1. Make sure the control lines in your boat can give you the full required range. Particularly rake and jib barber hauler.link
  2. Calibrate all the control lines so you know where you are in the range and so you can replicate settings. If you are using a tuning grid make sure you are using the same sails and mast and the boat is configured and calibrated as specified in the grid. link
  3.  If you are not using a standard set up, check that the pre-bend in your mast is the same as the luff round in the mainsail. Even if you are using a grid you should check that the settings are giving you the required pre-bend.link
  4. Whether using a Tuning Grid or not adjust the rake through the full range and make sure all the settings are calibrated so you know what each setting needs to be to keep the pre-bend fairly constant through the rake range.link
  5. Go sailing. Set the rake for the conditions (from experience or using a Tuning Grid). This generally does not need to be super accurate. Don’t change it too often.
  6. Set all the other settings to the position that corresponds to the rake you have set.
  7. Ensure Jib is sheeted outboard to match proportionally how far off centre the boom will be.
  8. Ensure jib sheeting angle and tension is correct so jib depth and twist match the mainsail set up.
  9. From here, if overpowered flatten the mainsail. If under-powered make it slightly deeper. Do this by adjusting shroud tension, Cunningham, vang and jib sheet tension.

Broadly, in all conditions you want to keep the mast pre-bend suiting the mainsail. The controls at your disposal while sailing should allow you to change the shape slightly around this ‘neutral’ position,  Flatter or fuller. However if the mast is allowed to bend too much or in the wrong places the mainsail will likely be distorting beyond its design range and become inefficient, unstable and difficult to control.

The objective is to reduce power in the top of the sails first, leaving the bottom sections to keep working. (So bend the top of the mast first). Similarly when it is very windy we are happy for the front of the mainsail to collapse but still have the back half (the leach) working. Otherwise the whole sail flogs and the boat becomes unbalanced and will create a lot of drag.

See this picture of Olympian & UK Olympic coach Penny and Russ Clark sailing a 5O5 in very windy conditions. The boat is very overpowered but the leach of the bottom of the main is still working to provide balance and the boat remains stable.

The top of the mainsail and the front part of the mainsail are clearly not doing anything.

VANG. In lighter conditions, before the boat becomes overpowered, most if not all of the mainsail leach twist is controlled by mainsheet load. The Vang is typically not loaded. (see separate article for end boom sheeting boats).

So before we ease the boom to de-power, the Vang needs to be pulled on to take over controlling leach twist.

Ideally you will have a mark on the Vang system so you know where to pull it to so its just right when you ease the main in the gusts.

When the gust eases and the main is pulled back in, its important to ease the Vang again to fully power the main back up.

You should also have a mark on your mainsheet so you can instantly pull it back to the right spot without having to look around too much. Leaving the Vang on in a lull is likely to cause the mast to bend too much up high which reduces overall power when you don’t need to and will t