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Trim yout KONA OD Sail - english.konafinland.com

Trim your KONA One Design Sail

The KONA One Design sail is quite an unusual design, it has very little mast curve, and accordingly very little tension.

The KONA OD sail requires a lot of batten tension according to the experts (sail designer). By adding batten tension the skin tension increases very significantly, and the feeling of the sail changes from a "soft freestyle sail feel" to a "stiffish fixed camber sail that rotates with a bang"

A lot of batten tension produces a lot of belly. It seems as when the skin tension, and the general tension of the sail, increases then the twist starts to work as designed. The mid leach does not bulge anymore, instead the top twists off properly in the gusts.

The high batten tension compensates for the straight mast curve and helps to firm up the leach of the sail. In higher winds more downhaul will open the head as on any freeride sail.

One expert opinion:

Batten tuning is very impotant in most sails and even more important in a sail like the KONA One Design and the Aerotech Zenith. It will not hurt the sail to leave tension on the battens. There is a lot more strain on the race sail pockets as the battens are much stiffer and it takes more force to put tension on them. You will get some stretch in the sail but this will not hurt durability or performance but you will have to add more tension over time. It would probably be slightly better for the sail if the batten tension was released but I do not think it is a big deal.
My own observations:
Overtensioning the battens of the KONA OD rig really transforms the rig. It feels in low wind like a camber sail, it drives with the slightest breeze. When tacking, or gybing, the sail also feels like a camberd sail. It requires a firm pull to rotate, and then does it with a real bang (in light winds you may need to help the rotation by hand).

With normal batten tension the sail folds in the middle (battens 3 and 4 from the top), and releases pressure at the batten above the boom. This also leads to severe leach flutter. By overtensioning the battens the mid leach is tightened and the sail twists off from the top. At least in marginal planing winds there are no signs of leach flutter with this setup.

With the tensioned mid leach the OD-sail has quite a lot of planning power. It now reacts well to pumping, and does not release the pressure anymore. With normal batten tension pumping did not seem to help at all, the sail folded and nothing happened. With more tension the board accellerated with every pump, just as it is supposed to do. When planing the tighter mid leach allowed the sail to twist beautifully, even if there was no visible loose leach at the beach.

This can be seen from pictures  where a sail with normal batten tension opens at mid leach. A picture of the OD sail with high batten tension would show a beautifully twisted sail, just as expected.

There was still a problem with a poorly defined Center Of Effort when sailing in light and gusty winds. In every gust the COE would instantly move back, forcing the mast to swing forward and into the wind. Having the hands close to each other was thus difficult as it required the back hand to be moved back on the boom very swiftly to counteract gusts. Maybe someone fels that the sail is reactive this way, but I did just find it annoying. The good news was that once the COE had moved back a little it seemed to stay there as the top started to twist off. That is, the sail seemed to behave very well (stable) at least in marginal planing conditions.

Check out these pictures and tips to learn more.

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