They gave the SailRocket a proper launch in Walvis Bay…
We attached a long towline and proceeded to slowly pull VSR2 away from the land. Once out I straddled the hull, made my way back to the main foil and lowered it down to the locked position. VSR2 doesn’t track very well without the foil down and the rudder is next to useless at low speed. Depth paranoia struck instantly…
Once away from the shore I lowered the main foil once more and we began towing. The nose float immediately went under. I know not to get alarmed until we fully understand what is happening, but this was surprising as these floats have huge amounts of volume. Each float should be capable of supporting the whole boat.
We were towing VSR2 by the nose and after another short trial we set up a different bridle system. The main fuselage needs to travel along at a 20 degree angle, as it is cocked sideways rather than in fore and aft alignment, so that it points into the ‘apparent’ wind at high speed and greatly reduces the aerodynamic drag on the boat.
We adjusted the bridle so that the towing point was about 10-12 feet inboard and set off again. Annoyingly, the nose was still going down and even with the 60 hp engine on full throttle, we couldn’t get the boat to ‘pop’ up out of the water.
I worked the rudder through its range to see how much response I could get. I had to make sure that it wasn’t fully stalled and off to one side. If it was then it was completely ineffective and just creating drag. When I turned the steering more to the left, the nose would turn more to the right, due to the flow becoming re-attached. Although the angle was decreasing, the effectiveness was increasing. (Note that the rudder is a wedge shaped high-speed section with a profile more like an axe head than a teardrop). It was still effective at low speed, but only in a very narrow range. Once I got a feel for this and we began a turn to the left, the bow popped up, the drag decreased, the Rib was able to accelerate… and we were off! We punched a big hole through the mythical ten-knot barrier and up to the lofty heights of around 16;)
Wing test take 1 + 2
There is so much to be seen and learnt about this new wing!
The first day’s land-trials with the wing in a decent breeze – around 17-22 knots, went well. We started by seeing how it handled during the wing-raising process. We set it up in the rigging yard and raised the middle section of the wing, which is the section that should be free to fully rotate through 360 degrees if necessary.
Normally, we pulled the previous boat’s wing up a 6:1 purchase via the strut and a Harken track, but as the new wing is tail heavy, it hung ‘at rest’ with its back down. In this position the wing generated substantial lift all by itself! By generating lift, instead of having to haul the wing up, we simply eased it up by releasing the shrouds in a nice controlled manner! As the wing goes vertical, the imbalance becomes less pronounced and the wing naturally feathers more… a revelation albeit calculated.
Once the wing was up we could just let it go. It would sit in the gusty breeze perfectly happily with relatively little residual force. We spun the boat around underneath it to simulate a few angles of the rig to the platform. We became aware of a few ‘no-go’ areas where we simply can’t power the rig up as it will put forces well outside the shroud base which will lead to massive loads in the wing strut. As long as we respect these then we should be OK.
We also tried swinging the beam fore and aft with the rig up and learned that we need to increase the range to around 2.5 meters from the current 1.5. This will be how we steer the boat from standstill when the little rudder is ineffective. It will be very important to get this whole system safe and reliable in order to have full control, at all times, in winds up to 30 knots.
When it came time to drop the wing, we had to pull it down! The wing is tail-heavy in its current form, but we can balance this by putting a pole out in front with counter weights on it. We might have to do this to help make the wing feather more. We will see how it behaves as we begin adding further elements. So far it doesn’t seem necessary.
We are looking at trying to get the floats to release from the water and plane on the surface with less effort (decrease the ‘hump’ drag). It is only when the air gets to the ‘step’ that the hull releases and the suction is broken. At low speed, this ‘step’ is too deep and the air can’t get to it. We are going to try adding a small second step on the aft surface to try and break this suction cycle. It is an easy experiment that may have a big effect on how well the boat accelerates from stand still. The text is Paul Larson’s, edited by Lia Ditton. Images courtesy of Helena Davelid/VESTAS SailRocket. Ben Quemener is on the case today!