Today we tow-tested K2 to see how well the boat performs at very high speeds. Specifically, we wanted to determine the cavitation point for our foils. We are using a conventional section for the foils, which means that our foils are designed to operate at speeds at which they do not cavitate. The cavitation point of a foil is the speed at which the water passing over it turns to vapor; cavitation on our foils would prevent them from providing lift and the hulls would drop into the water. Most foils utilize a conventional section, but certain high-speed vessels utilize a caveating section, which allows them to continue to provide lift, even while cavitating. We experimented with cavitating foils on K1–the last iteration of that platform had a cavitating section on one keelfoil and a conventional section on the other keelfoil–but we found the cavitating section to have too much drag at low speeds. On K2, we have not yet hit a speed at which our foils cavitate, but we have also only sailed below 33 knots. Today, we towed the boat up to 41 knots, and still did not observe any cavitation, which is great. The Protector was unable to tow above this speed, with five people on the Protector and one person on K2.
Another goal of high-speed towing was to determine what speed it took to get K2 on the foils and to keep it on the foils, and to gather associated load information. We attached the SpinLock load cell to the tow line at the boat attachment point. With three guys (Joe, Greg, Alf) on K2, we completely foiled (T-foil and J-foils up) at 19 knots, and with only one guy (Joe) on K2, we completely foiled at 14 knots. With a crew of three, our top speed was 38 knots, with a load of about 200 kgf. With a crew of one, our top speed was 41 knots, with a load of about 220 kgf. Towing the boat from the Protector does not mimic kite towing, but it is still useful to us to know approximately what loads we need to achieve foiling and to maintain foiling, and to know how the load increases as the speed increases. A full data writeup from Jamie will follow.
Finally, we debuted a new camera mount, made from attaching our A-frame kite launch mast at an angle behind the helm. We were able to achieve some great new camera angles this way, and will make some alterations before using it on a kite test. Overall, it was a fruitful test on a beautiful evening.
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