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J/30 Rig Tuning

Jump to Sections to read online or download:

UK-Halsey Guide

North Sails Quick Tuning Guide Version 1.0

North Sails Guide

Banks Sails Guide

Shore Sails Guide – Scanned Document (Download Only)

Loos Gauge Conversion Chart for Model B and PT-2

UK-Halsey Tuning Guide

J/30 Tuning Guide – Download the UK-Halsey Tuning Guide in Word

Mast Tuning

The objective of our tuning system is to maintain consistent pre-bend in all conditions. This will enable you to have the greatest range of headstay tension possible, while insuring that the mainsail luff curve fits the mast bend characteristics. This tuning system is not unique, but common on any fractionally rigged boat with swept-back spreaders, but no running backstays. The mainsail luff curve must be designed with the minimum prebend approach to rig tuning in mind, or else the sail may be too full in its lower sections. The J/30 relies on tight shrouds with nearly equal tension on uppers and lowers to minimize headstay sag.

1) Forestay length should be set to the class maximum: 35′ 10 ½ ” pin to deck centerline at the sheer-line. This means that the maximum luff length (measured using a tape measure on the uppermost genoa halyard hoisted all the way up, down to the bearing surface of the tack horn) will be approximately 35′ 2″. The turnbuckle will probably be at its maximum extension.

2) Remove partner blocks and center mast with upper shrouds. Use the main halyard to equi-distant points on either rail as a guide. Take-up on the lowers just enough to keep the lower mast in column with the top (hand tight).

3) The mast step should be maximum forward (so that the forward edge of the mast is 25mm aft of the forward vertical face of the molded step in the sole liner. Block mast in front, pushing it as far aft as possible in the partners. This will reduce prebend in the lower mast sections.

4) Adjust wooden blocks so as to fit snugly on either side of the mast partners. Shimming and/or planning may be necessary, as there is a good chance that the mast will not be perfectly centered in the partners.

5) Take- up the backstay turnbuckles evenly, (you will probably have to bottom them out), until the twin bridle blocks come to rest just below the connector plate where the split backstays join. With proper tension, the backstay adjuster should spring to this point when the backstay is released. Usually, you have to shorten the primary backstay wire 3-5″ to be able to get it tight enough.

6) Tension the uppers and lowers gradually and evenly (counting turns as you go), until there are approximately 1800 lbs. On each, as measured with a Loos tension gauge. Start with the uppers, adding just enough tension on the lowers to keep the mast in column as the uppers get tight. Put final tension on the uppers with backstay fully on. Release backstay, and put final tension on the lowers. As you tension the lowers the pre-bend will be reduced (they pull back on the center of the mast). Tighten until pre-bend is no more than 2-3″.

7) Upper and lower tension should now be close to even. This should leave you with about 2″ of pre-bend (it probably looks like more, but you can measure it by putting the mainsail halyard against the back side of the mast, and subtracting 2″ from what you see). Tighten the lowers to reduce pre-bend (make mainsail fuller), let off to increase, (flatten mainsail). Conditions and mainsail shape will dictate the correct amount of pre-bend.

Simply stated, the tighter the overall rig tension, the greater the headstay tension; as long as the tension is nearly equal on uppers and lowers. In lighter air, when more sag is desirable, ease both shrouds slightly, and ease the lower shrouds more than the uppers to allow for more pre-bend. In heavier air, use more tension (2000 lbs) on both; the lowers should be as tight or tighter than the uppers to reduce pre-bend.

J/30 Upwind Sail Trim

As a first step, mark all control lines (halyards, sheets, genoa tracks, backstay, outhaul), in order to be able to duplicate settings from race to race, or leg to leg; and also to know exactly how the boat was set up when you found yourself going fast! Do not be afraid to vary settings. The numbers are a guide, not the law. Sail trim is always dynamic, and you must be shifting gears constantly. Keep an open mind.


Check to make sure that each batten is positioned squarely in the pocket, tapered end in first. If you have two or more full-length battens in your sail, see that the battens are square in their inboard end fittings, and tension via outboard-end control system just enough to pull cloth smooth and tight along the length of the batten.

-Use the top hole in the tack pin fitting.

-If you have a flattening reef lead it from the sheave, up through the grommet, and back down to the extreme outboard end of the boom. Slip it under the clevis pin where the topping lift attaches, and dead-end with a figure eight or double overhand. The newest mainsails have flattening reefs.

