Well it's been a full old year in the world of the VESTAS Sailrocket program. This time last year I was using the quiet Xmas period in the build shed to get all the spray-painting of the wing out the way!

We launched on the 4th of March and shipped the whole jam packed container to Namibia a few days later. After some low speed teething issues we drank the 20,30 and 40 knot bottles of champagne on consecutive days. Within 23 days from launch, this radical and highly compromised, one-off prototype boat was hitting over 50 knots. What's more, it was doing it using an unconventional ventilated foil section.

The VSR2 program is focused on making the breakthroughs necessary to overcome the conventional limits of high speed sailing. These are all centered around the performance limits of conventional foils. The kite-surfers don't rely so heavily on these and therefore, as they have so clearly demonstrated, they don't have the same limits. In order to test and develop foils at very high speeds, you need to fund, design, build, develop, maintain etc a craft that will allow you to repeatedly enter the 'laboratory' in a safe and reliable manner. This year I think we demonstrated that we have the right craft. At the end of the last session a couple of weeks ago in Namibia, we had shown that VSR2 could drag almost any foil we bolted onto it down the course at speeds over 50 knots. We were constantly banging our head agains the old limits. It does seem that many different craft and projects get stuck in the low 50's. We didn't make the breakthrough we were looking for this year but we are very definitely in the right laboratory with the right tools.

20/20

Now that I can look back, I can see where some of our assumptions were just plain wrong... but that's ok as our understanding of the bigger picture is right on track. The boat is great and it is only the highly modular foil that is wrong. It was our first shot at a ventilated/cavitating foil and assumptions had to be made. If we were just doing 60 knots then it would have been a lot easier. If getting through low speed transitions just involved pouring more fuel down the carburetor then it also would have been easier... but this is a sailing boat that has to accelerate from standstill using only windpower so the problem is a whole lot more intersting. Now that we have a whole heap of real world experience we feel that we are much better placed to re-visit the problem. Of course we are. VESTAS Sailrocket 2 is currently sitting all nicely packed away down in Namibia and can be made ready to do 50 knots plus again within a couple of days. All our efforts now are focused on getting the foil right.

SOLUTION

After our design meeting hours after landing back in the UK,

CHRIS, GEORGE, WANG, MALCOLM AND PAUL...

the current thinking is that we will scrap the L-foil configuration and go to a T-foil arrangement.

FIRST SHOT AT CAV FOIL ON LEFT AND PROPOSED T-FOIL ON RIGHT.

This foil does seem to have many advantages. We had discounted it previously as we though that the end plate would need to be much bigger to enable us to generate the low speed side force to get started. This would have meant that we would have had structural issues around the junction... especially if the top tip of the foil popped out of the water as this would put large torsional loads on the junction. Now that we believe we can go a lot smaller (as demonstrated by our 'chopped down' runs towards the end of the last session), we believe that the 'T' configuration has many benefits...

-we can use the existing composite 'head' of the foils.

-we can machine the new components out of metal which is far cheaper, quicker and will allow us to try many variations.

-we can make the foils much thinner as the bending loads are greatly reduced

However, there are issues that we need to resolve. Some of the aspects that need to be considered are as follows...

-what dimensions will we need to satisfy all criteria?

-what are the expected loads for all scenarios?

-What are the realistic performance expectations?

-How do we best gain the understanding of how the foil will perform and make the necessary flow transitions?

-if we do still want to use ventilation as a means of creating the upper surface cavity on the foil, how do we ensure it can get down to the foil?

-how do we maintain good ride height?

-How do we reduce the drag at the junction of the T as these junctions are always messy, especially when highly loaded.

There is just so much to learn. We have started by working on a 'T-foil' based spread sheet that will show us the effects on the various balance/load/ performance factors from changing various inputs. This shows us the basics. From here we need to understand how the one foil solution will make the transitions from standstill to over 60 knots in a sailing environment. The final foil solution needs to tick a lot of boxes. Whilst I have no doubt that our team could work through the problem if given the time and resource, I feel that it is time to start really bringing other brains in to help us solve these very particular problems. I know that our endeavours have been followed by some very clever people who are quite passionate about this dark corner of yachting that we are delving into. In many cases we have been contacted and this is much appreciated. If I have seemed a little slow in getting back it is only because we are trying to structure the problem so it can be best presented to fresh minds. There are many good ideas out there but first of all, the specific requirements need to be outlined. The spread sheet will help us do this. If all the requirements are met to satisfy the basics, then we need to have a program which then allows us to verify this. That is still an open discussion as we don't know exactly what resource we can apply to the verification process i.e. CFD, model testing etc.

