TUNING TIPS

Now that you have your new sails, how can you make sure you get the best performance from them? Sail setting is a science and an art form. The science is in designing the shape, and the art is in getting the sail set on your boat consistently.
 
Sail setting takes a lot of practice to get right, and especially to get right on a consistant basis. Take the time to experiment with your sail settings to learn what each setting does to the performance of your boat. Also take the time to look carefully at how the leaders in your fleet set their sails. The beauty of sailing is that there are a number of combinations of sail settings that will provide you with good VMG (Velocity made good).
 
Also remember that making a change to one setting could affect another. For example, changing the backstay tension effects the leech of your mainsail, but it will also alter the slot between jib and main. Watch carefully the alterations to your rig as you make changes to various parts, and make sure you make the corresponding correction to the unintended change.
Match mainsail luff curve to mast curve.

The leading edge of a mainsail is not straight in most cases. There will usually be a gentle curve from head to tack. A good starting point is to ensure that the curve of the luff of the sail matches the mast bend.

Many skippers like to build their rigs with a small amount of forward pre-bend in the top 40% to 50% of the mast. The backstay is then used to pull this pre-bend out, increasing the amount of jib luff tension that is able to be generated.
 
The photos on the left top and bottom show a mast curve which is less than the luff curve of the sail. You can see a knuckle along the leading edge of the sail which will disturb wind flow.
 
The right pair of photos show a mast curve which is too great for the luff curve of the sail. The sail shows creases at about the height of the numbers.
 
The centre pair of photos shows a good match between mast curve and sail luff curve.
Is your mast vertical?
 

In the quiet of your home or shed, it is possible to rig the boat and measure the distance from the hounds to the deck line on each side of the boat. However, at sailing, this isn't always possible.

 

A simple way to judge whether your mast is vertical, is to look at the lay off of the leech of your mainsail when the sail is sheeted fully out. Compare the lay off of the sail on port gybe to that on the starboard gybe. If the leech lays off more on one side than the other - then the mast is leaning towards the side where the sail lay off is greater.


In the example, in the top photos, the leech lays off more on the right (starboard) side than the left. The mast is laying slightly towards the right. By loosening the right (starboard) shroud, and tightening the left (port) shroud, the mast becomes more central, and the lay-off of the leeches are more equal, indicating that the mast is more vertical.

Set your vang tension to adjust downwind leech shape.

 

To set the vang tension, allow your mainsail to sheet right out into the position it will be when you are sailing downwind.

 

Tighten the vang until the leech of your sail is fairly straight in the lower two thirds. There should be some twist in the upper third of the mainsail.

 

The picture on the left shows the leech falling away too much. The wind will spill when sailing downwind and the sail will not provide sufficient drive.

 

The picture on the right shows a leech which is about right.

Adjust the main leech for upwind sailing

 

After setting the vang for downwind, sheet the mainsail in to the close-hauled position. Initially, you will find that the leech is too tight for upwind.

 

To make adjustments to the leech for upwind, try to adjust only the backstay and mast ram. These two adjustments will only affect the leech in the close hauled position.

 

if you find the leech is still too tight, there may be a need to offset the gooseneck, by placing a thin packer under the bottom screws. Normally, about 3 wraps of sticky back sail cloth is sufficient to offset the gooseneck and correct the mainsail leech.

The picture on the left is typical of the leech shape for upwind which you will see after setting the vang for downwind. The shape you are aiming for is shown on the right - straight in the lower two thirds with some twist in the upper third.

Jib slot

 

The slot between the jib and mainsail is very critical. if the slot is too closed, the mainsail will backwind early interfering with normal airflow. Conversely, if the slot is too open, there will be spilling of air, and consequently, less power generated through the sails

 

The left photo shows a slot which is too closed, and the right photo shows one which is too open. The centre image is about right.

Set the foot camber on your sails

 

The foot of both the mainsail and jib can be set according to the conditions you will be sailing in. Generally, the foot camber is greater when sailing in waves or choppy water, and flatter when sailing in flat water.

 

As a starting point, for flat water or in very small chop, the A rig should have about 25mm of camber in the mainsail and about 30mm in the jib

 

The B rig will have a similar setting in flat water, up to about 35mm in chop. The C rig will vary from 15 to 20mm in the main and 25mm in the jib.

Sheeting Position:
As a general guide, the mainsail is sheeted closer to the mid-line of the hull in lighter conditions and in flat water. As the wind increases towards the top end of the range for the rig, you will want to sheet the mainsail further from the mid-line to reduce the healing moment, and increase forward motion.


The jib is sheeted approximately 55mm to 65mm from the midline of the hull for the A rig, and slightly further out for the B and C rigs.

The mainsail will be sheeted about 15 to 20mm away from the centreline of the hull.

You can use the relative sheeting position of the two sails to help balance the boat as well. A boat with weather helm might need the main to be sheeted slightly further out, or the jib to be sheeted a bit closer.