The big news is the tri-radial jib that has high performance and will have a very long competitive lifetime because the low stretch directions of the cloth are well aligned to the stresses on the sail. Heavy air performance is better because the sail will stretch less under wind loading. This is particularly important because tightening the forestay is not as effective for jib flattening as mast bending is for mainsail flattening; jibs tend to get deeper right when you want them to be flatter.
The perfected sail shape of the cross-cut jib is retained by using the same broad seaming and luff curve (adjusted slightly due to the low stretch) as were used on the previous jib. The new jib is only slightly more expensive than a cross-cut jib because an innovative panel overlap method is used in place of separate corner patches. Extra labor to set up the tri-radial panels is offset by reduced labor from eliminating corner patches. For both, there are four layers of cloth at the corners. The high performance cross-cut jib is still available. Both sails are cut using a full sized mylar pattern for each panel. The sails from the big lofts come with surprising variability of shape. I have recut many of the bad ones.
All jibs are built with the same panel shaping, the leech is broadseamed for the usual fairlead positions, and the luff is cut for fairly tight forestay tension. The leech and the luff can be set differently if your boat has a different fairlead setup, or if you use lower rig tension.
The 1997 mainsail is adjusted only slightly in the leech in comparison to the 1996 design. The corner treatment is slightly improved, and the optional reefing clew reinforcement is incorporated better into the regular corner design. The reef tack now has sail slugs for the mast groove which allow excellent control of the camber of the foot. As before, the basic shape is built into all sails, but the luff curve can be cut for different masts. The standard is for the black oval mast, but the luff can also be cut for the stiff gold mast or for wooden masts.
The overall design method for these sails was to start with a proven fast shape in medium air with very little tension in the sail control lines. The outhaul leaves the shelf foot quite open so the sail has camber down to the foot. The bolt rope has low tension, so you do not need to tension the cunningham to pull out the wrinkles in the luff. You do not need vang tension except in heavy air. The sail is remarkably smooth. In overpowering conditions, the main flattens out very easily with the outhaul and vang, and the cunningham can now be used to move the camber back forward. As with more modern designs seen on bigger boats, "speed wrinkles" are a thing of the past. In retrospect, they were the sail maker's way of telling you that a fast sail might have some wrinkles because of the way it is cut. As we now understand, if wrinkles are speedy, airplane wings would have them (and we can now design sails without them).
Reefed mains are now a proven design, and almost half of the mains I make now have this option. These are very fast in overpowering conditions, and are built such that the normal sail shape is not at all compromised. They also add life to sails because they can be sailed without flogging the upper part when recovering from a puff. When reefed, the center of effort of the sail is lowered, so only a small reduction in area is necessary. The big advantage of reefed mains over twisted-off full mains is that you remove the drag as well as the excess lift from the upper part of the sail, while the flogging part of a twisted-off main still has drag. Drag is slow.
Both sails are built with Dimension/Polyant 165s htp ripstop material that most consider the best for one-design sails. It has extremely low stretch and is very durable.
Halyard tension is usually set tight enough such that the forestay just starts to sag; i.e. the wire in the jib luff is now carrying the rig tension. The cloth tension is preset at the sail loft using the lashing from the head grommet to the wire eye loop. This will not require adjustment until the sail is stretched out or abused. For this sail design, it does not ever need adjustment on the water.
Upwind the jib sheet should be adjusted initially so the mid foot is a couple of inches inside the rail, and the upper leech is just off the spreader. Then check to see if the plane of the leech in the region of the clew is parallel to the centerline of the boat (air is exiting the sail straight aft at the clew). If it is curled inward, move the fairleads aft, and vise versa if it is not curved enough. Reset the jib sheet and check the upper leech again. Meanwhile note the three sets of telltales. First there should be a trim and sailing course such that all telltales are flowing. If you then turn the boat slowly to windward, it is acceptable either that all of the telltales flutter at the same time, or that the top one flutters slightly before the others. If the top one flutters last rather than first, then the sheet tension too great, and/or the fairlead is too far forward.
Some boats have the jib fairleads moved very close to the centerline. It will then be necessary to use the barber haul to pull the sheet out slightly to get the best trim. If the sail seems otherwise quite good but the clew is hooking to windward, then use the barber hauler to pull it outward so the air exits straight aft right at the clew.
In heavy wind, it is sometimes necessary to move the fairlead forward to get
more leech tension. In heavier wind yet as you get overpowered, you can then
move the fairlead aft to twist off the top of the jib and reduce heeling.
This is usually not necessary if a reefed mainsail is used.
Main Sail Trim Upwind
This sail is constructed such that it has the correct shape for medium wind with low tension on all the control lines. Whenever you seem to not be moving as you expect or the sail shape starts to look poor, you should first loosen the control lines, and then work your way back to good trim. There is a strong tendency to pull rather than ease lines while racing, and that will not work with this sail.
Pull the halyard full up, but leave the cunningham fully eased. The luff bolt rope has low tension, and the sail should exit the mast smoothly. Any wrinkle line in the luff area parallel to the mast is to be carefully avoided as excess tension here on the bias direction of the cloth can quickly damage the sail; immediately ease the cunningham and halyard. Depending on your particular mast setup, you may need to slightly tension the cunningham to take the slack out of the luff. This is more likely if you use a halyard shackle rather than knotting the halyard directly to the headboard, as the shackle prevents full hoist.
