Thistle Tuning Guide - Northwest Design

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ON THE WATER QUICK GUIDE (Northwest design): Click here to download

Updated Jan 2007

To get the best results with your NORTH “NORTHWEST DESIGN” Thistle sails you need to learn to trim your sails correctly. Since the cloth in these designs is quite firm, adjustments don’t need to be as drastic as with sails made of a softer cloth. A small adjustment affects the entire sail. Once you have sailed with the sails a bit, you will learn what if feels like when they are adjusted properly and you will be able to make minor adjustments to maintain good speed as the wind and sea conditions change. If you have any questions, please give us a call.

BEFORE SAILING

The LOOS TENSION GAUGE
The Loos tension gauge is a relatively accurate instrument that will help measure the tension of your standing rigging. The newer Loos Pro gauge is spring loaded and some sailors have found it to be slightly more accurate and reliable than the Loos Model A. Following is a comparison of the numbers between the Model A and the Pro gauges. We have broken down the numbers for both 1/8” forestay tension and 1/16” diamond tension.

1/8” Cable Forestay Tension

1/16” Wire Diamond Tension - With North Northwest model sails

Diamond Stay Tension
We use the Loos Tension model A gauge (old style gauge) factors when discussing wire tensions. Individual gauges vary by as much up to 6 factors. Reading can also vary slightly due to heating (possibly uneven) of the mast. Just remember what works is more important than what the numbers read. For ABO, Ballenger, Wilson and Cobra masts the Loos gauge diamond tension should be between 12-14 (Loos factor). For Bryant or Great Midwest you should have about 3 factors more tension (15-17). These are starting tensions. Read the next paragraph and use it to analyze and refine your tune.

Correct diamond stay tension is the key to good speed in 12 knots and over. In this much wind the sail must start flattening and easing the leech off in the puffs especially in the area of the upper batten. Correct tension requires a bit of trial and error. Most people tend to have them too tight rather than too loose. Diamond tension should get progressively looser (lighter) as you move up the mast. The effect of diamonds that are too tight is that the boat heels over and rounds up in the puffs instead of accelerating forward. When the diamonds are the correct tension, the mast bends in the puffs and the main flattens out but does not luff. If the diamonds are too loose you’ll have trouble pointing. The sail will get large inversion wrinkles across the middle due to the excess mast bend. For lightweight crews (less than 430 lb.) set the diamonds at 6-8-10, as a starting point to allow the top of the mast to bend and depower. For normal crew weights of 450 lb. and up a good tension range is as follows:

Remember to tune your diamonds by supporting your mast at each end beyond the diamond attachment point, with the sail track up. Sight down the sail track to see if the mast is straight, tighten or loosen individual diamond nuts to straighten the mast. Once straightened, make even turns on the nuts at each respective height while tightening or loosening the diamonds. Tuning for a straight mast means the tension on the port & starboard diamonds at each respective height may be 1-3 Loos numbers different.

Mast Butt
Set to minimum “J” dimension of 4’9” (from forestay to front of mast). Pay attention to the gap at the forward edge between the mast step and the mast butt. The larger this gap is the more the mast will bend.

Rig Tension/Prebend
Maintain sufficient tension to keep the leeward shroud from going slack when the crew starts to hike. Tighter is better. However, if you have an old boat, be careful not to over-tighten the forestay. It is not necessary to break the hull in order to be fast. As noted on the chart above, the forestay should end up in the range of 21-32 factors.

Make sure the mast is not reverse bending when the rig is tensioned. It should at least be straight before putting the main on. If the mast reverse bends, the main will set too full for light air. If this is the case, put some spacers under the aft edge of the mast step cast (between the casting and the grating). More pressure at the back edge of the mast will push the middle of the mast forward when the rig tension is applied decreasing the reverse bend and encouraging positive bend.

Mast Rake
27’ 0” measured to the bottom (aft side) of the tiller opening with the main halyard shackle pulled up hard against the sheave. Rake measurements vary with different boats due to variations in hull shape. One-inch rake changes will effect pointing ability and helm feel.

Jib Leads
17-1/2” off centerline and 108” aft of the headstay intersection with the deck. In heavy air and especially large choppy seas (or when it becomes difficult to keep the boat flat) move the leads out 1-2”. This is the key ingredient in keeping the slot open when the traveler is being dropped to leeward. It will also help you keep the boat flat and moving at the same time.

