Another big push for the elusive transition. It's getting interesting now.
Fri, 9 Dec 11 07:04
It felt like it was going to blow all day... and it did!
We got in to the container on the lawns of the Walvis Bay Yacht Club early and quickly pulled VESTAS Sailrocket 2 out of her soft hangar. The wing was up in no time and Alex set to raking the whole beam and wing forward 6 degrees in anticipation for the loads that would need to be balanced if today we found the long sought after ventilated flow.
When the water breaks away from the suction surface of the foil and air is dragged down from the surface to create a cavity, It can be described as being ventilated. It can happen on any boat when the foils are used too hard and there is easy access to the surface i.e. transom hung rudders stalling whilst rounding marks. Now when one side loses grip, the other side, in this case the pressure side, usually has to do all the work. To do this it has to increase its angle so as to have a greater effect on the water around it. This is why the leeway angle of VSR2 increases when we step to ventilated flow.
Nick chopped another 15 cm off the tip of the 'wedge' foil so as to increase the area loading on the foil and hopefully make it lose grip and become ventilated. It is designed to be ventilated but has been operating in an attached flow manner to date. This has shown itself to be relatively fast... but it won't get records.
The day built strongly as expected and we headed across the Lagoon to speed-spot around 1 p.m . I rolled straight into a run figuring that it might blow out on us so best to get some runs in as soon as possible.
Run 1...
1 person, 30 cm removed from ventilating/wedge foil, 21-24 knots of wind, beam raked forward 6 degrees to 77 degrees.
Surprisingly easy start up and good acceleration for such a short foil. No doubt assisted by raking the beam/rig forward. Good control but nothing special speed-wise in the lightish winds. Peak speed 45.06, 500m avg. 42.44 kn. Actually quite surprised by ability to start up and go in such light winds with such a small foil.
LOOK MA, NO HANDS. VSR2 CRUISES ALONG IN THE MID-LOW 40'S.
Run 2...
1 person, same configuration as above but much stronger winds gusting to 29 knots. Another easy start up with good acceleration. Good control, no wierd noises or swerving. Foil felt draggy. Peak speed of 47.8 knots, 500m Avg. 44.71 kn.
This obviously wasn't working. That was windy and the boat was sailed as it should be. I was tempted to chop the foil again right then and there but decided that it would be best to try a big change to the foil configuration first. I used the full range of the pitch adjustment in order to angle the foil nose up as much as possible. The idea being to force the upper, more horizontal part of the foil to both lift and ventilate more. If this in turn makes VSR2 ride higher then the foil still in the water will have to work harder. Because the upper section of the foil now has a high angle due to the increase in pitch, it should ventilate and feed the air around the bend to the lower section of the foil more deeply submerged. That was the theory and this foils best chance before it would get the next big chop.
Run 3...
1 person, wedge foil with 30 cm removed in full pitch up mode. Very windy with gusts to 34 knots, solid spells over 30 and lulls to 28.
Had trouble launching the boat as it was just too windy. VSR2 launched hard from the nose tether to the transom tether and the boys in the support RIB couldn't hold it. I was dragging the RIB. The wing was stalled and VSR2 rolled to leeward. The whole leeward float submerged and the horizontal wing extension dug in the water. I eased the sheet quickly to unstall the wing and pop the float. The boys had set the tether free but I was no towing 30 meters of rope out the back. Fortunately no damage had been done to the wing extension. I pushed on with the run. From my perspective there was still no noticable difference although from the pics you could see the back of the boat riding higher. I could still feel the foil dragging hard with no tell-tale swerves to tell me she was letting go into a fully ventilated mode. It was damned windy and rough. We struggled to pull the wing down. 46.72 max, 42.31 avg.
As we headed back up the course I felt enough was enough. We pulled into the timing hut. Helena confirmed gusts now peaking at 35 knots. This was now officially bullshit. First we have long spells of no wind and then two days with over the top conditions. Something in the middle would be nice for a change. The trouble is that VESTSAS Sailrocket 2 is so well behaved and managable that you can easily be tempted out in conditions you simply shouldn't be in simply to try and use brute force instead of sophistication. It's not a bad card to have up your sleeve mind you. If that's what your given then you casn play it. I set the limit at 35 and was happy to stick with it. We had two issues on that last run where we nearly had damage and it was only due to general handling in very strong winds.