-Make sure that the sail is fully hoisted. When the head is at the black band, the luff should be smooth, with just the beginning of horizontal wrinkles in the lower sections of the luff.


THE MOST IMPORTANT CONTROL! Trim the mainsheet hard enough to make the top batten parallel to the boom. You can check this by sighting from underneath the boom on a vertical plane. The top telltale should be stalling periodically.

In smooth water and high pointing conditions, trim slightly harder to cock the top batten slightly to weather. (This should stall the top telltale). If the mainsheet is too tight, the boat will point well but slow down. Anytime you need to accelerate, or whenever the air is light or the water choppy, the top batten should twist off slightly from the normal position, and all the telltales should flow. Remember: SPEED FIRST, THEN POINTING.

As the breeze picks up you will find it necessary to use quite a bit of mainsheet tension to keep the top batten from falling off. In very strong, puffy, conditions, strap the vang on hard to assist the mainsheet. (This is referred to as “vang sheeting”). This will enable you to play the mainsheet and the traveler in the puffs to keep the boat on its feet.


The traveler has two functions: to control the boom’s (and the sail’s) angle to the wind, and to steer the boat; controlling helm and heeling in the puffs and lulls. The boom should be set on centerline for maximum power and pointing, as long as helm and heeling are under control- usually up to about 12-14 apparent. This means that the traveler car will be set to windward of the centerline in light to moderate conditions, gradually dropping as breeze and mainsheet tension increase. It is the position of the boom that counts, not the traveler car.

As the breeze increases drop the traveler to keep helm and heeling under control. In moderate conditions, you will be able to play the traveler to keep helm and heeling under control. In moderate conditions, you will be able to play the traveler (up in the lulls, down in the puffs) to keep the boat on its feet.

The lower the traveler the faster you will sail. Try to sail with as little helm (traveler down) as possible, while maintaining pointing. With the traveler up you will get plenty of feel (what we call “training wheels”), but you need to be careful of slowing down.

Outhaul/ Flattening Reef

The outhaul and flattening reef (really a “super” outhaul) control the fullness or power in the lower third of the sail. Upwind the shelf or “twist” foot in the mainsail should never be fully open. Upwind the bottom of the main should always be flatter than the top. As a guide, you can use the following procedure to set your outhaul/flattener controls:

1) Pull the outhaul on as hard as it can go and cleat it. (Cloth will be gathered in a tight crease along the boom). Put a mark on the line just in front of the cleat, and a corresponding mark on the boom (#1) to line it up with. This is your maximum position.

2) Ease the outhaul so that the foot is fully open, but not so far that it is bunching or forming vertical wrinkles along the boom. Mark the boom directly above the mark you put on the outhaul control line (#4). This is your minimum outhaul position, used only when sailing off the wind.

3) Put two additional marks on the boom, spaced evenly between the maximum and minimum marks, and label them #2 and #3. For different wind strengths, the line reference mark will correspond to the marks on the boom as follows:

Outhaul Guide

Apparent Wind                                             Outhaul

0-7                                                              #3 (eased)

8-13                                                            #2 (tighter)

14-18                                                          #1 (max tight)

18 +                                                            Flattening Reef

As the breeze dies, or when you need extra power to sail through the waves, the outhaul can be eased slightly from normal settings. In puffs or smooth water, it can be tightened. Notice that the minimum position (or fullest) is never used upwind. This position is for reaching and off the wind work only.


The Cunningham, along with the main halyard provides luff tension, which controls the fore and aft position of the camber in the sail. A good rule is to use just enough luff tension (main halyard first, till the black band is reached, then Cunningham), to smooth the horizontal wrinkles out of the luff of the sail. Leaving a few wrinkles in the bottom of the sail is fine. This should keep the maximum camber at or just forward of 45% in the sail.

As the breeze increases, you will need more cunningham.  Whenever you add backstay, you will probably need more Cunningham. Smooth all the wrinkles out only in windier conditions. As your main gets older it may need more luff tension to keep the draft far enough forward.

Boom Vang

Upwind, the vang assists the mainsheet in pulling down on the boom and providing mainsail leech tension. Use no vang up to about 10-12 apparent. From this point snug the vang up, gradually tightening it as the breeze increases. By the time you get to 18 apparent it should be very tight. In a breeze, vang tension will help bend the mast down low, and will allow you to play the mainsheet in the strong puffs (vang sheeting), as described above. The only exception to this technique occurs in very choppy conditions, when extra twist (less vang), may be faster.


