Setting up and tuning the J class

Setting up and tuning your J Class model with Bermuda rig.


The Nottingham 48 and the 60 are well designed models which in a good state of trim should be elegant, rapid and predictable on the water and a very satisfying model to sail. The underwater profile will resist the weed that is becoming a feature of summer sailing and which can be so frustrating for skippers of yachts will finned keels and separate rudders and the relatively shallow draft adds to the models versatility.

The model is fairly forgiving of poor sail trim but setting up the model correctly will add greatly to the pleasure of sailing it. Setting up a yacht and trimming it for the prevailing wind conditions is the subject of lengthy and protracted writing and my intention here is not to replicate these missives but to create a simple guide to how to get the most out of your model. For some this guide may be too simple but I make no apologies and hope that most readers will find the guide of use.

Basic principles.

The sails operate as two wings and are subject to the same rules of aerodynamics as an aircraft but unlike an aircraft the aerofoil shape of a sail can be altered to suit the wind conditions. These alterations are referred to as “tuning” the rig. There are two objectives in tuning the rig, to obtain maximum speed and also maximum control and the two objectives achieved together will get you round a course in the shortest time.

The 48 inch model is available with three rigs, A, B and C. The A rig has the biggest sail area and is cut to suit light winds. The B rig has a slightly smaller sail area and is cut to suit stronger winds whilst the C rig is often referred to as a “storm” rig. The operating parameters of each rig will overlap so that an A rig can be detuned as wind speed increases and the B rig can be tuned for more power as wind speed decreases. The most versatile rig for day to day use is the B rig as it can be tuned for most conditions. I don’t have a C rig as if the wind speed dictates the use of this rig it’ s probably time to go to the pub but serious racing skippers will have a C rig.

The sail is not just a flat sheet but consists of a number of panels. Each panel is cut and joined so that it will naturally try to adopt an aerofoil shape. Further, the luff of the sail is cut with a curve or arc so that when it lies against a straight mast the sail will adopt even more shape.

Initial setting up.

Place the mast in the mast tube and fix the shrouds and backstay. Attach the jib swivel so that the sails are relaxed with no tension in the shrouds and only slight tension in the backstay and jibstay. Back off the kicker on the mainsail boom and ensure the leech line is loose. Stand back and look at the rig. The leech of the jib should lie parallel to the mast and as close to the mast as possible and the mainsail boom should lie roughly parallel to the deck. At this stage ensure that the foot of the mainsail and jib is fitted a close to their respective booms as possible and that the jib boom is fitted as close to the deck as possible.

Increase the tension in the rig first by tensioning the jibstay and then with the backstay so that the top of the mast is firmly located against fore and aft movement. Nip up the shrouds so there is just sufficient tension to secure the mast against sideways movement. Nothing should be “tight” at this stage.

Adjust the foot of the jib and mainsail using the clew adjuster so that the foot is flat (but not tight) and adjust the luff of the jib and mainsail the same ensuring that there are no wrinkles in the sails. This should make a good starting point for tuning and you should ensure that there is sufficient room to adjust on all of the adjusters.

Adjust the kicker or vang so that the end of the mainsail boom is able to move up and down about 10mm. The kicker changes the twist in the leech of the mainsail.

Adjust the foot of the mainsail and jib so that the foot adopts a slight curve. Add a little tension to the leech line on the jib so that this too has a slight shape. The general rule of thumb is that the curve in the leech of the jib should match the twist in the leech of the mainsail

In general terms, you will want to achieve a “full” shape in both sails for light winds and as the wind speed increases you will add tension to the rig to “flatten” the sails.

Note that any adjustment you make to one part of the rig will require additional adjustments to the other elements of the rig.


Backstay. This has the biggest effect on the rig overall. Tension in the backstay is transferred through the mast, creating a bend in the mast, tension is transferred down the jibstay to the tack of the jib, along the jib boom which pivots on the jib swivel and so puts tension into the leech of the jib.

As you add tension to the backstay you will see the shape of the mainsail flatten as the mast curves forward in the middle. As the top of the mast moves aft the end of the mainsail boom will drop so add tension using a mixture of tension in the jibstay and tension in the backstay. If the mainsail boom drops too far it risks dipping into the water as the yacht heels in the wind which will upset the shape of the mainsail.

Kicker. Increasing the movement in the back of the boom will increase the twist in the mainsail. This will allow wind to spill out of the top of the mainsail, depowering the top part of the sail and improving control in windy conditions.

Main sail luff tension. As you increase the tension in the backstay the tension in the luff will reduce. Use the adjuster to add tension. The luff shouldn’t be tight, but should be tight enough to keep a straight edge whilst still being able to swing around the mast on the luff rings.