Mainsail - Put the bottom of your luff rope in the lower mast groove. This is important to the shape of the foot.

WHEN SAILING

Mainsheet
2” or 3” adjustments in mainsheet tension is in conjunction with wind velocity changes will bring improvements in overall speed and performance. In light air, trim so that the top batten is parallel to the boom and the leech telltale at the top batten is beginning to stall and wrap around the leeward side, about half of the time.

In medium wind of around 10 or 12 knots - when just full hiking and the boat is up to speed, the hardest mainsheet tension can be used particularly in flat water. These are your optimal pointing conditions. At this time you will be within 5” or 8” of being two-blocked (we are never two blocked). NEVER PULL IN THE SAIL THIS TIGHT OUT OF A TACK OR MANEUVER, ONLY WHEN THE BOAT IS UP TO SPEED! In either heavier or lighter air (more critical conditions) the main can be 10” - 12” from two-blocked. If the wind is extremely light you can let out more if you need to. As long as you can keep the boat flat, keep the top batten parallel to the boom for good pointing ability. In heavy air the sheet has to be eased slightly to balance the boat. It’s easy to over trim the sheet in heavy air.

When reaching, the sheet should be as far out as possible without the sail luffing. If you have a hard time seeing when the sail is luffing try adding a set of telltales 2’ aft of the luff at about 1/2 height of the sail as a guide. Over trimmed is better than under trimmed. In heavy air, work the mainsheet until your arm falls off to keep the boat flat and planing.

Centerboard
When sailing to weather, the centerboard rollers should be pulled aft (rotating the board forward) as soon as the wind is strong enough to have all three on the high side. Once you’re starting to depower regularly the rollers should be rolled forward to the back of the hump. When reaching pull the board up half way so the boat can slip sideways slightly instead of being forced to heel. Pull the board up more as soon as you start planing. The forward crew can play the board from the rail. You need to stay in the groove between excessive heeling and slipping sideways.

Vang
The vang controls the leech downwind the same as the mainsheet does upwind. On reaches the vang is on tight to keep the battens from falling off but over-vanging is definitely slow. Try to keep your top batten parallel to the boom when you’re not overpowered - not too tight or too loose. A good guide is to have the top batten telltale flowing or streaming aft only 25% of the time. This takes a lot of attention in changing conditions. Be sure you can ease the vang quickly when it’s blowing. If a puff hits and the boat heels, you should let the main out. If the boom hits the water, the only way to avoid swamping, or worse, is to release the vang.

When running in light to medium air - when your boom is against the shrouds - the vang should be set looser than when reaching. The top battens should be able to dump forward 2” or 3” as the boat moves on the waves. This creates a slight fanning action over the top of the sail and keeps a little flow going when running. As the wind increases use the vang to control how much twist you’re allowing. In very overpowering conditions, loosening the vang will help to stay under control. This doesn’t mean that more vang is always more power. Loosening the vang too much in heavy air, dead downwind, will start to cause rolling problems (the boat will want to “death roll” with little or no vang). Tension the vang and or pull the mainsheet in to stop the rolling.

Traveler
A free running traveler, rigged so that it can be pulled 4” to weather of centerline is an absolute must. In drifting conditions, center the traveler and ease the boom out over the quarter. In light air (2-8 knots) the traveler should be pulled to weather until the boom is on centerline. When tacking in these conditions don’t pull the traveler to windward on the new tack until the boat is moving.

As soon as there is enough wind to hike and any waves, the traveler should be constantly adjusted to keep the boat flat and pointing / driving properly. The traveler acts as a very effective rudder, which can be moved without causing drag; so don’t be afraid to use it. As the traveler is eased down the jib leads should be move outboard to keep the slot from closing excessively.

Cunningham
This is a powerful tool adjustment on the firm sailcloth main. It has some important effects. It flattens the sail as it is tensioned making the top battens fall off and pulls the draft forward. So when you pull the cunningham, the boat points lower and goes faster. The easiest mistake is to over-tension the cunningham. When this happens you point lower than you should. A little change in this adjustment has a significant affect. Don’t over tighten the cunningham. To judge this adjustment look at the amount of wrinkles coming out of the luff of the main and the draft location. A few wrinkles from a loose cunningham is better than having it too tight and, as a result, having the sail over flattened.