I had seen enough. This foil wasn't letting go so it was time to chop another 15 cm off. This was now 45cm in total and over half of the main foil. It's not the ideal way of getting a smaller foil. It's pretty brutal in fact but this foil isn't working as is and drastic measures needed to be taken in order to find this ventilated flow. The foil now only had 30 cm until the radius of the bend. there wasn't going to be much left in the water. Maybe it was a step too far.
I pondered all this whilst we sat and waited to see if conditions would abate. It blew it's arse off for about 70-90 minutes before I saw longer steadier spells back down in the high 20's. The call was made to go for it again. We are on a mission here.
It was pretty rough just heading up the course and there were still some strong gusts around. The foil looked really silly now. Of course I had doubts... look at the thing and consider what I was about to try and do with it.
On the other hand this was perhaps the last windy run for this record attempt before we head back to the UK. we need to understand what works. We have learnt so much and already accept we need to try new foils. This would perhaps be the most educational thing we could do with this foil here and now.
As the RIB lowered me out onto the course I mentioned to Jeff over the helmet comms 'well, this is why you put harnesses in these things'.
Run 4...
1 person, 45 cm removed from wedge foil, full pitch up. Winds 25-31 knots. To my great surprise, VSR2 still managed to start up and accelerate pretty well even with so much foil now removed. The back of the boat was riding much higher but it all felt nice and stable in the cockpit.
THE REAR FLOAT IS RIDING HIGH AS I ACCELERATE ONTO THE COURSE. WE WOULDN'T WANT IT ANY HIGHER AS IT DECREASES THE PITCH ANGLE OF THE FRONT FLOAT. HIGH 'PUCKER' FACTOR HERE.
Due to the rough water I tried to get in nice and close to the shore. I could still sense the drag. I was a bit nervous about this run as there really wasn't much in the water and what was in there was a rough stab. Just past the timing hut I could see a gust on the water.
THIS LOOKS TO ME LIKE IT'S DIGGING A DITCH BUT WE DON'T HAVE THE LEEWAY OR CORRESPONDING RUDDER ANGLES TO BACK THIS THEORY UP.
VESTAS Sailrocket 2 accelerated hard. It felt like I was being released from the drag. It felt like something was changing. I quickly considered what the hell I was doing and eased the sheet.
The run had been too slow to start for a record run and we were running out of course as low tide was upon us. I could potentially be closer to the edge than I knew. It was a good peak speed that could have been much higher with a second similar run. Peak speed 51.41 knots, 500m avg 46.57kn.
The wind had continued to drop into the low medium 20's and the sun was heading for the horizon. It was too late for another run. So that was it. We had pushed hard again. Maybe with that last 51+knot surge we had glimpsed a transition but I can't be sure. Now that I have looked at the masthead camera... it still looks like the foil is travelling close to the forward rudder wake. That tiny little, high riding, unfenced, stumpy, thick-as-hell-tipped wedge that I still call a foil had just ripped out a 51 + knot peak and not ventilated. If it was ventilated, then why is it pulling the boat harder to windward than the large conventional foil? Christ, we have 4 fences on our long conventional foil to try and prevent any ventilation and this little thing just goes and does that. Right now I'm a bit lost on that one although I already have theories how to improve what we now have. It's late, I'm tired and I need to talk to some people. All I know is that our next foils are going to be tiny in comparison to what we have now. I know now that we can get started with a lot less than we expected. You always learn something extra on the side.
So we have 1 week left now. One week with no big winds forecast. Things change and a one week forecast can't be treated as fact. We will, as ever, go forward with optimism. that last surge was encouraging. It was the best peak in the last two days which started with a full foil. We still haven't finished with the conventional sub cav foil yet either.
Yes... it is frustrating to not be hitting the big numbers.
Another big day in the speed sailing lab. Every result is a result.
Cheers, Paul
Punt the foil?
Submitted by P.Flados on Tue, 12/13/2011 - 04:30.Your current attempt continues to impress me with your resolve and diligence in the face of a barrier that does not seem to want to budge.
The big French boat is at a totally different scale and I am not sure if there is much you can take away from their abilities to exceed your current max.
The opposite end is the kite crowd. If you real wanted to, you could try to borrow (steal?) from their successes.
A main foil that duplicates the surface slicing action of a kiteboard would not be a challenge to build. Maybe something with a more triangular profile. You have a perfectly good structural stub that is getting kind of close to be just right to mount something new on the end.
