North Sails Tuning Guide
Tuning Guide 2.4mR
North Sails Tuning guide is written to help you get the best performance from your 2.4mR.
We hope the guide will help you to more successful racing and, most of all, more enjoyable
The tuning guide is written by Björn Österberg of North Sails–Sweden and Patrik Forsgren, 1993 World Champion.
Mast Step Position
The forward bolt should be in the 4th hole from the bow.
Mast rake is best measured from the lower edge of the black band in the top of the mast to the aft end of the transom. The backstay should be pulled just enough to remove the sag. Pull the backstay hard and then release before the measurement is taken, to make sure the forestay is straight. When the mast is raked in this position, mark the position on the forestay. The mark can be made on the forestay at the bow of the boat or on the adjustment line at the cleat.
The distance is 5.50 m for all conditions.
We have tried different mast rakes. A more upright mast is hard to point well with in light and medium conditions, but gives less weather helm in heavy weather. In light winds, a more raked mast can point better but it also affects speed in a negative way.
Adjust the mast rake as described above. Mark the backstay line at the cleat when the backstay is pulled just enough to remove the sag from the headstay. Pull the backstay to the point where the mast bends 95 mm at spreader height. Put another mark on the line. Put two more marks on the rope by dividing the distance between the original marks in equal parts. Put a 5th mark with the same spacing from the 95 mm bend mark for very strong winds. The backstay tension is referred to as 1 being at the first mark, 1.5 being half way between mark 1 and 2 etc.
The shroud tension does not need adjustment for different wind speeds. With the backstay loose, the cap shrouds should be tight and the lowers significantly looser. With the backstay pulled to 4 units, the cap and lower shrouds should have equal tension.
Mast bend can be induced or restricted by the two ropes at deck level. The number we use is ½ inches (1 unit on the small North speed decal) for and aft compared with unrestricted mast position.
Place the small North speed decal just in front of the mainsheet cleat. Mark the mainsheet on a position where the mark is on the middle of the scale in about 8 knots of wind. This is to help you get back to proper trim at the start, in the beginning of a beat, or after ducking another boat. This reference is not used as reference for different sailing occasions because only a few millimeters of difference in mainsheet affects the sail shape a lot.
The mainsail tack should be fixed in a way to make sure it stays in the same position with different outhaul tension. At the same time, it is an advantage if the tack can move an inch or so along the mast. The best way to achieve this is to have a slug slide sewn to the tack of the sail. If the opening in the mast track is extended all the way down to the boom, you can't use a slide. Instead, a 5 mm rope with low friction is tied through the tack grommet and around the mast. Make sure the tack of the sail is close to the mast to prevent the clew to go beyond the black band when the outhaul is pulled tight.
The mainsail is always hoisted all the way up to the black band in the top of the mast. One way to make sure the sail is properly hoisted is to wrap woven tape a few times around the measurement band. Ease the backstay and hoist the main all the way. Pull the cunningham and tighten the halyard again.
Spreader Reference for Jib Leech
The sheeting of the jib is described as the distance between the spreader tip and the leech of the jib. The small speed decal (½ inch spacing between numbers) on the spreader helps to judge the distance. The measurements later described are valid for the standard 295 mm spreaders. If you have different length spreaders, you have to compensate for the difference.
The depth of the jib, at deck level, is described as the distance between the point where the jib hits the deck and the rail. The distance is measured 850 mm back from the forestay. A small speed decal is put at right angel to the edge of the deck with the "0" at the rail.
Sheeting Angle, Jib
The standard angle, 250 mm from the centerline, works well in all wind conditions.
The jib is always hoisted to the same point. The twist is adjusted by the barberhaulers on the jib sheet. To be able to use a mark on the halyard, a shackle must be used to attach the halyard to the sail. Sail in light winds, 2 - 4 knots. Adjust the halyard to get the foot of the sail on the deck about 200 mm aft of the tack. The jib cunningham should be just tight enough to take the slack out between the luff buttons. Mark this halyard position with a mark on the halyard. As it is hard to get a good view of the halyard cleat, it is often better to put the mark at the plate for the bilge pump. Pull the halyard up past the plate. Put one mark on the rope and one on the plate when they line up.
It is hard to judge the rudder angle when steering with pedals. Put the rudder straight when the boat is on land. Pull the rudder lines tight and mark the lines at a point where they are visible when sailing. Put marks at ½ inch distances forward and aft of the original mark. When the rudder lines are on one of the ½ inch marks, the rudder angle is approximately 4 degrees.