As the wind increases above 7 apparent, tighten the backstay correspondingly. Backstay tension does two things. First, as the mast bends the upper two-thirds of the mainsail flattens and the leech opens up- both of which relieve helm and heeling. Second, increased backstay makes the headstay tighter, flattening the headsail and opening the leech up- increasing pointing ability and reducing heel.

Since adjusting the backstay has a large and immediate effect on mainsail leech tension, mainsheet tension should be adjusted at the same time. More mainsheet as you add backstay, less as you ease. Next adjust the traveler accordingly, and check the Cunningham. It is a continuous loop, with each control affecting the other.

Assuming minimum backstay tension when the blocks are at rest below the split backstay connector plate, and maximum tension when the blocks are level with the stern pulpit, you can use the following percentages as a guide.

Backstay Guide

Apparent Wind                                 Backstay

0-7                                                             min.

8-10                                                           25%

11-14                                                         50%

15-18                                                         75%

18+                                                            max.

Genoa Trim

Which sail to use?

The J/30 is a relatively underpowered boat for its displacement and wetted surface. The boat will carry its class 163% genoa up to about 20 apparent. In the heat of the battle J/30 sailors have been known to carry the #1 in even more breeze than that; though for the sake of the sail’s shape this practice should not be encouraged. Obviously, the heavier the crew, the more wind you will be able to carry the big genoa in. We sail with either a gargantuan five, or amore normal six or seven. Maximum legal all-up crew weight is 1400 lbs. This much weight will not hurt in light air- it may even help-, as long as it is kept in the right place.

The #2 (140%) genoa is useful in a narrow range from 17 to 26 apparent. In our opinion this is an under-utilized sail. With a reefed mainsail and #2 the boat is surprisingly effective- even though this defies convention given the boat’s fractional rig. The added power of the #2 will help drive through waves and chop.

Normally however, we would recommend switching to the #3 (105%), over 24 apparent. The perennial J/30 question concerns which combination is better; a full main and a #3, or reefed main and a #2. There is less difference than you think, and much relates to personal sailing style. If the water is smooth or there are big even swells, use the #3. For the short lumpy stuff, try the #2 and a reef. Above 26 apparent definitely calls for the #3. Over 33 apparent, use a reef and a #3. One possible sign of being underpowered is if you find that you have speed with your competitors, but can’t seem to point quite as well. This is particularly true when using the #3 against boats with a #2.

Halyard (Luff) Tension

The golden rule- use just enough halyard to smooth the horizontal wrinkles out of the luff of the sail. You will need more tension with more breeze. It’s better to have too little luff tension than too much. Start with wrinkles, then just barely smooth them out. In smooth water, leave a few wrinkles for finer entry and better pointing.

Lead Position

The sheet lead should be set so that the sheet applies roughly equal tension to leech and foot.

The standard method of determining lead position is to head up slowly and watch the sail luff. It should luff relatively evenly along its length. The top will break slightly before the bottom! If the top breaks too early, move the lead forward. With the lead in the correct position, the sail will be roughly the same distance off the spreader tip, as it is off the shrouds at the chainplates (maybe a little closer at the bottom). This should be the median lead position. It should be adjusted as you move from the bottom to the top of the sail’s wind range. Move the lead aft to depower (top of the range), forward to power up (bottom of range). Basically as it gets windier and you sheet in, the lead will move aft. Decreasing velocity will require a sheet ease and lead forward. In order to fine tune your lead position you will need to drill extra holes in the track, midway between the factory holes. Use 6 holes, spaced approximately 2″ apart to cover the whole range of a genoa. The holes are numbered appropriately: 1-6, with 1 being forward, and 3 being the median setting.

Better to have the lead too far aft than too far forward. A rule of thumb is that whenever you need to drop the mainsail traveler to keep the boat on its feet, move the jib lead aft. If you have excessive backwinding, and you have flattened your main, move the lead aft.

Sheet Tension

The genoa sheet is the gas pedal and must be played constantly, easing to accelerate, trimming to point. The sheet tension will vary with every change in velocity. Use the distance off the spreader tip as a guide. (see the table below for approximate distances) After about 14-16 apparent , if the breeze is fairly steady, move your trimmer up to the weather rail. Their weight is worth .1 of a knot. They can dive down and make adjustments for the big changes. REMEMBER: SPEED FIRST, THEN POINTING.

