420 Tuning Guide

Congratulations on your purchase of North Sails! The following tuning guide for the International 420 is the result of many years of sail testing, rig tuning and racing in every conceivable condition. You can follow this guide with confidence.


Measured from the inside of transom to the back of the mast 2830 mm.


Length is measured from the sidewall of the mast to the shroud.

To measure spreader deflection we place the top batten (or any straight edge) across the tips of the spreaders, and then measure to the mast off straight edge.




Superspar M7

470 mm

162 mm

Proctor Kappa

480 mm

160 mm


470 mm

165 mm


Measured by attaching a long tape measure to the top of the main halyard, hoisting it to the top of the mast & then measuring to the back of the transom with the rig tension on & NO CHOCKS inserted.

NB – if caught out on the wrong mast rake you may want to either ease or add tension accordingly to achieve the best setup.


Control the amount of pre-bend in the mast. This is crucial for controlling the amount of power in the rig.

You should have 3x 15 mm chocks, which are easily accessible, as chocking the mast is the only adjustment you can make to the mast whilst racing.



0-6 Knots


6-11 Knots


12-16 Knots


20+ Knots



This should be angled forwards in light air. When planing upwind the leading edge of centerboard should be vertical, as the wind increases the centerboard can be raked aft (no more than 6 inches of centerboard handle showing out of the case).




2-6 Knots

19’9 3/4

7-11 Knots


12-16 knots

19’8 1/2

17-23 knots


24+ knots

19’7 1/2

It is very important to be able to get your boom as close to the center line as possible, so your mainsheet strop length must be altered depending upon the given conditions.



2-6 Knots

560 mm

7-11 Knots

555 mm

12-16 Knots

530 mm

17-23 Knots

525 mm

24+ Knots

525 mm




In light airs the top batten should be pushed in lightly and the velcro fastened just to prevent batten from falling out. In medium/heavy airs, push the batten in quite hard and secure the Velcro.


Use only when overpowered to move draft of sail forward and open the upper leech. Never use in light air to remove the horizontal creases from the luff.


No tension is needed until the mainsail has to be eased to prevent heeling. Use kicker to hold correct leech profile. When overpowered, pull on as hard as physically possible. NB – Ensure that you have the maximum purchase allowed by the class rules.


Generally pull very tight in all conditions, except in a light air chop when the outhaul can be eased approximately 25 mm.


This is determined by leech tell tale behavior. Generally the top telltale should be flying 90% of the time.


Whilst on shore it is a good idea to mark both jib sheeting and barberhaulers. Tie the boat down to the trolley and place on a beat. Sheet in both mainsail and jib from behind and look at the slot (gap between mainsail and jib). Because of the 420s have fixed sheeting angles, the slot is not as efficient as it could be. You are looking to get the slot parallel all the way up between the mainsail luff & the jib leech.

Make sure the jib is in tight, then ease it one inch and pull the windward jib sheet (barberhauler) on quite hard and cleat it. Doing this pulls the clew inboard about 3- 4 inches and creates a more efficient slot shape. Now with a waterproof pen, mark both jib sheets and barberhaulers so you can refer to these settings whilst afloat.

This method of barberhauling should be used in all conditions except:

VERY LIGHT AIR – Very light pull on barberhaul

HEAVY AIRS – No barberhaul


This should be tightened enough to remove creases from luff of the sail. It acts the same as the cunningham on the mainsail.


  1. Play the mainsheet at all times
  2. Barberhaul in all conditions, except the extremes
  3. Use as much kicker as possible in heavy airs
  4. Never use cunningham until overpowered
  5. Keep the boat flat at all times
  6. ENJOY IT!

If you have any problem tuning your 420 or any other questions on 420 sailing, do not hesitate to contact North Sails.


Your North Sails are constructed out of the best materials on the market today. We make sure of this by testing every roll of cloth we use. Through proper care and maintenance your sails will give you the performance you have come to expect from a North sail.

The most important factor for a long life for your sails is to watch them for signs of wear and tear in high load and chafe areas. Be sure to wash the sails off with fresh water and dry the sails thoroughly before storing. A dry, mild climate is best.

Excessive heart can cause problems with the sails due to the possibility of shrinkage. It is best to roll the mainsail and jib.


When hoisting and lowering the sail try to minimize the amount of creasing or wrinkling of the sail. Every time the sail gains a crease the cloth breaks down that much faster. Always have someone contain the leech and luff during these procedures. The battens can be left in the sail without any problems. Be sure to roll the sail down the leech so that the battens will not twist. This could cause damage to the battens.


When rolling the jib keep the battens perpendicular to the leech. Pay special attention to the battens and batten pockets for wear and tear.


This tuning guide only begins to cover all there is to know about racing the boat. The 420 team at North One Design has prepared a professional, in depth 420 racing clinic that you and your fleet will be interested in learning more about. In the course of a weekend you will learn more about racing your 420 than you could possibly learn in a season of racing on your own.