Clew adjustment. (Both the mainsail and the jib) Moving the adjuster forward will put more shape in the foot of the sail and also the lower part of the sail. More shape will give you more power but also increase the drag created by the sail. Less shape will reduce power for better control in higher winds. Try to keep a similar shape in the foot of both mainsail and jib.

Jib luff tension. As with the Mainsail, the tension should be sufficient to maintain a good shape in the sail without wrinkles but not so tight that it creates more tension than the jibstay.

Leech line. As you put more tension into the rig you will flatten the leech of the jib and reduce its power. Use the leech line to take the tension out of the leech and add shape to match the shape of the mainsail.

Shrouds. The main purpose of the shrouds is to stabilise the mast. Putting too much tension into the shrouds will emphasise the curve in the mast and distort the shape of the mainsail. You should add just sufficient tension to stabilise the mast. Mounting the shrouds further back on the chainplate will reduce curve that will be put into the mast by the power of the wind, thus retaining the original shape you created when the model was at rest. A second set of shrouds fitted at the spreaders will add more support to the mast as it comes under pressure from the power of the sail as wind speed increases.

Jib slot adjustment. The jib boom should be opened up by adjusting the loose sheeting so that the end of the boom points toward the chainplate on the deck as a start. The jib slot serves to accelerate air through the slot and over the mainsail and this increased airflow over the mainsail improves the efficiency of the sail and the speed of the model. If your slot is too narrow the forward part of the mainsail will distort, and loose its aerofoil shape, (known as backing) but if too wide the slot will have little effect. Adjustment on the 48 is something of a compromise but the 60 has a separate servo to adjust the slot on the water. At slower speeds with reduced airflow the slot is narrowed to increase the velocity of the air travelling through it. As the hull speed increases the mainsail will start to “back” under the pressure of both velocity of the air and the increased volume so the slot can be opened improving the efficiency of the mainsail

Mainsail boom adjustment. The mainsail sheet should not be tight when sheeted in. I adjust the end of the boom so that when sheeted in its about 10 to 15mm off the centre line. As a guide, I start by looking at the back of the mainsail which should be pointing in a direction so that the airflow from the sail is directed aft, along a line parallel to the centre line of the hull

Weather helm and lee helm. This term refers to the tendency for the model to point up into the wind and stall, (weather helm) or point away from the wind (lee helm) especially when travelling into the wind. The model is designed to be “balanced” ie, that it should track a straight line without radical movements to the rudder which creates drag and reduces speed. If you experience weather helm this can be solved by increasing the power in the jib/reducing the power in the main and if you have lee helm vice versa. Lee and weather helm is a response in the hull to the sails not being tuned to act together.

Tuning the sails should sort both lee and weather helm but if not you can change the weight distribution in the hull. The centre of effort of the rig is designed to be forward of the centre of lateral resistance of the hull. As the yacht heels in the water the curvature of the hull acts as a rudder and tries to steer the hull in a direction opposite to the heel, into the wind. Placing the centre of effort forward overcomes the steering effect of the hull but it’s a fine calculation and will be slightly different for each model. The answer to weather helm is to move the centre of effort further forward by powering up the jib or depowering the main, (preferred) or, moving the entire rig forward, or alternatively moving the centre of lateral resistance aft. This is achieved by adding weight to the back of the keel which puts more stern in the water and takes some bow out of the water.

If you have lee helm which cannot be solved by tuning you can add weight to the forward part of the ballast which will put more bow in the water and take some stern out of the water, moving the centre of lateral resistance forward.

This is a radical solution and before you embark on changing the weight distribution I suggest you talk to me first as the tuning of the rig is likely to be the prime suspect of lee and weather helm issues.

You may find that as the model is accelerating (eg, having just rounded a buoy and sailing into the wind) and is heeling in the wind, that the hull tries to turn around the mast. This is often confused with weather helm but issues relating to weather helm and lee helm are better assessed when the hull is up to speed. This perceived weather helm is caused by the sails accelerating in an environment where there is little resistance and the hull, subject to the resistance of the water, has yet to catch up with momentum of the sails. This causes the hull to continue turning into the wind even if you have applied opposite rudder.

There are a number of solutions, all to do with how you sail the model, not necessarily tuning. The first is to straighten the rudder when half way round the buoy and let the hull do the rest (a straight rudder creates less resistance and the hull will accelerate more quickly). The second is to operate the sails with less vigour, bringing the sails to their final position for the run more slowly. Or a mixture of the two above. Maximum speed and maximum control are achieved by making slower, measured and progressive movements to the controls.