However with the surface slicing approach, you would probably loose any down-force available. And like it or not, lift (up-force) may come with the choice.
Then again, if your main foil stub was producing much down-force on the last run, you are at a real risk of having it pull out of the water at any time.
With the recent runs, rear hull altitude control may need a re-think. A horizontal airfoil (tail) at the end of the hull with feedback from a wand could give you some active altitude control. Alternately, put say 2 meters of extended profile flap on the back of the crossbeam near the hull. Design in rear hull weight (ballast) and a surface slicing foil designed for a specific up force at the right submergence.
The combination above could give you firm control of rear hull ride height with minimum changes while allowing you much more freedom to try going around (instead of through) the current barrier.
Getting your cav on
Submitted by Roo on Sun, 12/11/2011 - 19:22.Been following your progress since the early days and willing you on from the Gorge to crack the record. We've played with some cavitating foils (Curtis and I have been working on fins since the first windsurfing speed records back in 1988) and one thing we found is they don't glide very well, as soon as the power comes off drag builds quickly. You have to man handle them to start working and drive them hard. It seems from your 2 fastest runs this is what you had unwittingly been doing.
Sat, 12 Nov 11
For some reason VSR2 stubbornly refused to bare away. I oversheeted to the max but she wouldn't turn. She was sliding sideways pretty rapidly and the leeward pod was dipping hard.....Finally a wave combo helped the nose turn away from the beach and we dropped into mode. The start up was quick and the acceleration came fast. There was one surge during the bare away onto the course which was remarkable.
Max speed (doppler)- 52.13 knots
500 meter average- 49.22 knots
Thu, 20 Oct 11
With all the drag on the front float of VSR2, it resisted sliding sideways to help me bear away onto the course. I struggled to get the nose to bear away and every time I sheeted out to get the flow attached to the wing, VSR2 just turned more into the wind. I was now sailing back into the shore and running out of room. I way over sheeted the wing to windward to stall it and perhaps force the nose of the boat to bear away. With all the drag it stubbornly refused. I got Adam to release a small control line in the back cockpit which allowed me to over sheet some more....Sure enough we managed to bear away and slowly slide sideways away from the beach....
Max speed (doppler)- 53.92 knots
500 meter average- 50.05 knots
The common denominators in those runs were sliding sideways unable to turn the boat and oversheeting to steer it onto course. Even though you weren't up into the speed range to get cavitating you had somehow pre ventilated the foil. I know from windsurfing it's easy to vent the fin by oversheeting or too much back foot pressure at low board speeds and I believe that is what you did.
The key to cracking the cav beast may be to pre vent the foil either by introducing air down the foil or by overpowering it at low speed.
All the best in your speed adventure, good to see a fellow Aussie taking it past the limits.
Roo
PS. I developed the GT11/31 GPS back in 2006, it's not a bad little unit for what it does but no match for the mighty Trimble you have onboard.
Serendipity?
Submitted by oldie on Sun, 12/11/2011 - 12:39.Brave you are, Young Larson, to run that machine with only half a foil, as it would appear to be the only thing that prevents a grand capsize fall..
To add to the wild theories, could it be that the ventilating rudder is preparing the water for an interesting vortex dominated environment which suppresses cavitation?
The kiters may already be unknowingly onto this, with the front skeg on their long boards being tracked by the rear..
Good quote; Kiteboarder's foil solution?
Submitted by Tim on Sat, 12/10/2011 - 21:26.Paul's new quote that I'm going to commit to memory: be careful not to confuse intuition with traditional indoctrination.
I continue to be impressed with your cav foil thoughts and developments as you chase the speed record. Aside from intuition (which I try hard not confuse with entrenched habits), I'm about out of ideas save the following.
Viewing your pics of the steadily diminishing cav-foil, I can't help but think that VSR2 is presently steering you towards a thought I expressed several weeks ago regarding the manner in which kite-boarders deal with the kite-forces while maintaining direction/helm at high speed in their narrow trench.
Arguably, the kiteboarders at 50+ knots are not using any portion of their bottom-mounted skegs/fins to oppose kite forces and maintain direction. Instead, they appear to be using the entire windward rail of the kiteboard as a highly adjustable, but fully ventilated, centerboard/foil. The kiteboarders don't need to concern themselves with cavitating foils deep in the water simply because they can oppose kite forces and maintain direction by using the windward rail of their boards to push a lot of water/spray downwind.
