Tuning Guide
 

Dear J/24 sailors,

Thank you for your interest in our sails. For over a decade we have been developing our J/24 sails to achieve better speed to help you win on the race course. With fast changing technology and more sophisticated tools available it is a very exciting process which never ends. At Z Sails we are constantly working to refine our designs to achieve superior speed. Winning races doesn't rely on the speed alone. You need good crew work, good tactics, good strategy and maybe some luck from time to time. But boat speed always helps. This tuning guide provides the information you need to get maximum speed with your Z Sails.

BOAT PREPARATION

As you know the J/24 is a very unique boat. It lacks weather helm in light air, so in order to get your boat to it's potential speed you have to spend some time to prepare it. The boat preparation process is aimed at reducing drag and increasing the weather helm to help improve your J's performance.

Bottom
The class rules allow you to fill the imperfections (hollows) in the hull but not remove gel coat in order to achieve a fair surface. When this is done, we advise painting the bottom with hard Epoxy and wet sanding it with 600 grit sandpaper. On our boat we wet sand the bottom before every major regatta.

Keel
Optimum performance of the J/24 requires that your keel will be:

-maximum forward
-maximum chord
-maximum depth
-minimum thickness

Moving the keel forward is achieved by removing material from the trailing edge and building up the leading edge. Next, you need templates to fair it to minimum thickness. It can be a long tedious process if you do it yourself, so if the budget allows we would advise you to give it to professionals.

Rudder
The rudder shall also be:

-minimum thickness
-minimum weight (total with tiller and hiking stick = 13.5 kg)
-mounted at minimum depth as per class rules Plan D.

You need class templates to achieve this. Then wet sand with 600 grit sandpaper.

Rig
As we mentioned before the goal is to increase weather helm in light air. This is achieved by moving the sail plan as far aft as possible. Therefore you will need to:

-shorten your mast to class minimum
-set headstay length at class maximum
-cut your spreaders to class minimum
-adjust spreader sweep-back to around 155 mm.
-set your mast with maximum allowable J of 2910 mm.

After all this is done you are ready for a next step - rig tuning.

RIG TUNING

Make sure that your mast is centered and in column in the boat. To do this we place marks on starboard and port side at the toe rail equal distance from the bow. Using the Genoa halyard we hoist a steel measuring tape and check the distances on both sides of the boat. By tensioning the upper shrouds with the lowers slack center the top of the mast. Next adjust the mast at the partners sliding one way or another, side to side to keep it in column. Last thing to do is tighten the lowers constantly checking the straightness of the mast.

We use a Loos Tension Gauge, Model B to set the shroud tension. Start with 25 on the uppers and 20 on the lowers. At this tension, there should be about 1.5" of prebend. The best way to measure this is to attached your main halyard to the gooseneck, tension it and get up on the mast with a ruler and measure between the back of the mast and the halyard at about spreader height. For readings less than ideal (say, 1") move the step of the mast back. For readings more than required (say, 2") move the step of the mast forward. Occasionally we will use a smaller prebend (1"-1.25") if we are facing heavy air regatta. It can be a time consuming process, but you do this only once. When you get it right the headstay tension should read about -10 with the backstay slack (wire blocks about 10" below the bridle).

Now the shroud tensions vary in different winds as follows:

Wind Uppers Lowers
Very Light ( 0-4 kn. ) 15 9
Light ( 4-8 kn. ) 20 15
Medium Light ( 8-12 kn. ) 25 20
Average (3 on rail) ( 10-14 kn. ) 27 25
Medium Heavy ( 12-16 kn. ) 29 28
Strong ( 16-20 kn. ) 31 31
Very Strong ( 20 and up ) 32 33

SAIL TRIM

The next thing is the trim of the sails. This is the most difficult part since it is so complex and involves developing a feeling of the boat performance. Briefly, you always have to pay attention to the interaction between the main and genoa which is indicated by the backwind on the main.

Genoa
This sail has to cover a very wide range of wind - 0 to 18 kn. Therefore all adjustments are critical to maximize its performance.

Halyard tension: For light air we set up it loosely, so we can see pretty big scallops (about 0.75") between the hanks of the genoa. This will ensure the draft stays back which helps pointing. When the breeze increases we gradually tension the halyard to just get rid of the wrinkles at about 12 kn. true. Use cunningham to fine-tune the draft position during the race.

