Sail-World.com : Sailrocket 2 - Big day with top end conditions
Sailrocket 2 - Big day with top end conditions
The Vestas Sailrocket 2 crew are in Namibia attempting to break the World Sailing Speed record. They are now into their official WSSR record attempt time period.
Pilot Paul Larsen:
(Wed, 7 Dec 11 21:53)
What a big day. I don't think we have ever done five runs in a day let alone in such top end conditions.
We went out there and went for it today. There were things that I needed to see. The conditions were, of course, just a little too much. The wind was gusting to 34 knots but I couldn't afford to procrastinate. Throughout the day I had come to realise that we are wasting our time down around 50 knots. The whole Vestas Sailrocket 2 program is based around making ventilated foils work so that we can hit speeds over 60 knots. Small incremental gains around 50 knots is not what we are about now. I had a job list to work through, a tough boat and a solid team who are comfortable handling her in strong conditions. It was time to push.
All runs were done with the ventilated/wedge foil
Run 1: Day still building so still a bit light, one person onboard, Easy run with a peak speed of only 44.3 knots. Nothing remarkable. No vibrations or unusual handling. Did a weave down the course with the rudder simply to see how the boat behaves and if any play in the system misbehaves. It didn't. We can reference this change from positive to negative loading later.
Run 2: Day building strong, 25-30 knots. Two people on board (Helena's first proper run in the boat). Still a bit difficult to start with two people but nevertheless a good run. Peak speed 48.87 knots. Nothing remarkable again. No vibrations or unusual handling. Pod flying towards end.
Run 3: Wind 25-33 knots. One person onboard. Decided to try to max out the boat in tope end conditions. If it was going to ventilate... it would do it now. It didn't. This was this foils last chance. We maxed out at 50.8 knots.
This was not enough. Still no signs of the evil vibration. We should in theory be doing over 70 knots in these winds. Time to go under the knife.
Run 4: Wind 25-33 knots. One person onboard. water rough. 15 cm removed off the tip of the foil. I was expecting to see ventilation or at least the return of the vibration to show we were headed in that direction. I dipped the wing extension in a wave trough during the launch and did some minor damage. Peformance wise it was still fully functional. After a quick over the shoulder assessment I went for it. The start-up was noticeably less 'crisp' but VSR2 still hooked in and took off. She felt a bit more lively. As I beared away onto the course she did a big weave that took a fair bit of rudder to correct. This could be the foil switching between attached and ventilated flow. It felt like there were moments of 'release' in there and even the run itself felt faster.
It was rough though and this always adds drama and a sense of speed. It felt better although the peak speed was almost the same at 50.52 knots. The average was lower at only 46.02 knots. Oddly no vibration or sense of ventilation apart from that weave at the start.
Run 5: Getting dark now. Swam ashore to do a BBC radio interview whils the boys towed VSR2 up to the top of the course. The sun was setting and I wanted to do one more run with the new trimmed foil before trimming another 15cm off it.
I ran up the beach to catch up with them and we pulled the wing up one more time in similar 26-32 knot conditions whilst the African sun set (first flamingoes present). One person. Good run with no weave or vibrations. Noted the hard surging of the boat which feels like it is pulling a lot of drag. Peak speed of 50.24 knots, (average 47.78). Damnit. 50 knots is boring now.
So, where are we? With limited footage and data downloaded I can still tell you that we are fully attached even with 15cm of main foil removed in strong, fully sheeted on conditions. No bad vibrations were felt although there was that big weave on the start-up and bear away of run four. We will look at that one more closely. It's pretty surprising that reducing the area of the foil didn't initiate the bad vibration but then maybe that was caused by other more subtle situations. I am keen to chop off another 15 cm. I want this thing to ventilate. We will discuss it further and sleep on it.
Overall it was a very good day. We pushed very hard in as strong a conditions as we should ever need to sail in. We did more runs than ever before and brought the boat back intact and ready for more tomorrow. Of course it's annoying that we didn't break through but days like this will create our end result. The whole team did a great job to keep the ball rolling and not fumble it.
Helena got a new PB of 48.87 knots but just missed out on becoming the second female ever to cross the 50 knot barrier on a sailing craft. I'm sure she will do it many times in the future.
In the end I had no issues with chopping the foil. Its only purpose is to go well over 60 knots and it simply isn't doing it. The rest of the boat is waiting for the right foil solution to set it free.