In the most recent VSR2 stubby cav-foil pics, I wonder whether VSR2 is suggesting a direction to move with the R&D of your next foil: a wide and shallow edge (i.e. a long length along the water line) who's angle to direction of travel can be adjusted and controlled, versus the present, high aspect (narrow and deep) cav foil?
More thoughts from the peanut gallery.
Tim, Vermont
stiffness
Submitted by Florian Prevel on Sat, 12/10/2011 - 20:09.Hi Paul,
Some problems appears after the reparation of the high speed foil. And your best ride was just before this reparation.
When you have repaired this foil you have increase the resistance, but also the stiffness (reduction of deflection).
Imagine that the foil is not working like in theory and that the theorical angle are wrong.
On your best ride, your foil was broken (more flexible), your were 2 onboard so load is bigger. So the deflection of this foil was not control and his angles were not planned but it works quite well.
You repair the foil, everything come back to the theory but it doesn't work anymore. You feel a vibration, maybe a resonance but resonance is link with the stiffness !
Maybe you can try to change the angles, and to put the boat in a configuration similar of what had happen with the "broken foil".
best regards
Stiffness
Submitted by Tim on Sat, 12/10/2011 - 21:31.Florian, I too had wondered whether the foil stiffness following the repair had caused some small but critical change in the cav-foil performance. Yes, the fastest ride was also the last ride before the repair, but remember also that the cav foil grounded in the soft bottom at some speed at the end of the fast run. I wonder whether the cracks in the foil that Paul repaired could have been caused by that grounding in the shallows, which, if true, could mean that the cav foil performed as it should have during the high-speed but un-optimized run. It seems as if VSR2 has hit a 50 knot barrier ever since then.
Tim
Second Person
Submitted by james on Fri, 12/09/2011 - 21:46.Paul,
I remember you had one run, maybe a month ago where you had a passenger. I believe you hit a 50 knt peak and were not fully dialed in at that point. I'm wondering if having additional weight in the boat will give you a bit more momentum to keep the boat moving between gusts.
I'm waiting any day now for the "We Did It" email. Good Luck, James
REPLY... second person...
Submitted by Paul on Sat, 12/10/2011 - 10:34.Hi James,
We did the second person trial the other day and there was no significant difference. VSR2 is a bit slower to take off but once she is away I can barely notice it. We are now getting Helena used to the cockpit so she can drive and I can sit in the back. This is all leading to me getting out of the boat and watching it for once. It will be about 30 kg lighter up there with her driving. I still can't quite explain that very fast run we did two up. I can't wait to send that 'We did it' e-mail. One day James, one fine day!
Cheers, Paul
armchair comments
Submitted by geoffj on Fri, 12/09/2011 - 18:00.Dumb questions from the cheapseats: If you are expecting the foil to initiate ventilation from the surface with air travelling down the trailing (blunt) edge, is the foil blunt above the radius ? What force is the water applying to the foil above the radius? Are you expecting the foil to maintain a ventilation cavity from tip to surface? If so, how are you maintaining even foil pressure around the radius?
It seems to me that a radius in the foil perhaps preventing a consistent ventilation.
REPLY... armchair comments.
Submitted by Paul on Sat, 12/10/2011 - 08:56.Yes, the foil is blunt above the transition (radius). The foil above the radius is affected by both the leeway angles of the boat and the pitch settings of the foil. Seeing as the upper foil is at 30 degrees to the HORIZONTAL, the horizontal pitch settings affect this section of the foil more than the more vertical lower section. The upper section of the foil is more responsible for generating vertical lift. If it generates too much then the back of the boat rises until we reach the transition (radius) of the foil where the vertical component lessens. If we go too far then only the bottom section is left in and that is angled so it is pulling down more than the rig is lifting i.e. we will have net negative lift and be pulled back down to the transition. The boat should seek balance around this transition. If we are riding too low we can increase the pitch of the foil to generate more lift on the top section or decrease the whole inclination/roll of the foil. Getting the right settings is key to making the foil perform. We are still playing with it.
Cheers, Paul.
Foils and rig balance
Submitted by Mike Ewart on Fri, 12/09/2011 - 17:20.Hi Paul and team, I also am a bit confused about swinging the wing forward and would have been thinking about reducing the width of the foil not the length, if as it looks likely now you have to go for another attempt can you introduce air passages into the foils and look at different configurations in width/length, good luck for the rest of the week as you said the week long weather forecast is only a guess at the best so there is still a chance of a few more runs.
