I have the Sword 2 also, and my motivation to work on the foil was mainly due to the singing/whistling noises it generated from Day 1, straight out of the box. After much frustration my research (talking/emailing/phoning people) only got me so far. Even the people that told me their Sword 2 was silent and fast couldn't (or wouldn't) tell me exactly how they did it. Trial and error got me the rest of the way. At the very least, I can tell you what worked for me. I have developed my own theories during this process, which may be completely wrong, but at least I am happy with the results.
As of now, my Sword 2 is 100% silent on all points of sail, and rides smoother and more stable than ever.
1. Disassemble your foil and follow George's instructions for Bondo glazing/spot putty in this video: . Apply to mast and both wings. I did not apply the Bondo to my fuselage except for a couple scratched spots. There are more than one Bondo products that can be used, but you want the 1-part product here: https://www.amazon.com/gp/product/B0002 ... UTF8&psc=1
2. Wet sand. I wet-sanded the Bondo off with 400 grit to start. I started sanding within 30 minutes of applying the Bondo (it dries FAST), and all the excess Bondo comes off quickly. I did all sanding by hand, no sanding block. When you sand, sand at 45 degrees to the edges of your wing & mast edges (trailing, leading, etc.). I sanded each surface in both directions, first 45 degrees one way, then the other way. Make a few passes first with 400grit, then work your way to higher grits, making several passes up and down the foil with each grit #. I have experimented with several grits of sandpaper. At first, I sanded every surface all the way to 1200. I rode the foil for several months like this, but there was always a noticeable humming noise on starboard tacks, when riding slow. I never figured out why.
I recently went at it again and re-Bondo'ed the entire foil (filling in some newer scratches along the way), and followed the grit numbers from one of Gunnar's videos (Levitaz review, maybe?) just to see what would happen. I sanded the wings to 600 grit all over (first 400, then to 600). On the mast, I sanded the trailing edge (back half of mast) to 600. I sanded the leading edge (front half) of the mast to 1200 grit. All sanding at 45 degrees to the edges. The foil is now completely silent, and feels more stable again.
3. Trailing Edge treatment. George has another video where he says to sand the trailing edges of mast and wings "square" with a sanding block in order to eliminate noise from your foil. I tried this numerous times over several months. It made it WORSE. Way worse. I may be wrong, but I concluded that for whatever reason, maybe because it is so thin, the mast profile of the Sword 2 is not compatible with this square trailing edge geometry. My trailing edges are now all still relatively sharp, and I have no noise. I think the key was sanding by hand. Perhaps the variations in pressure as you sand across the trailing edge create imperfections in the surface that break up the flow of water, eliminating the resonance of the material that creates the singing noises. Again, only my own theory.
4. Check that your wings are at 90 degrees to your fuselage. In spite of the high quality of production on these foils, you can still screw your rear stabilizer on at an angle slightly off from 90 degrees. I made a template on a big piece of paper using a T-square that I set my assembled foil on top of. The lines on the paper show me straight lines for my fuselage, and straight lines at 90 degrees for my my rear stab. I check it every couple/few sessions and I find that even with snug screws, the wing can move or get bumped out of place. When the wing is not at 90 degrees, the foil may generate noise, and it can also be less stable.
This is what worked for me. I am not a racer but, like you, I enjoy pushing the gear and myself and going fast from time to time. A different grit on the foil might make it a couple knots faster, but I am not sure I can tell with my experience level.
For me, the main thing is successfully eliminating the horrible noise, and knowing that I can "tune up" my foil periodically when it feels a little wonky.