This is a basic guide to 49er tuning.

First start with what we call a base setting.

Base Setting

Shrouds 28 - 29

Caps 14 - 15

Lower bend 10mm


Tensions are mesured using the loose spring gauge

To measure lower bend. Firstly file a small grove in the front point of the lower spreader bracket.
Take the spinnaker or jib halyard, pull it tight, move it in to the mast so that it sits in the grove in the spreader bracket.
Move it in towards the mast untill it touches the point at which the mast is bent the most.
Measure the distance between the inside face of the halyard and the mast, do this level with the boom goose neck fitting.
Effectivly you are creating a tangent at the point of maximum bend.



Overview

Start with getting the above setting, this will take some fiddling with various combinations of shroud. Cap and lowers.


As the wind gets up progressively move down the shrouds and caps. These are done in equal
proportions, so that if you are using turnbuckels just adjust the bottel screw.    The smallest increment of adjustment with chain plates is 4mm, this equates to 4 complete turns of the turnbuckle.

As a guide it is time to tighnten the rig ( going down ) when the windward shroud begins to go slack. Or you feel overpowered.
Fill in the tensions for each setting your self, as these will vary a bit from boat to boat.


Other settings

Jib tack - Bottom of jib level with top of forestay swage bring this down as you become overpowered.


Jib Track - use track 4. 5 when really overpowered.

Centerboard Keep it down untill overpowered then progressively raise to control power.

There is a sort of process or order of depowering and the reverse is true to power up. As the wind increases and the boat begins to become overpowered, start with more rig tension then jib tack down, then board up, then track out.

More on the subject of power control can be found here.