The helmsman’s position, in the 2.4mR gives him/ her a perfect "sailmakers view" of the sail shape. Therefore, we use both the angle of the top batten relative to the boom and the leech telltales as references for sheeting. In very light conditions, around 2 knots, the top batten should point a few degrees to leeward to help the wind pass over the sail. When the wind increases to 4 - 8 knots the mainsheet is adjusted to make the top batten parallel to the boom. The telltale, at the top batten, is then flowing about 60% of the time. At 10 - 14 knots the mainsheet is kept the same and the leech is opened by pulling the backstay. If the seas are rough, the mainsheet can be eased a little. In smooth waters and even wind strength, the sheet can be pulled a little tighter to focus on pointing. In winds over 14 knots, when the backstay is pulled to 4 or 5 units, the mainsheet is pulled so that the top of the sail luffs in the bigger waves but the leech of the sail keeps flat without luffing.
Mastbend Inducer/ Restrictor
In very light conditions up to about 4 knots, the mastbend inducer is used to make it possible to bend the mast and at the same time keep a relatively loose forestay. Bending the mast gives you a mainsail with less depth and open leech. That way the wind is flowing over the sail with less drag.
When the wind is stronger than 14 knots, the mastbend restrictor is used to prevent the mast bending too much in the lower part. When the mast and the luff curve is the same, at about 4.5 units backstay, slight over bend wrinkles start to be seen from the middle of the mast to the clew. When the restrictor is set, more backstay tension will twist the mainsail and increase forestay tension without bending the lower part of the mast too much.
In up to 4 knots, when the mastbend inducer is set, the backstay primarily defines the headstay sag (see further under jib trim). The right amount of sag, and mast bend, is achieved when the top of the backstay is pulled to about 2 units. When the wind increases, the bend inducer is released and the backstay tension is increased. The determining factor for backstay tension is the helm of the boat. This means that the backstay is the most important adjustment when sailing in varying wind strength. As soon as a tack (or other maneuver) is finished, get your hands on the backstay adjuster and keep the boat in balance. Keep an eye on rudder angle!
At 10 knots, the backstay is at around 3 units, and at 14 knots around 4 units. In winds over 18 knots, the backstay is pulled to 4.5 - 5 units, and if the wind is increasing to over 24 knots, the backstay can be pulled even a little more. In survival conditions, don't worry about how the sails look but how the boat feels!
Cunningham affects the camber position. In light winds, the mast is relatively straight and therefore the main is enough draft forward without using cunningham tension. Short horizontal wrinkles are seen along the luff of the sail. When the backstay is pulled to 3 units, the cunningham is set just enough to make the wrinkles disappear. If the wind is puffy, adjust the cunningham for the lighter winds and cleat it. It takes a few seconds for the draft position to move back when the cunningham is eased and its easy to get out of rhythm with the puffs if you adjust cunningham too often. In strong winds, the cunningham is used to keep draft position forward. The exact amount of cunningham tension varies with the age of the sail. A new sail needs less cunningham than a sail with many sailing hours. The rule of thumb is to keep the camber position at 50% of the cord length. In winds over 18 knots, the cunningham should be pulled real tight.
Outhaul adjustment is not as sensitive as cunningham. Up to 4 knots, the distance between the boom and the foot of the main is about 50 mm (2 inches). At 8 knots, the outhaul is pulled so the slot is closed, and at 12 knots the outhaul is pulled to create a wrinkle along the boom. At this point, the clew (which is impossible to see) is all the way to the black band at the end of the boom. It is important to have the tack attached to prevent it from moving aft as outhaul tension is increased.
The main traveler is always kept in the middle. We have tried to use the traveler to keep the boom on the centerline in light conditions and also to let the traveler down to leeward in heavy winds. Neither has proven faster than keeping the traveler in the middle. It is just two more lines to worry about.
Up to 14 knots, the jib leech should be 1.5 units out from the spreader tip. If you need to point extra high, you can sheet the leech all the way in to the spreader a short while provided you feel that the speed is sufficient. If the priority is on speed rather than pointing, the sheet can be eased to make the distance between sail and spreader to about 3 units. In rough seas the leech can be between 3 and 5 units from the tip. The barberhauler does not normally need adjustment in winds under 14 knots; it is enough to use the jib sheet. In winds over 15 knots, the barberhauler is gradually eased to increase twist. At 22 knots, the jib leech is about 10 units from the spreader tip.
The foot of the jib should not be too deep. The barberhauler has the same position in winds up to 14 knots. In light winds, the foot of the sail is all the way out to the edge of the deck. At 5 knots, the foot is at 3 units on the decal on the foredeck. From 8 knots and up, the jib is almost straight at the foot, at 7 units. If you need extra speed, ease the sheet a little to open the leech which will also make the jib a few units deeper at the foot.