REPLY... Foils and Rig balance
Submitted by Paul on Sat, 12/10/2011 - 09:25.Hi Mike,
VSR2 is expected to travel at higher angles of leeway with the ventilated foil as the foil needs to make more leeway to deflect the same amount of water of only one surface. In order to get all the forces to allign to this new boat orientation, we need to rake the beam forward a few degrees. It also assists in helping VSR2 bear away during startup. If VSR2 doesn't make leeway and the beam is too far forward then we get higher forward rudder loadings as the boat acclerates and the apparent wind moves forward. We use the rudderl loadings to see if we have the balance right.
We would love to reduce the width and thickness of the foil but unfortunately the structure would be compromised as the outer shell has all the 'off-axis' fibres responsible for torsional stiffness. However, now that we have lost a lot of the span and have a very thick foil, maybe we can do this. I'm not sure if we will get the chance now.
Cheers, Paul
Easy startup, foilsize and planing?
Submitted by Arvid on Fri, 12/09/2011 - 15:21.Is it only me who aren't surprised by easy startups with a smaller foil? I may not understand fully what is happening, but shouldn't a smaller foil logically produces less drag then a big one? Since your boat got a low weight compared to power, it should be planning at low speeds anyway, and as far as I know, the fastest motorboats are planning. Given this, lifting your hull from the water shouldn't significantly reduce drag, so I would think that you get less drag as you shorten the foil of your craft, even though the hull may lift from the surface later. Isn't the main reason for you to still have a foil to just counteract the drift of the wind?
Another thing I wondered about was why you think that a smaller foil should produce a higher pressure and from that cavitate more easily? Given the same speed, you get the same hydrodynamic force per unit area, resulting in the same pressure on the foil as before. It could lead air down more easily from the surface though.
REPLY... easy startups, Foilsize and planing
Submitted by Paul on Sat, 12/10/2011 - 09:43.Hi Arvid,
In some ways a smaller foil should produce less drag but it does depend heavily on what you are wanting it to do. You also want to get lift out of the foil as well. A little foil may produce little drag at low speed but it will also produce very little lift... especially at low speeds. In order to produce enough lift to counteract the side force of the wing it has to travel at higher angles of attack and this is when small foils give up and stall. At lower speeds you typically need bigger foils than you do at high speeds. If I could simply run away downwind with the wing fully eased then I might be able to get away with really small foils during the start-up but we are somewhat limited to our downwind angles by the angle of the back shroud to the wing. If I go too far downwind I can overload the wing strut in compression. It was easier on the first boat which had a great shroud base for the backstay.
On the other points, the less we have in contact with the water the better. The main foil is designed so that it carries the weight of the boat and reacts the side and vertical lift generated by the wing. It's much nicer to use one foil instead of two. Biplanes aren't quick.
With a smaller foil you will get a higher area loading. The same foil will try and do the same work as a bigger foil. As mentioned above, to do this it will travel at higher angles which will manifest itself as greater leeway. This will increase the pressure PER SQUARE INCH relative to a bigger foil. Not only will the pressure increase on the pressure side, but it will decrease more on the suction (upper) side and this in turn should be more likely to ventilate or cavitate. The smaller the foil for a given speed and load, the greater the area loading. A shorter foil is closer to the surface and therefore is more likely to fully ventilate than a deeper submerged foil.
Cheers, Paul
Keep Going Boy's and Girl
Submitted by nicolas on Fri, 12/09/2011 - 13:16.Thx for the feed back.
Very interesting stuff, all the way...Nice to see that boat is behaving well and helps u to test things...
Nicolas, Brussels ;)
Fine tuning
Submitted by Snailor on Fri, 12/09/2011 - 13:12.Hi, as usual when observing a really cool project from afar, its looks 1000 times easier to fix things than it really is by far.
But I dont understand why raking the rig forward in strong winds would help, when speed increases so does the drag in water, the craft would then like to pitchpole forward wouldn't it? Intuitively I would rake it backward or move the whole thing further back.
About the rudder wake, perhaps the angle of attack is too aggressive on the main foil, perhaps it would be less diturbed if it was pointing less upwind i.e. 4 degrees? Or just mount the rudder further to starboard...
A new smaller cavitating mainfoil I believe will definately get you beyond speedlimits, since the drag is proportional to the sqare of the speed and area approximately.
