Well I have now had a chance to digest yesterday’s mammoth day. Here are the results.
It was indeed a great wind day. Almost the best that this location can possibly offer. These days are few and far between and although there have probably been many over the years, there has not been one during the Americas cup regatta (last week of March) since the current record was set in 1999. So with over 100 expectant land sailors watching the pressure was on to perform. The wind was coming out of the SSW and averaging between 25 – 32, but gusting to 40.
Ivanpah Wind 22-03-2009
Here is the days wind graph, dark blue is the average and purple is the peak gust.
This was the first time that the Greenbird, in its new configuration had run at speed, so it was going to be interesting. I started sailing at 09:12 and finished for the day at 5:30pm, after covering 172 miles (277km). During the day we did many pit stops, changing wheels, compounds, tyre pressures and ballast distribution to eke out more speed and tune the vehicle for the conditions of the day.
The final top speed was 107.12 Mph. A frustrating 9 mph short of the record speed.
Ivanpah Track Dist 22-03-20009
Here is the track from the days sailing. You can see I tried to use every available space and try every angle to aid acceleration. In fact I really gave it everything I had to try and get it past the illusive record speed. You can see here by the measurement tool, that the venue only really provides 1.8 miles, for the entire run, including stopping.
It was initially disappointing that the craft was not going much faster in these sort of winds, but after much testing and understanding, the results are very encouraging. The problem here is simply the length of run we are able to use. All the top speeds were in the last seconds of the run, with the craft still accelerating hard, but I had to de-power hard to stop before the end of the lake. I will graph the acceleration curves for you later, but the yacht was accelerating at 0.6 mph/sec at 107 mph, meaning about another 20 – 30 seconds required to hit 120, meaning we needed another 1000m to reach top speed. (Top speed is when acceleration has reached zero, demonstrating we are some way off the vehicles top speed).
But, the current record was set here, was it a faster craft? Not necessarily. It had more wing area and a wing shape that performed better at slower speeds, so was able to accelerate faster. But, it is a trade off, fast acceleration at slow speeds (also like Windjet Mk 2) means sacrificing top speed performance, due to being overpowered and a poor induced drag characteristics at top speed. We spent a lot of time optimising the Greenbird wing for the precise record speed, no slower. this should yield the ultimate top speed, which is what we are searching for after all. However, this means acceleration is slower, and we need possibly twice the acceleration distance as the Iron Duck, but the ultimate speed should be higher, and this was exactly what we experienced, short of finding the top speed! There are high lift devices you can add (flaps, etc) to speed up acceleration, but not without some complexity and as we designed this craft for Australia, where we had up to 10 straight miles, I did not bother to add additional weight or expense to the wing.
So where now? Well we will look at the numbers again to see if we can improve the bottom end speed with the same or a different wing, without compromising top speed. Otherwise, we will need a different venue. There is obviously always Australia, but there are also other alternatives here in North America, which we are researching. Realistically however, we are unlikely to break the record here at Ivanpah unless we get a stronger, or more steady wind, from a slightly kinder direction, which is a big ask and may take another 10 years of waiting!
The very good outcome is that the vehicle behaved perfectly, despite taking a pounding, no failures, no problems, and excellent handling. This is immensely satisfying when it is a craft you have engineered and built yourself. Performance is also now proven (matches performance predictions to this point) so I am more confident than ever that we will get the record, but it is no mean feat. The closer I get to the speed, the more respect I have for the current record holders. They really did set the bar very high and it is certainly no walk in the park.
The really unfortunate side of the day is that we did not get it on proper film. Simon from BHP and our film crew were suppose to have been here, but when their plane was 1 hour out of Gatwick, it had a critical engine failure, meaning it had to return to Gatwick. ( hours of waiting for a new plane means they will arrive in Vegas this morning as the wind is just calming down). Very frustrating for everyone, but hopefully we will get a chance for more action later in the week. We did get some amateur footage from bystanders, which I will post shortly when I have had a chance to view and edit it, but it won’t be a patch on Simon’s quality I am afraid.
So there we have it, close but no cigar. We will hang out here for another week or so, just in-case the wind does get even better, which it may. The jet stream is being kind to us for once and pushing storm after storm down from Alaska into the right area. There is currently wind forecast for Thursday and possibly next Monday.
Greenbird in motion
Greenbird at speed