Genoa Trim Summary

Apparent Wind      Lead                          Sheet                     Luff Tension

0-3                                        1                                 8-12″                       smooth

4-7                                        2                                 3-5″                         smooth/slight wrinkles

8-13                                      3                                 1-3″                         slight wrinkles

14-17                                    4                                 1-4″                         smooth

18+                                       5-6                             4-10″                       smooth

Use just enough leech cord to take the flutter out of the leech.

Weight Placement

Crew placement on the J/30 reflects two design characteristics of the boat. First the keel is small for its sail area. Second, the boat tends to sit down in the stern, a problem compounded by the fact that maximum beam (wetted surface) is carried well aft. This means you have to work on keeping crew weight well forward in most conditions. There is a natural tendency to congregate in the cockpit which must be discouraged. ( There are some boat control system changes which can really help. Give us a call and we’ll be happy to go over some of the standard modifications).

In light air, upwind and down, the crew should be up by the shrouds, or huddled at the base of the mast. Heel the boat as much as possible. If you have a particularly dedicated crew, send all but the primary trimmer down below. It makes a remarkable difference. As the breeze increases the crew can gradually move up to the rail and aft to the point of maximum beam. The only time you need to move aft is on tight spinnaker or jib reaches, when you are at maximum heel or beginning to get overpowered.

From experience you will find that the boat like to be sailed as flat as possible. Translated, this means as flat (or with a little feel to the helm) as the driver can stand and still keep the boat in the groove. This will keep the small keel in the water and doing its job. The boat will get a mushy-almost slow-feeling just as it really gets hooked up. Sometimes, if you have it going, you can sail virtually upright even in light air. This should be your goal. Careful, as soon as you feel slow, put the heel back on. Make sure the boat is well heeled out of tacks and through waves.

A well-trained crew will react to changes in velocity and the fell of the boat automatically. Moving to leeward and forward if the breeze dies or the boat feels slow, and back up to weather when the boat heels over, or when the driver gets dialed up. The helmsperson should constantly communicate, and let everybody know how much heel the boat needs.

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J/30 Quick Tuning Guide for North Sails Version 1.0

Download the PDF Document with this North Sails J/30 Quick Tuning Guide

North Sails Quick Reference Guide – Version 1.0
Wind V1 (Caps) D1 (Lowers) Headstay turns from 0
Base Setting 1050 950 15
Light (0-7) 450 250 10
Medium (8-12) 1050 950 15
Medium/Heavy (13-17) 1600 1600 20
Heavy (18+) 2000-2200 2000-2200 20-30
Pt2 Loose gauge – all turns are from base settings

J/30 Tuning Guide for North Sails

Download the Word Document with this North Sails J/30 Tuning Guide

The tuning set up that follows is designed to be as “all purpose” as possible. Like many one designs the J/30 uses just a few sails to cover a wide range of wind and sea conditions. Set you boat up the way we have described here and you will have excellent speed in all conditions.

Section 1. With the Mast Down

1) The spreader brackets and mast may need to be repaired or reinforced to prevent the spreader brackets from pulling away from the mast. Reinforce the spreader brackets using a metal strap welded, bolted or riveted to the spreader brackets and going around the front of the mast to connect the brackets. Internal support structures such as bars or plates may also be used and spreader brackets may be bolted through the mast. Tape the spreader ends.

2) Check the main, spinnaker, and headsail sheaves. Wire halyards tend to cut into the sheaves. When you replace the wire halyards with hi-tech line, worn sheaves will chafe the new lines almost instantly.

3) Check your mast markings. Measure down the mast from the base (include shoe thickness) to the lower edge of the upper black band as described in the class rules (< 14280 mm < 46’ 10 3/16”). The upper edge of the lower measurement band on the mast shall not be more than 2698 mm above the surface of the molded mast step.

4) We want the headstay as long as possible. To check this after the mast is up, attach the headstay and hold it alongside the front of the mast and make a mark on the headstay corresponding with the mast band mark in Rule 5.7.2 (2698 mm above the surface of the molded mast step). Max headstay length is 10935 mm when measured from pin to intersection of stem and sheer as shown in the following diagram. (See figure 1.)

5) Before stepping the mast, move the forward edge of the mast butt shoe 25mm (1”) from the molded mast step per Rule 5.7.3

Section 2. Mast Up

Step the mast and attach all shrouds (except the backstay) very loosely. Leave any mast blocks out for the moment.