The boys have gone home after the other great team at The Raft sent pizzas, extra big burgers and some beers around to the container for the data transferring session. It's 20 to 11 now and we will be up and at it early tomorrow. We will double check and reconfigure the boat. The beam and rig will be moved forward in anticipation of the greater leeway angles generated by a ventilated foil... and most likely another 15 cm will be trimmed off. VSR2 will be re-measured for reference and calibration purposes. Then we will head out and do it all over again.
The good news is that Saturday is grunting up and may be useable.
It's not over yet party people. As always, we will push it right to the end. We aren't just hanging around here. From the perspective of our team’s performance today, we did very well. I doubt we could have squeezed much more out of the day. We just have to find what makes this dog hunt.
Two days to go. Optimise or breakthrough?
(Wed, 7 Dec 11 11:49)
It has been forecast to blow today for some time. The winds have been very light recently so this has been eagerly anticipated. I just walked outside when I heard the first rustlings of the wind. The first 'fingers' of breeze were finding their way across the glassy lagoon being led by a pod of dolphins. That has to be a good sign if you're into that stuff (which I'm not really)... but there it is, a pretty sight in anyones books.
We have been busy trying to understand what is going on with our foils and working out explanations for VSR2's behaviour on the last runs. I must thank those of you who have had input and put forward suggestions as they are all considered. There are some very learned people who know a lot more about some of these high speed phenomena than us so it really is great to apply their understandings to our situation. Whilst we still can't explain the tendency of the conventional foil to bear away hard at around 50 knots, there is a consensus growing regarding the performance of the ventilated 'wedge' foil. We believe that it is too big and therefore not travelling at the correct angles which would allow it to hold a stable ventilated cavity. When we get that horrible vibration it may be because it is travelling in a 'no-mans' land mode where it has lost grip but can't lose grip enough to hold a stable cavity.
It is obvious by the photos taken from the masthead (shown in the previous blog) that the cav/wedge foil is not 'sliding' as it is designed and therefore is not operating in the mode it should. The fact that it is travelling quite well with the water attached to both sides of the foil could explain why we have pretty good low and medium speed performance all the way up to 50 knots but are struggling to go faster. This odd foil is sort of behaving like a conventional foil. We did however go faster in one run with two people on board so really don't know what speeds it is capable of in this mode. We suspect that we will not be able to generate the angles of attack this foil requires to side ventilate i.e. shed the water off the suction side (probably somewhere above five degrees) unless we reduce the area of the foil. Cutting the foil is a one way path.
Now, based on the forecast, it looks like we may only have two good sailing days left before our current record attempt is over. Today and tomorrow. We may get some bonus days if the long range forecast changes but they are not obvious now and it would be risky to assume they are coming. This means that we have two paths which we can follow. We can try and purely optimise what we have in order to get the best result we can in this session, or we can make the call to go down the one way path of cutting the bottom of the cav/wedge foil and going for the breakthrough.
One 'optimisation' path, which has two options (one for each foil) is unlikely to yield an Outright record but may get us a few scalps further up the speed sailing ladder, the other 'breakthrough' path is perhaps our only chance of making the jump to realise the potential of the boat (It's great writing this down as it all starts to become obvious).
1/ Optimise Existing Option...we try and repeat the performance where we achieved 54.4 knots, improve on it and bag the 'fastest boat' and Australian record. To do this we use the cav foil and simply try and re-find that performance now that we have changed a few things i.e. stiffened it. To do this we will try a few different pitch and inclination settings.
2/ Breakthrough Option...If none of this works then we should proceed to chopping off the tip of the foil. The idea is to try and make the break from attached flow to ventilated flow. This foil is meant to work this way and it is not ideally suited for the way we are using it anyway. The consensus seems to be that it is simply too big to operate at the angles it requires to ventilate properly and this is causing this oscillatory flow where we are neither here nor there. This may well be the last time we ever use it so we should learn from it. Firstly remove 15cm to see what effect that has (we expect it will make it worse before it may make it better). Secondly by removing another 15cm (30cm total) to see what effect that has.
3/ Old School Option...Try again with the sub-cav section. Two additional fences have been added. One at half-way around the transition and the other 25% down the second foil.
In a perfect world we would have a great couple of days that allows us to do eight runs in similar ideal conditions so that we could scientifically progress through the above options in order. This way we could have our cake and eat it too.
If these are our last two big days then we do want to leave here having made every effort to glimpse the real potential of Vestas Sailrocket 2. This boat is designed to drag a super-ventilated/cavitating foil through the water over 60 knots. If we only manage to make a few runs then I may have to make the bold call to chop large chunks off the very expensive and difficult to replace ventilated foil and just go for it. I know you're all probably reading this screaming 'Chop it. Chop the bastard now with a blunt axe!!! We want 60 and we want it now (in HD preferably)'. Well, it's on the cards (the hacksaw is packed and the lines are marked on the foil) but the thing is that it may well not guarantee a result. The foil may just be wrong. It may prevent us from even getting started. It will however give us a point on the graph to reference future design decisions against. If it fails then we go down the 'old school' path.