Please correct me if I'm wrong, Go Vestas team!!!!
REPLY...Fine tuning...
Submitted by Paul on Sat, 12/10/2011 - 10:20.Hi Snailor,
We aren't really raking the rig forward so much as swinging it forward. the pitch angle of the rig stays the same. It's more like moving your mast forward on a normal boat.
Be careful of intuition as it can be confused with traditional indoctrination. That's partly why we sat in the back on VSR1 and it was actually one of the biggest flaws in the boat. 'Intuitively' it was the right place to put the weight. It wasn't.
Because the rig is so far offset from the foil, you have to be very careful where you position it or else it will start creating large turning moments in the boat. These moments can only be corrected by the rudder. The rudder loads are all measured and we use these load measurements to set the boat up.
The angle the cavitating/wedge foil is set at to the main fuselage is 3 degrees less than that of the conventional foil. This was done as we were expecting much greater leeway to make the difference. The fact that we are not seeing that and this foil is travelling much closer to the rudder wake confirms that this foil is not ventilating. Basically it's not working and changing the angle RELATIVE TO THE BOAT will not necessarily fix it other than move it away from the rudder wake. The angle of attack relative to the water is a different thing and that is generated by the side load from the wing and the overall efficiency of the foil itself. We do need to try new foils and yes we do believe that we will reach the designed speeds once we get it right.
Cheers, Paul
foil tip?
Submitted by simsimian on Fri, 12/09/2011 - 11:00.Hi Paul, Helena and team
Fantastic job you're doing. It's great to follow too. I am a completely ignorant armchair fan, but could not help wondering about the impact of that blunt foil tip. Any thought about putting an anti-vortex wingtip (a la commercial jet) on there? Forgive me if that is contrary to the concept, because I have to confess I don't fully understand where the ventilation is initiated and how it is kept stable.
All the best from sunny Bristol
Simon
REPLY... Foil Tip...
Submitted by Paul on Sat, 12/10/2011 - 10:26.Hi Simon,
Now that we have such a low aspect ratio foil, wingtip fences are probably more relevant than ever. Yes we are considering it although we may run out of time on this session to try it. We are definitely losing a lot of energy there. The funny thing is that if they work... we may need to make the foil smaller again as we have increased the efficiency of the thing and this in tune generates less leeway and perhaps less likelihood to ventilate. It's all trial and error out here now and we are running out of trials if we haven't already. We have learnt enough about other aspects of the foils performance to completely re-design the foil with the potential for very big gains in efficiency. I will be happy to scrap this one but will try and get the most out of it if given the chance.
Cheers, Paul
paint
Submitted by rvdokkum on Fri, 12/09/2011 - 10:29.Again, I'm not an expert on these matters.
The only thing on my mind is.... it must be possible....., it must be possible....
if you need to know how the pressure of the water on the foil is behaving....
why not paint the foil with paint that easely wears off due to the watter and cavitation.
So after the run you can see what parts were hit hard and what part not.
You can even use more layers of different color to see more detailed patterns.
All the best to the design team.
Looking forward to the comming days.
You can have our wind :) we don't need it at the moment.
Greets from Amsterdam / The Netherlands.
Remko
REPLY... Paint
Submitted by Paul on Sat, 12/10/2011 - 10:29.Hi Remko,
If you have some piant that does the job... we'll take it. I am happy to try anything that might clearly illuminate what is going on.
Cheers, Paul
Welcome to the 50 knots Barrier
Submitted by Uwe Sieg on Fri, 12/09/2011 - 10:11.Hi Paul
In my books, Thursday was your best day yet. Look at what you got out of it:
1) Realisation that the Cavitating foil does not behave as predicted:
(Please ask Mathias Roettcher to show you the speed fins we are using on Winsurfers. They have a very high aspect ratio and work well at high speeds.)
2) Analysing potential catastrophic handling problems: Handling of all equipment in Winds at 30 knots is tricky, to say the least. The air in itself is extremely turbulent and shifts and changes constantly. The kinetic energy will destroy a carbon mast in seconds if given the chance. (Wan't me to show you one?)
3) Realisation that drag is mainly confined to the foil ie everything else seems aerodynamically optimised.
Now is the time you have to dig deep even if it feels you are going nowhere. I think if your design team can dream up a better foil, you will see the difference.
Well done. JUST KEEP COLLECTING AND ANALYSING DATA.
See you on Saturday
Uwe