1) Next we need to make sure that the mast is positioned as far aft at deck level as possible. Have a friend hold the end of your tape at the stem measurement point and measure again straight to the forward edge of the mast. We want this measurement to be as close to maximum as possible, Stem to front of mast (J) 3505 +/- 13mm, (11′ 6” +/- 1/2”) per Rule 5.7.3. Chock the mast at the deck to hold it in this position. See figure #1 to determine measurement point at stem.

2) Get the mast and the keel in line.
It’s important to get the mast and the keel on the same vertical plane. If the boat is out of the water, (the boat does not have to perfectly level) place a ladder approx. 100 feet behind the boat. The ladder must be placed directly behind the boat (as close to the extenuation of centerline of the boat as possible). Next tie a string from the top rung of the ladder to a low rung. Accurately, align the string with the trailing edge of the keel then sight up the string to the top of the mast (adjust the string horizontally on the latter rungs). Ultimately the top of the mast and the sail grove should be in line with the trailing edge of the keel. This should all be done with no blocks in at the partners. To get a proper sight put one knee down and try and stabilize your body as much as possible than just use one eye to glance up to the top of the mast and back down to the keel. Having a friend with you to confirm what you are seeing is not a bad idea. When you are confident that the mast and the trailing edge of the keel are on the same vertical plane then check to make sure that you are at the max J dimension. Now you are ready to put the mast partner blocks in.

If the boat is in the water, center the mast by tighten the upper shrouds to ___ on a Loos Model B tension gauge and the lowers to ___. We get the uppers snug first and then using a metal tape measure attached to the main halyard measure down to the rail adjacent to the chainplates on both sides. The measurement should be the same on both sides to be sure the mast is centered in the boat. Be sure to sight up the backside of the mast to be sure the mast is not bowed. If bowed, adjust one or the other lower shrouds to straighten the mast.

At this point your mast should be set up with __- ___” of prebend in the mast. To check this simply hold the main halyard at the gooseneck and sight up the backside of the mast. If this is not the case you’ll need to go back and recheck your measurements.

Section 3. Tuning Chart

As we mentioned before, the J/30 has just 5 sails to cover the entire wind range the boat is raced in. The Number 2 Genoa is seldom used. For the best performance in each condition we adjust the tension on the shrouds depending on how much wind there is. As the final step in setting up your boat fill in the attached tuning chart with how many turns of the turnbuckles it take to get from one setting to another. Counting turns allows adjustment of the shroud tension during races when it is impossible to the get accurate Loos readings with the sails up and the boat in waves.

Rig Settings

Old Loos Gauge Model B

Wind Uppers
0-5 ____ ____
6-9 ____ ____
BASE 10-13 ____ ____ BASE
14-17 ____ ____
18+ ____ ____

New Loos Gauge Pro Model PT2


0-5 ____ ____
6-9 ____ ____
BASE 10-13 1500 1000 BASE
14-17 ____ ____
18+ ____ ____

Special note on the backstay: As you adjust the tension of your lower shrouds you’ll notice the backstay gets tighter or looser. Each time you adjust your shrouds be sure to adjust the two smaller backstay turnbuckles so that the blocks riding on the backstay bridles stay 6-8″ below the “y’ in the backstay when the tension is off. This is very important to make sure the headstay can get tight and loose enough depending on the conditions.

Sail Trim:

Follow these guidelines to set up and trim your sails.


Outhaul: From the clew to the mast black band:

Wind Inches
6-9 ____
10-13 ____
14-17 ____
18+ ____

No cunningham until about 12 knots, then tension until wrinkles in luff are just removed.

Upwind keep loose to 8 knots then tension to remove all slack above that. Above 15 knots tension very hard so boom does not rise at all when the mainsheet is eased.
Downwind tension so top batten is parallel to boom.

Keep all the way up on weather side until crew is all sitting out on weather side with legs out. As soon as crew is on weather rail with legs over, drop down 2″. Then drop it down as far as the middle of the track to keep the boat flat. If you have to drop below middle to keep boat flat put on some backstay and keep traveler in the middle. Play traveler in puffs to keep boat flat as wind builds. We do not like to sail with traveler below ¾’s of the way down.

Use to control fullness on main and genoa. Leave loose until about 8 knots. Slowly tighten as breeze builds to depower boat. At it’s tightest, it will be all the way down to the top of the pushpit. A small adjustment (1-2″) can have a big effect here. Be sure to adjust the backstay turnbuckles when adjusting the side shrouds.

