I made a little video on how to improve the windrange of most wave sails. For example the older Witchcraft sails up to 2026 but it will work even better on sails of other brands that are cut flat. This is done by giving the middle 2 or 3 battens a bit more taper by sanding the batten tips down to 1.6mm. You should not touch the top batten. The foot batten can be done a bit as well but 1.8mm is enough. This has given a noticable increase in windrange of both the Karma and Slayer.
However, for sails that are cut flat or nearly flat (meaning they are flat or nearly flat when lying down, which is the case with most wave sails), this will increase the wind range even more. Flat sails need more windpower to bend the battens into shape to throw profile and depend on batten taper alone for their profile stability.
With more batten taper, you will need less wind to throw the profile and at the top end range, the sail will have more profile stability. It will be smoother and easier to find the angle of attack. Also batten rotation becomes softer when flipping the sail.
We found that most battens don´t go thinner than 2m 2,5 or even 2.8mm. To illustrate how effective that is: The stiffness of a profile relates to the 3rd exponent of the thickness, so just this little bit makes a big difference. 1.6mm is already twice as flexible than 2mm (1.6³= 4.096 and 2³= 8) Meaning that you will need half the wind strength to throw the same profile depth, which is right when you need it most. 1.6mm is more than 3 times as easy to bend than 2.5mm (2.5³= 15.6).
By pulling out a batten you can check how it bends. Compare this to the image in the video. Like this you can judge whether it should have more taper. Most of the time it will. You can sand the batten tips down to 1.6mm (without shrinking tube). This is still enough to easily support the batten tension. Before sanding, remove the plastic tip and the shrinking tube. Then, on a flat surface, sand the tims gradually thinner with a sanding block, on both sides of the batten. Follow the original taper. The length of the taper can also become a bit longer. Do one batten first and compare this with another batten. Be careful with the fine sharp glass splinters. When you think you have the right taper, you can either spray the sanded part with spray paint or put electrical tape length wise, over the plastic tip and back up the other side. You can rig the sail and see how it sets. If you have an old sail with good battens, you can also try it with them. Like this you can always compare with the original battens. I have done this on sails of various brands, for example if they had broken battens and I needed to custom shape new battens from a straight round rod. Afterwards the customers came back and said their sail worked better. After explaining, they asked to do their other sails as well. Let us know in the comments if you did and how did it work out or if you have any questions.