So, we will see what we get weather-wise and take it one run at a time. We do need to be lucky on this front and it is out of our hands. The conditions may well not lend themselves to our proposed scientific method. We still have so much to learn.
A bonus sailing day although no big numbers!
(Fri, 2 Dec 11 20:24)
Today developed stronger than we expected although we were ready to get out there. As the wind started to whistle we switched from data processing to 'gig's on' mode.
Obviously the results from the previous session has been on our minds as it showed that we have some big issues to resolve... but we also have a heap of data to point us in the right direction.
Take these two pics for example...
There is just an immense amount of info in these two shots. They are taken in very similar conditions at very similar speeds... with two totally different main foils plugged in. The top one is the one with the cavitating, wedge shaped foil and you can see how close the foil is tracking to the bubbly, ventilated wake of the rudder. It's almost in it. The lower photo is with a conventional foil and it is travelling well clear of the wake. The rear pod is flying in both and the fixed angle (but self-retracting) rear skeg in the back float is just kissing the crests. You can see the wave impacts of the front float as it jumps across the crests. The fact is that the Cav foil is built with three degrees of angle in it as it was always assumed it would be travelling in a fully ventilated/cavitating mode. these shots show that it clearly is not. The flow is most likely fully attached back to the base of the foil and... it's performing quite nicely. The trouble is that it's now subject to the standard foil issues and that won't give us that glorious sonic 'boom' that we crave. All good evidence.
The rudder loads were similar for the two runs with low loads around 5-30 kg. This would suggest that loss of grip at the front/rudder was unlikely. What is interesting is how submerged the main foil is in both instances. Vestas Sailrocket 2 should be riding on her transition. This is the curved section of the foil. Instead she is sitting much lower with a large part of the 'first foil' (the upper more horizontal foil) submerged. This suggests that the foil is pulling down too hard... or we have stood the rig up too much to stop the leeward pod from flying and thus reduced the net up lift... blah blah blah. I could go on... really I could. I hate to cut it short for you techno heads out there who are no doubt getting right into this... but that's how it goes when the wind starts to blow and you have to drop everything, make a quick call on what changes will be best to try out and then get out there.
That's what happened today. I was calling Chris and Malcolm whilst climbing into a Musto drysuit and discussing options. I had already reduced the incidence of the main foil and pitched it up slightly. This should reduce the downforce and create more lift on the upper horizontal foil section. I discussed with Malcolm the possibility of quickly 'whipping off' the bottom of the foil... but we had no time.
We got over to speed-spot. Conditions were gusty and shifty. We had wind peaks to 27 knots but lows to 17 and the angle was changing. I knew it wasn't record breaking conditions so didn't spend ages with the details of the boat. It was going to be a day for collecting more data and trying things out. Helena's seat was fitted in the back. many of you have mentioned the fact that we went faster with two people on board. It doesn't make sense... but we can't discount it yet.
I did the first run one-up. I didn't feel that previous horrible vibration although the run wasn't that fast. There were some big holes in the wind. I noted that the foil seemed to be travelling higher. I did the full run. It wasn't strong conditions.
Foil is definitely riding higher. We are now right at the start of the transition radius here... even lighter conditions.
We tried a second run with Helena onboard.
It really was such a pleasure to be finally sharing the experience with her. Christ she has put in some work... and faith in this project. We didn't get going as the wind began to fade but in a way it really didn't matter. I really enjoyed that and we will share the speed later.
So a lot more was learned. Data was gathered and we are coming to understand certain aspects of what we have on our hands a lot better.
I love reading all your input. I can understand how hard it must be from the reader’s perspective not to have all the data we have to form an opinion on. The thing is that the picture is constantly changing and one opinion can fade with a new bunch of data or by slightly adjusting the timeline which changes the order of things.
I still believe that we can do this. The boat itself is awesome and it constantly takes us up to the record door for us to knock on it. One day we'll get the combination, burst on in and trash the joint.
I love this laboratory.
The weekend looks pretty windless. It might be time to get away for a day or two before we go mad. The wind will come next week. Vestas Sailrocket 2 is in great shape. The brains trust are at it back in the UK. Today was a bonus and I think we made an improvement. all is good.
Sailrocket 2 website
by Paul Larsen
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10:37 PM Wed 7 Dec 2011 GMT
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