Tension mainsheet so top batten is parallel to the boom and the top telltale is flying 50-60% of the time up to 10 knots of wind. Above that the top telltale should be flying all the time because now the top of the main will be flatter.

Mainsail Setting Chart

Wind Speed Traveler Backstay Top batten angle Outhaul
0-6 knots All way up None Closed 3 degrees In 1/2″
7-12 Down 3-4″ 1/4 on Closed 3 degrees to parallel Max tight
12-18 Middle 1/2 to 3/4 on Parallel to open 3 degrees Max tight
18+ Below CL 2-3″ Max on Open 3-6 degrees Max tight

Genoa set up:

With the genoa there are three major things we are concerned with, having the lead in the proper position, having the genoa halyard set right and getting the sheet tension right.

Halyard Tension:

We want to the halyard set so the luff of the genoa has just a hint of wrinkles in it. The reason is that we have found that it is better to have the halyard too loose rather than too tight. In light air we want to be sure that the luff is nice and loose. As the wind builds, we tension the halyard enough that the cloth along the luff of the genoa is smooth.

It is important to have a mark for your genoa halyard near the stopper to keep it in position. We mark off ½” increments to make it easier to duplicate fast settings. Also mark the sail luft at the mark on the headstay that corresponds to the lower mast band mark (see Section 1 #4).

Lead Position:

Note that it is important that you have drilled out an extra set of holes between each of the factory-drilled holes in your genoa track. The standard spacing is too far apart to be workable.

Having the lead in the correct position is critical for good speed. In moderate breeze (4-8 knots), trim the sail in and position the lead car so that the sail touches the spreader and the chainplates or turnbuckles at exactly the same time. Mark this position. This will be your neutral point for your jib lead.

Sheet Tension:

We check the sheet tension by judging how many inches the sail is trimmed away from the end of the spreader. Generally we never trim the sail tighter than 1″ from the end of the spreader.

Genoa Setting Chart

Condition Lead Halyard Sheet
0-6 flat 1 aft of neutral Wrinkles 3-4″ off spreader
0-6 choppy On Neutral Wrinkles 3-6″ off spreader
7-13 flat On Neutral Just Smooth 2-3″ off spreader
7-13 choppy 1-2 holes fwd. Wrinkles 2-4″ off spreader
14-18 choppy 1-2 holes fwd. Smooth 4-6″ off spreader
18+ On neutral Tight 6-8″ off spreader

As the above chart shows it is important to change your settings depending on the condition. Be aware that as the wind builds and dies you will need to be constantly adjusting the tension on the genoa sheet.

Class Jib Trim:

Lead Position:

Drill two extra holes between each set of factory holes in the jib track. Start with the jib lead block positioned at the chainplates and fine tune the lead position from there.

Halyard Tension:

Unlike the genoa the luff of the jib should always be smooth. Be careful, you can in moderately heavy air get the luff too tight. The luff of the sail should break evenly up and down. If the sail breaks high first move the lead forward, low first move the lead back. Check this carefully and make a mark on the deck in the correct spot. Also mark the sail luft at the mark on the headstay that corresponds to the lower mast band mark (see Section 1 #4).

Jib Sheet:

Sheet tension is critical. We like to adjust the tension on the jib sheet to balance out the helm of the boat. If the boat has a bit of weather helm trim the jib slightly to pull the bow down. If the boat has leeward helm ease the jib slightly. Keep in mind that you only need to change the tension on the sheet very slightly (1/2″ increments) to have a real effect on the trim of a high aspect sail like the jib.

Spinnaker Trim

The spinnaker should be at full hoist at all times. The general rule of trim is to allow 2-4″ (50-102 mm) of curl in the luff of the sail. The ends of the pole should be even with the free floating clew and the pole should remain perpendicular to the apparent wind. If you are going slow try raising the pole a couple of inches.

Downwind-light air: Concentrate on good communication between helmsman and spinnaker trimmer. The goal is to sail as low as possible while still maintaining good pressure in the spinnaker (measured by tension on the sheet). Try not to sail too high which translates into longer distances, but do not sail too low at a slow pace. Be careful not to pull the pole too far aft which flattens the spinnaker.

