the sail and having the best downwind performance, is to maintain constant dialogue between the skipper and trimmer. Together, they keep pressure in the sail without sailing too high and loosing VMG (velocity made good to the mark). As a general rule, the boat sails downwind at 135 degrees to the true wind, jibing through 90 degrees. As the breeze builds, it is possible to sail deeper angles while maintaining good speed. One trick to get down the course fast in a strong breeze is to sail nearly dead downwind with the tack line eased out 12-18″. Heel the boat to windward and ease the sheet out. This rotates the chute out from behind the main’s windshadow, exposing maximum sail area to clear air. Experiment with this a bit and you will quickly get the feel for how low you can go without stalling the chute behind the main.


Occasionally, there are tactical advantages to pulling the wing-and-wing trick out of the bag. In breezes of over 13-15 knots, it is possible to bear off to dead downwind, heel the boat to windward and flip the main to the other side. The trick to making this work is heeling the boat to windward and keeping it from rocking and rolling. As soon as the spinnaker starts to look unstable and might collapse, quickly flip the main back over and head up onto a normal jibing angle. When things settle down, flip back to the wing-on-wing, and get going downwind again. The time to use this is when you are looking to make the leeward mark and can gain by not throwing in two jibes.

It is important that you recognize that wing-in-wing is less stable than sailing jibing angles. It can not be used when the boat is rocking and rolling. If you get the crew to move their weight around to keep the boat from rolling to leeward, the time spent on the wing can be longer. Practice this and let us know what you think. It will definitely get some wows back at the yacht club bar.
Tuning the Rig

Before Stepping the Mast Headstay Length. The headstay length is measured from the center of the pins at the hounds to the stem fitting and should equal 32′ 9 1/2″. The standard headstay is often too shor

Backstay Length. 

By lengthening your headstay, your backstay may become too long. Have your local rigger shorten your backstay wire that runs from above the backstay bridle to the mast crane so it measures 28′ 6¾”. Each backstay leg should measure 8′ 9 3/8″.

After Stepping the Mast

Mast Butt Placement. The base of the mast should be positioned 8. 1/2-9″ forward of the main bulkhead. Measure from the back surface of the mast to the leading surface of the bulkhead. The placement is correct when the headstay is taught and the mast is touching the aft edge of the mast collar at the deck level. Once the mast butt is in position, tighten it down to secure it.

Mast Blocks

The mast blocks secure the mast in the partners (collar) at the deck level and should be carved to match the curve of the mast in the front and the back. The side of the mast should be secured with rubber inserts cut from the original mast shim. The purpose of the mast blocks is to wedge the mast in place and keep it from moving side-to-side.

Fine Tuning the Rig

  1. With slack lowers and slack intermediates, tighten the upper shrouds hand tight so that they are both snug while keeping the mainsail track straight when you sight up it from the gooseneck. Cleat the main halyard so the shackle touches the rail at the chainplates on one side using a light pull. Measure the same spot on the other side of the boat. If the mast is in column, the shackle will touch in the same place. If not, adjust the uppers until it touches in the same place.
  2. Now that the mast is in column, pull on the backstay as hard as you can. This should bend the rig and loosen the upper shrouds. Now tighten the uppers again so the new slack is taken out. Be sure to tighten the same number of turns on either side. Now you may loosen the backstay. The result will be approximately 780 lbs. of tension or 32 on the Loos Gauge.
  3. Again, sighting up the mainsail track to keep the rig straight, tighten the lower shrouds, with equal turns on either side, to 22 on the Loos Gauge. Given this tension, the result should be I.5″ of prebend. Now tighten the intermediate shrouds with equal turns on either side to get a tension of 18 on the Loos Gauge. Check the rig for overall straightness, both at the dock and again while sailing, by sighting up the mainsail track. Adjust the shrouds appropriately to get the mast straight.

On the Water in Changing Breezes

Your mast tuning is now complete for 8-15 knots. When sailing in less breeze, you should take off about three full turns on the lower shrouds and take out the forward mast block. This will increase the prebend in the mast, give you a softer headstay, and give you the optimum sail shape for light air. See our Tuning Matrix at the end of this guide for detailed shroud tension instructions.

t, so you may need to add toggles to the bottom of the headstay under the roller furling fittings.

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You should go over certain areas of your J 80 whether it is used or brand new and out-of-the-box to ensure your boat is race ready. Many of these tips are applicable to the preparation you would do for any one-design racing boat.


A clean, fair underbody is essential for fast racing finishes. Be sure that the bottom is smooth and free of any bumps or hollows. If your boat is not dry-sailed, a very hard bottom paint is recommended for racing. There are several racing bottom paints available that have good anti-fouling properties. Occasionally, go over the bottom with 600 grit wet sand paper to maintain the smoothest finish. Contact your local boat yard, ship chandlery or Shore Sails loft to find out about the latest paints.

Keel and Rudder

Wet sand your keel and rudder to a smooth, fair finish.


Remove the spinnaker halyard cleat from the mast. Attach a turning block to the padeye on the starboard side of the mast base to lead the spinnaker halyard to the cockpit. We have found this works well for hoisting the spinnaker, keeps the forward crew in the cockpit to help gather the spinnaker and makes shorthanded sailing much easier