In light and medium conditions the cunningham should be loose enough so wrinkles come out of the luff in the lower part of the sail. This will help keep the sail to have more fullness and let the batten angle to windward to give more power. The cunningham controls the draft location so try to get used to looking where the draft is. Pulling in the cunningham moves the draft forward (when it’s trying to move back in heavier air). Having it on too hard in lighter air can move the draft too far forward (so you can’t point) and over flatten the sail. In heavy air the cunningham should be pulled down to flatten the sail and let the upper two battens fall off. For very heavy air, rig your cunningham so it get pulled down to one side of the boom, this lets you pull it on further. Always ease the cunningham downwind but don’t forget to check it before going back to weather.

Outhaul
The main has a lens foot. This allows the outhaul to directly control the angle of the lower battens and the depth in the foot of the sail. However, more important is what it does to the depth of the middle of the sail. Don’t set the outhaul too loose for light wind. The normal reaction when speed isn’t too good in light wind is to try to make the sail fuller. More often than not, the problem is that the sail is already too full.
The distance, which the top of the lens foot falls off the boom, is a good indication of how tight to set the outhaul. In light to medium air the seam at the top of the lens foot falls off the boom is a good indication of how tight to set the outhaul. In light to medium air the seam at the top of the lens should be 2 1/2” - 3 1/2” off the boom. When the boat is starting to get overpowered in the puffs close the lens foot completely or nearly so. In really heavy wind, pull it all the way, but if you do this too early you will loose pointing and power. Keep in mind your sea conditions, along with the wind speed. In flat water you should be able to tighten your outhaul considerably more than in choppier water with the same wind speed.

When reaching ease the outhaul to tighten the lower part of the leech. A little closing of the bottom two battens and having the bottom of the sail fuller helps when reaching. However if you’re over powered while reaching, don’t worry about letting off the outhaul because you don’t need the power. An important point in outhaul trim off the wind is that whatever distance might be gained in the precise setting of the outhaul downwind, is more than negated when you forget to put it back on at the leeward mark. Always make sure it goes on before the leeward mark.

Jib Trim
The jib leads should be set so that the foot of the jib fits just inside the rail (so it’s just “kissing” the rail when sheeted in) when the leech is 1” - 2” away form the end of the middle spreader as viewed through the luff window in the main. Spreader lengths vary depending on how they’re adjusted. 1 1/2” is the approximate distance for the shortest setting. The foot of the sail is trimmed so it is just barely touching the rail in moderate-heavy conditions. Move your leads out in the very heavy air or heavy choppy seas where you can’t point effectively anyway. Move them back in as soon as you can or need to or you’ll lose both pointing ability and power (see: Before Sailing, “Jib leads”).

The halyard should be pulled until the wrinkles coming away from the snaps barely go away. The luff tension can be coarsely adjusted by the lacing at the head of the sail to allow sufficient halyard tension but tight enough to take some of the load (only on your tightest setting).
In drifting conditions, the crew must hold the jib clew up and out enough to allow air to flow through the slot between the main and jib.

Steering Techniques
You’ve heard it before, and you’ll hear it again because it’s true, no one sails the boat flat enough all the time. If the droop hiking crew isn’t hitting the tops of the waves the boat is heeling too much. In a breeze the traveler has to be moved almost constantly to maintain speed and keep the mast pointing straight up, i.e., the boat very flat. This is also a function of the mast being tuned correctly by having the diamonds properly adjusted. In moderate conditions, steer so the weather telltales on the luff of the jib are lifting. Always sail the boat so that weather helm is minimal - just enough so that the boat heads up into the waves without being pushed.

With the Northwest jib we suggest sailing with both telltales streaming unless in a tight pointing situation where the windward telltale will just show a stall. Never sail with the leeward telltale stalled..ease the jib to allow the boat to accelerate.

When the wind gets light and the water choppy, the crew needs to keep moving in and out to keep the boat just flat or slightly heeled to weather in the flat spots. The boat should always be trimmed to keep pressure on the rudder at a minimum - only slight weather helm - to tell you that the rudder is helping the centerboard to lift. Always try to let the feel of the boat tell you how to trim your sails and weight. Note settings and conditions when you’re going fast. The only way you can learn how to understand your boat (and of course crew) is to get out there and sail.

If there are any questions or comments give us a call, or send us e-mail:
Jack.Christiansen@northsails.com

For tuning help contact the North Thistle experts.