Downwind-heavy air: Be careful not to square the pole back too far as this makes it easier for the spinnaker to roll out to weather. Do not let the clew of the spinnaker go past the headstay. Keep most of the crew hiked on the leeward side in order to sail low and not risk rolling to weather.

Downwind tips:

1. Pole height is important and changes in increments of 1″ (25 mm) have a big effect on the spinnaker. The break in the sail should curl evenly from top to bottom. If the spinnaker breaks high, the pole is too low and should be raised. If the break is low, the pole is too high and should be lowered.

2. Whether or not you use tweakers (or twings), an efficient foreguy system is crucial. Every up and down, or back and forth motion of the pole (and hence the spinnaker) is wasted energy; that energy will not be pulling the boat forward.

3. An efficient system for launching and retrieving the spinnaker is a must. We recommend a rail mounted launching bag, or launching from the v-berth hatch. Call us if you would like a launching bag made for your J/30.

In conclusion:

  • Always sail the boat as flat as possible except for very light air
  • Sail as close to max weight limit of 1400 lbs as possible see Rule 6.7.1.
  • Do not be afraid to change settings if you are slow.
  • Keep a tuning chart and use it.
  • Have open positive communication on board.
  • Sail fast and have fun!

For tuning help, contact the North J/30 experts.

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Banks Sails J/30 Tuning Guide

Download the Banks Sails Tuning Guide in Word

Last update: Jan. 7, 1996 (Copied from Old J/30 Website)

Preliminary Info Before you tune the rig to these numbers make sure that the head of the spar is centered over the boat. Hoist the tape measure on the main halyard, measure from port chainplate to starboard chainplate. The number should be the same (to within 1/8th inch.) Once you have centered the rig, then proceed with setting up the rig to the following numbers.
J Measurement 11′ 6″
Make sure your mast is blocked all the way aft in the partners. With the tape measure pinned at the intersection of the forestay and the stainless steel stem fitting at the deck, the front edge of the mast should be as far aft in the partners as possible. 11′ 6″ is the maximum legal “J” dimension and is most desirable for inducing some weather helm and enhancing pointing ability.
Headstay Length 35′ 10 1/2″
A pair of binoculars will come in handy to sight up to the hounds (forestay attachment point on the mast). Measure this by hoisting a metal tape measure up on the spinnaker halyard so that the tape is even with the headstay pin. Then measure down, along the headstay, to the stainless steel plate on the deck. (not to the forestay clevis pin)
Mast Butt Position With the headstay at max. length of 35′-10 1/2″ and the mast blocked all the way aft in the partners for maximum “J” dimension, position the mast step so the mast is straight fore and aft with slack shroud tension (no pre-bend). When the following shroud tension numbers are used they will induce minimal lower mast pre-bend and a total pre-bend of 1.5 – 2″. This will transfer more load to the headstay for a tighter headstay and better all around windward performance. In addition it will make the mast bend top-loaded. This will make for a powerful mainsail in lighter air when minimal backstay tension is applied. As the breeze builds and you need to “shift gears” and flatten the sails, increasing backstay tension will tighten the headstay, flattening the jib and will flatten the mainsial and twist off the top of the main providing a smooth progression from fully powered-up to de-powered.
Shroud Tension Uppers: 44 – 45 on the Loos Tension Gauge.
Lowers: 45 – 46
Helpful Hint Pull the backstay on to maximum before you try to tighten the upper and lower shrouds. Doing this will pull the masthead aft in the boat, easing the tension on the shrouds and making it easier to increase tension on the rig. Just make sure that you ease the backstay off when you check your rig tension numbers on the Loos gauge.
If you tune to these numbers you will have a pretty tight rig. With the backstay all the way eased you should have about 1.5 – 2.0″ of pre-bend. The headstay should be just barely snug. This should provide enough headstay sag to power up the genoa for all but the lightest sailing conditions. As the breeze increases so will your backstay pressure. This will increase headstay tension and flatten the entry of the genoa. As you probably know, the J/30 is power-hungry. You won’t have to use much backstay as the boat can use as much power as it can get. Until the wind howls and you’re well into the #2 and #3 jibs you will use backstay sparingly.

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Loos Gauge Conversion Chart for 90 Model B and PT-2

Download the Loos Gauge Conversion Chart as an Excel Spreadsheet

Loos 90 Model B

Pounds Tension

Loos PT-2

Pounds Tension

1/4" 1×19 Gauge Reading


1/4" 1×19 Gauge Reading










































































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