Today we took the 50 sqm kite out for the first time with the new, stiffer battens at the wing tips. The kite was still deforming a bit toward the middle, but the stiffer battens helped it hold shape near the flying lines. We’ve also been more successful at avoiding kite deformation by steering the boat to maintain optimal kite shape. With four people on board, we hit a top speed of 33.5 knots, and we were able to go up to three times the wind speed, clearing 30 knots in 10 knots of wind. It also helped to have Jacques Vincent, the co-skipper on the Hydroptere, take the helm for a bit. Near the end of the test, Greg hopped […more]
November 2012 Archive
Due to stormy conditions, we started late today and brought only a 25 sqm kite, but we were lucky and missed the rain. The wind was strong, and for the first time we successfully executed multiple foiling uploop jibes. An uploop jibe facilitates foiling through the turn by pulling up on the boat when it’s most likely to drop off the foils and then powering up just after the turn, when the boat needs an extra boost of speed to keep going. However, uploop jibes are difficult because they require fast maneuvering of the kite and lots of wind in order to keep the kite from stalling above the boat and falling behind the boat. If the boat passes in […more]
Today we towed K2 with the Protector again. This time, we attached the load cells and the tow rope to the kite chair, to more closely approximate the kite force on the boat. After the tow test, we put up the 50 sqm red and blue kite, and we hit a new top speed with the boat, 36.3 knots! We sailed exclusively in the protected area off Alameda Point. Our data logger confirms that we exceeded 35 knots multiple times. Our previous top speed with this boat and kite was 32.5 knots. Note: Speedpuck said 37 knots, Jamie’s data logger said 36.3, which is probably more accurate; our previous top speed relied on Speedpuck’s reading. Screenshot from KAIView is attached.
The tow test on Wed Nov 14 provided some insight into how much force is needed to pull our kiteboat at a range of speeds. By measuring the tension of the tow line and plotting it against the boat speed, we can infer the approximate force that a kite would need to generate to pull the boat at those speeds. The first attached plot shows only the tests with a crew of three, for which the maximum sustainted speed was 38 knots. The second plot shows the towing power, calculated as the product of the force and speed. The polynomial fit (red and green lines) may be helpful to understand the density and trend of the collected data, but should […more]
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 […more]
Today we headed out to test several new components on K2. We tested the new motorized winch for the first time, and we used a new car (which houses pulleys and load cell) under the seat, which was an upgrade from the former aluminum car. We did not plug in the load cell but structurally tested the system. The new winch worked excellently. Dudu flew over in his helicopter, and Gino Morrelli and Bruce Sutphen, visiting boat designers, joined us on the kiteboat and Protector. The kite seemed to be deflating the entire time, perhaps as a result of the inflator accidentally turning off during the test. Despite this behavior, it was a great test. We hit our fastest K2 speed of all […more]