On Water Setup and Tuning

What should my sails look like?

BEFORE you even go sailing its important that you have the boat set up and calibrated correctly so you can make the appropriate changes on the water. If you haven’t done that visit ON SHORE  to find out what control range you need and how to calibrate a 5O5

                MAINSAIL SETUP.

Make sure the mast bends to suit the luff round in the mainsail you are using.

If you use a Tuning Grid, you have the same mast and sails and are using the same calibration methodology as stipulated in the Tuning Grid, you should find the mast bends in a manner that suits the mainsail. Someone else has done a lot of the hard work for you. However every boat layout, mast and sail can be slightly different so it is worthwhile checking the Prebend in your boat is correct for the mainsail used.

If you don’t have exactly the same equipment as that used to develop one of the standard Tuning Grids you definitely need to make sure your mast is bending to suit the luff round cut into the sail you are using.

Right click picture to see larger version

Hold finger on photo to select larger view

Mast Prebend and Luff curve in the mainsail should match. Adjust spreaders, shroud bases or mast step location to get the correct prebend amount.

We induce Prebend into our mast when we pull rig tension on and load the spreaders. The mast is ‘pre bent’ because it is forced into a bend even before we put a sail up or go sailing.

Depending on the spreader configuration relative to where the shroud bases are, the mast will generally bend when rig tension is applied. The amount of mast bend (the offset from a straight line) should match the luff round in the sail you use (see photo).

The sail maker will generally have incorporated the luff round in the sail to suit a particular mast configured a particular way. In its simplest form, the prebend is measured as the offset between the back of the mast and a straight line at the spreaders. ( diagram and photo.  some video with a voice over explanation)

A Tuning Grid should tell you what mast configuration (particularly spreader length and angle) you need to get the design prebend for the sail you are using. If it isn’t shown on your tuning grid you may be able to ask the sailmaker or one of the fast sailors that use the same sail and mast. Otherwise you can measure the sail luff round at the height of the spreaders yourself (photo or diagram). Then with the rig set up properly (spreaders, mast step position, side stay position and rig tension snugged up reasonably tight), you can also measure the prebend at the spreaders. If everything is set up identically to the tuning grid you should find the prebend and mainsail luff round match. However each boat can be slightly different so you may need to adjust your spreaders or shroud base slightly to get the correct prebend measurement to suit the sail you are using.

Now when you put the mainsail on the mast the sail should set just as the sail maker intended. When you go sailing and pull some vang and or mainsheet (which will also now bend the mast above the hounds) you should have a sail that can be set perfectly.

In summary, for best results, the mast should bend when you go sailing to perfectly match the luff round the sailmaker designed into the sail.

When Prebend matches the luff round in the Mainsail the shape built into the main body of the sail (seam shape) and the depth that the sailmaker intended should work as designed.

This diagram thanks to P&B Sails, depicts creases  that can occur with too much low down mast bend. See Where It All Goes Wrong for more.  If the mast does not bend as expected the sail can be pulled out of shape in one area or another and won’t perform as it should. Particularly as you start to depower it.

Prebend is normally measured and calibrated with the mast in the most upright rake position. This should give you a fully powered mainsail ready for the lighter wind range. From here you will make adjustments as wind conditions change which are discussed in How Do I change Gears.


The jib is very easy to set up wrong. It is also often claimed to be the most important sail on the boat. It contributes, for better or worse, more to a boat’s power and performance than one might expect given its relative size compared to the mainsail. The jib doesn’t just create power from its own shape. It feeds air around the leeward side of the mainsail which significantly increases the power that the two sails would generate on their own.

The ‘slot’ between Mainsail and Jib can be as important as the setup of each individual sail. So when a jib is being set up its important to consider both the jib shape and the slot between it and the mainsail.

Tell tales on the jib are the only way to be sure a jib is set up properly. As a minimum, there needs to be 3 on the luff and one on the upper leach where it can be seen through a window in the mainsail.

Tell tales are essential to sheet a Jib properly. You need at least one tell tale on the upper leach and 3 on the luff as seen in this photo.

Unlike a mainsail, where the main sheet has less effect on sail shape[1], small changes in jib sheet tension make big differences in sail shape and therefore performance.

Jib sheet tension and the position of the Barber Hauler[2] need to be used together to get the correct jib shape. Change one and you generally need to change the other.

To initially set up the jib on the water,

  • The in/out Barber Hauler position can be set simply by matching how far outboard it is with how far off the centre line the boom is. Or just use the measurement provided in a Tuning Guide.
  • The fore/aft sheeting angle can only really be done properly on the water. With the boat sailing properly on the wind, the objective is to have the jib leach tell-tale on the verge of stalling or actually stalling occasionally AND the 3 luff tell-tales all flowing AND all 3 luff tell-tales breaking together when you pinch the boat up into the wind (luff).

Jib Barber Hauler lead. Moves in and out to adjust how far outboard the jib is sheeted.

Jib Barber Hauler lead can be pulled down to sheet further forward.

Barber Hauler in/out position.

This is typically measured from the centre line of the boat and the measurement for different wind conditions can usually be obtained from one of the Tuning Grids. However it isn’t rocket science. When conditions are such that you will have the boom all the way in, the jib lead should also be all the way in. About 47mm from the centreline[3].  As wind increases and the boom needs to be sheeted further outboard, set the jib lead proportionally further outboard as well.

Barber Hauler For/Aft Position[4]

Now you need to set the fore/aft position of the Barber Hauler so the angle that the jib sheet pulls on the jib is correct. This is generally when all the jib tell-tales are streaming. You should have one on the upper leach and 3 up the jib luff (see photo). To do this you need to be sailing properly upwind. Sheet the jib on until the leach tell-tale stops streaming and then ease just enough to make it stream.

Now check the 3 luff tell-tales are streaming and they all break at the same time when the boat is luffed. Steer the boat up (pinch) while watching the tell tales to check they all break together. It is OK if the top one breaks marginally earlier[5] but don’t have settings where the top tell-tale breaks after the lower ones.

Keep an eye on the tell- tales regularly while racing. If the leach tell tale is stalling too often you may have to ease the jib sheet just a tiny amount. If the top luff tell tale is breaking before the lower ones, the jib is too open and you may need to sheet on harder (unless you are overpowered). If you cant find a jib sheet tension that allows both the leach tell-tale and the top luff tell-tale to stream properly you will likely need to adjust the Barber Hauler.

If the Barber Hauler lead block is further down or forward, the jib sheet will pull relatively less along the foot and more down the leach which will close the leach (less twist) earlier as you sheet on. If the lead is moved back or up, the sheet will pull more along the foot and less down the leach which will cause the leach to open up more (more twist).

5O5 set up for high winds with plenty of twist in both sails to depower.

Minimal leach twist for light under powered conditions.

Leach twist needs to be same in both sails so slot between Main and Jib is parallel.

Two 5O5’s with maximum leach twist to ride out a squall

 Foot notes:

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[1] Up wind mainsheet tension can be used to flatten a sail and tighten the leach. In very light winds mainsheet tension is very important in controlling the twist.

[2] The movable block that the jib sheet is lead through which controls how far outboard the jib sheets and the angle the jib sheet pulls on the jib. See link for more and photo

[3] Except in very light conditions when moving it outboard a little improves air flow through between main and jib.

[4] Some boats are rigged so the barber hauler block is moved up and down instead of fore and aft. The change in sheeting angle can be achieved either way.

[5] In very overpowered conditions a lot of jib twist is often used. The top tell tale-would break well before the others in these conditions.


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