Upwind in medium wind, adjust the outhaul so the shelf foot is just fully opened. This can be determined by pulling on the outhaul until the center of the foot just starts to move towards the boom, and then easing it slightly.
Center the traveler, and adjust the mainsheet such that the upper telltale stalls occasionally, but such that the others never stall. Normally this will occur without any vang tension, but a little vang can be used if the top of the sail seems to twist off too much to leeward.
Remember that the proper shape is built into the sail so that a correctly trimmed sail is very smooth and wrinkle free. If you start to see wrinkles in medium wind, first ease all the control lines and then work your way from there back up to speed. If you start making adjustments when the sail is overtensioned, you will probably miss the positions of correct trim.
For very light air, you can flatten the main slightly with the outhaul, ease the mainsheet until the end of the boom is at the corner of the transom, and heel the boat to leeward so the rail is only a few inches from the water.
Otherwise keep the boat as flat as possible. In heavy air when heeling is a problem, first ease the traveler. If that is not enough, flatten the sail somewhat with the outhaul. If that is still not enough, use high mainsheet tension and/or the vang to bend the mast and flatten out the rest of the sail. The sail is supplied with medium tapered battens that may not be stiff enough on windy days. Substitute untapered battens if the leech needs more support.
Various skippers play the puffs with combinations of traveler, mainsheet and vang. When the puffs are very sharp and unpredictable, then playing the mainsheet is the only way to react quickly enough. Then the vang must be used to flatten the sail. Using the traveler probably keeps the boat moving faster through less wicked puffs, but requires very good crew and skipper coordination.
When it is really blowing, or you are undercrewed, put in the reef.
Reaching Without A Spinnaker
On close reaches, trim the jib sheet to keep all telltales streaming. As the reach gets broader, trim such that the leeward telltales are at the edge of stalling, but never consistently stall. Use the barber hauler to try to minimize twist so that the telltales all break at about the same time; this is not always possible. Another way to get good trim is to use the barberhauler to try and keep the air at the clew exiting straight aft; this is only possible at some reaching angles.
Trim the mainsail such that the leech telltales are all streaming. Again, at
broader angles, they can be at the edge of stalling, but never consistently
stalling. Use the vang to remove as much twist as possible. This means that
the leech has about the same exit angle for most of its height. When trimming
in the mainsheet, it is acceptable if the top telltale stalls slightly before
the others. If it stalls after the others, use the vang to reduce twist. You
can ease the outhaul to get maximum camber, but must remember to reset it
later for the upwind legs.
Reaching With A Spinnaker
The Benson spinnaker is somewhat flatter than others such that is reaches very well, and still projects more area on runs than deeper sails. This does make it a bit more sensitive to trim, so the crew must be very attentive.
When reaching, keep the pole as far to windward as possible. This will usually be noticably further aft than possible with deeper sails where the usual guide is to set the pole perpendicular to the apparent wind direction. A good guide for this chute is to observe whether the properly trimmed luff tends to drift to windward or leeward of the pole. Trim the sheet so the luff is at the edge of folding. In heavy air, you will be fastest if a few inches fold over consistently. Adjust the guy so the luff is directly above the pole, and retrim the sheet. Set the pole height such that the tack and clew are at about the same height above the water. If you need to reach as high as possible, then the pole is at the forestay, and you can raise the pole slightly to flatten out the luff.
As much as possible, keep attached flow on the mainsail by trimming so the leech telltales are flowing, but at the edge of a stall. Refer to the reaching-without-spinnaker guide above.
Because the Thistle is quite lightweight, you can head up to gain speed , and then use the higher apparent wind speed (which also brings the apparent wind forward) to head back down to your former course while retaining the higher boat speed. Although this method seems contrary to elementary physics, it is acceptable advanced physics.
If you must sail dead downwind, then pull the pole well back, fully ease the
mainsail, and heel the boat to windward to swing the spinnaker out and away
from the mainsail. Use the vang to keep the boom from rising.
Thistle Mast Set-up for Benson Sails
Mast Step
Set mast at minimum J, 57 inches from the forestay to the front of the mast.
Mast Rake
Use maximum rake such that there is enough leech tension in heavy air with the mainsheet blocks almost touching. On most hulls, a measuring tape pulled fully up on the main halyard will measure 26 feet 11 inches to the bottom of the tiller hole in the transom. This should be checked and adjusted after sailing. Reduce the rake either if the mast two-blocks too readily, or if you have excess weather helm when the boat is sailed flat in medium to heavy air.
Diamond Tension
Use a Loos gauge. For most crew size, use around 16 on the gauge for all three. For light crews, reduce the tension up high to let the top bend off in puffs. Consider 16, 13, 10 bottom to top, or even 14, 12, 8 if you find you like the mast to do a lot of flexing in gusty conditions.
Forestay Tension
Measured at the forestay, try about 300 pounds tension (32 on the gauge for a one-eighth inch forestay). You can go slightly higher if you like to pinch in flat water, or a bit lower if you like to foot in lumpy conditions. This affects the fullness of the jib entry. Older jibs from other makers may need very high tension to flatten out the jib luff.
Mast step Shims
With the rig fully tensioned as above, the mast prebend should be very small; about half an inch measured as the gap between the middle of main halyard and the mast when the halyard is stretched down the aft side of the mast and touches only at the sheave and at the goose-neck area. If the prebend is too large, shim the forward edge of the step to put more force on the bottom front of the mast. If too small, or the mast curves the wrong way, then shim the aft edge.