Lead: Set up your genoa lead so when you trim it touches the shrouds at the chainplate and the spreader at the same time. This is what we call baseline position. From it the genoa lead goes forward for the light air( with ease on the sheet) and back for heavier wind when you want to de-power. If you trim your genoa and the backwind on the main extends back about 2-3' it is too much. This will mean that you have to trim the main more to separate it from the genoa or ease the genoa more on the sheet. We would suggest the following settings of the genoa:

light medium heavy
Genoa Foot from chainplate 6-8" 1-2" 6-10"
Genoa Leach from spreader tip 6-8" 1-2" 8-12"

At all the time we look at the backwind and the heel of the boat. This will tell you exactly if you have to retrim. We would allow 0-10 degrees heel and a trace of backwind on the main.

Main
Halyard: For light air tension the main halyard so you can see small horizontal wrinkles in the luff. This will help to keep the draft in the back of the sail. We like to position the maximum draft at 45-50%. As the breeze increases start tensioning the halyard to smooth out the luff wrinkles. In heavy air re-tension the halyard before the race and use the cunningham to keep the draft forward.

Traveler: In light air position the traveler to windward and center the boom with the main sheet, to keep the top batten parallel to the boom. When the breeze increases move the traveler to the middle and tension the main sheet so the top batten is hooked to windward 5-7 degrees, stalling the top telltale about 50% of the time. This helps pointing and works best in flat water. In chop keep the top batten parallel or even slightly twisted (opened).

When everybody is hiking and the breeze builds you have to start to de-power. We do this by dropping the traveler down and tensioning the backstay. Remember that the backstay affects the leech tension of the mainsail, so every time you tension the backstay trim the main harder to prevent over twisting (opening). We like about 5 degrees of twist in twisted mode. When your backstay is max and you are still overpowered switch from traveler sheeting to vang sheeting. Tension the vang to keep the top batten twisted off ~ 5 degrees and play the main sheet in the puffs. When the puff hits and the main flogs, ease the genoa sheet 2-3" to stop flogging.

Outhaul: The outhaul adjustment is simple: upwind, ease the clew 2" from the black band for light air and chop, 1" for medium and right to the band in anything else. Downwind we ease the main about 2" from black band.

Jib
Trim of the jib is rather simple. The halyard is always tensioned so there are no scallops between the hanks. In order to achieve maximum tension, sail down wind, ease the backstay and then pull on the halyard. The lead position is with the center of the block even with the shrouds and only for very strong breeze we move it back ~1.5". To achieve maximum speed from your boat the jib sheets must be played constantly - eased in puffs and trimmed in lulls. We trim so the upper leech is 2-4" outside the spreader tip in a puff and 2-4" inside the spreader tip in a lull.

Spinnaker
We put our spinnaker pole on the lower mast ring most of the time. Set the height so the pole is about parallel to the water. The curl in the sail should appear in the middle of the luff. If the spinnaker breaks higher - raise the pole, if the break is lower - lower the pole. A good general rule is to keep pole perpendicular to the apparent wind. For a better down wind angle and maximum projected area try to square pole back as much as possible.

Downwind - light air: keep the boat moving all the time. Do not try to go to low. This will take the pressure away from the spinnaker and the speed will drop. It takes a lot of time to rebuild the speed. Good communication between the trimmer and the helmsman is absolutely essential. When it's choppy do not move spinnaker pole too far back, since it flattens the sail.

Downwind - medium and heavy air: set the pole so the luff of the spinnaker rises up vertically from the pole end. Ease the sheet in the puffs to help the boat accelerate and retrim in the lulls. The clew of the sail should fly slightly higher than the tack. For survival conditions lower the pole and tension the tweaker to stabilize the spinnaker.

SUMMARY

Every crew have a different style of sailing which works for them. This tuning guide is meant to enhance your sailing techniques and be a "how to" guide to achieve maximum speed from your boat. Do not try to memorize it - try to understand it! Only then you will be able to retune and retrim your boat to constantly changing conditions.

Have fun racing your J/24 and we'll see you on the race course.

Sincerely,

Chris & Waldek Zaleski
"Twins" USA 5259