If the T-foil does make it through all this and the manufacture is as easy as CNC milling out flat foils, then this may well allow us to try many different shapes. We'll see. 

So here we are, heading into a new year and getting right down to the 'nitty gritty'. A world record would have been great but I can't allow that to overshadow what has been achieved this last year. Thankyou to everyone who has supported and encouraged us near and far. We will continue to share the journey even through this 'techy' stage as it seems that many of you find this as fascinating as we do. We don't intentionally hold anything back. Some times we just don't put things forward until we have some structured understanding ourselves. We don't feel we have too much to protect just yet as anyone who copies anything may well be simply copying our mistakes. VSR2 is still very much a work in progress albeit one that is more ready than ever for the challenges that await.

Have a Happy New Year and I'll see you all on the other side.

Cheers, Paul.

 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

 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 phenomenoms 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 5 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.

In a perfect world we would have a great couple of days that allows us to do 8 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.

Let's see what happens.

Cheers, Paul

 Walvis Bay rose to my challenge today and delivered a near perfect speed sailing day for us. This is why we come here.

VESTAS Sailrocket 2 is in the best shape of her life. The whole boat is starting to feel like a finished piece and I am really happy with her.

We did 3 runs today. The first one we did with the conventional foil in. We have added two fences to prevent air from getting sucked down from the surface. One fence is just below the bend (transition) and one is right at the top. It felt like I got ventilation on our last outing when VSR2 went into a big bear away so we added these fences to stop this.

The first run today went well and was very smooth. All the little details were making the whole experience so much enjoyable and as mentioned, it was near perfect conditions. The new launching system meant that I got up close to the beach much sooner than previously and this makes for a much longer run. The leeward pod was flying high but I was easily able to lower it using the flap control on my left.

The run was very enjoyable. Fast and effortless. Just after the timing hut she performed her old trick again and went hard into a bear away. I put in a couple of turns on the wheel to correct it and immediately stopped the run. Hmmmm. It would seem that fences didn't fix that then.

I still managed a top speed near 51 knots and a 500 meter average around 49.38 knots. This would be a new 'B' class world record for craft with our sail area... but I'm not that interested in that. I went faster with a passenger a month or so ago. We are after bigger game here.

Conditions were building so considering we hadn't discovered the magic to make that foil work I decided to do the ol' switcharoo over to the new ventilated 'wedge' foil. The guys had to go back to the container to collect it but in an hour or so we were back up to the top of the course and ready to roll. The start went great but even early on in the run I got this terrible noise and shuddering vibration coming from the main foil. I was only doing about 30 knots but there it was. It sort of felt like what I would assume cavitation would feel like. Not a cool or sophisticated noise... more like an engine throwing a rod! When I turned onto the course it smoothed out and the run went very well again. Once again I enjoyed it and it felt fast. VESTAS Sailrocket 2 is just effortless to sail now and I can savour the speed sensation without fear. She cruises at 50 like a car down a highway.

The, just past the timing hut again, she made that horrible noise which felt like running the tip aground on concrete. The drag pulled me from 50 back down to around 30 and once again I was forced to abandon the run. This was weird. Once again I hit a peak speed around 51 knots. This really is weird. I mean with effectively three different foils i.e. conventional-no fences, conventional-fences, ventilated, we have hit nearly the identical speed in very similar winds. Maybe it's a coincidence involving many factors but either way, there it is.

Conditions were still epic. It was just soooo flat along the shore. Gusting 28 knots and glassy in close. Pure speed sailing porn! We were so close to getting some bigger scalps than the B class record. I want to get the Australian record which is just over 50 knots and the unofficial 'Boat' record off Hydroptere which is around 51.4 knots or 2 knots quicker than my previous run. Either of those would be a nice way to finish the day. I stated the third run but once again I got that terrible draggy shudder. This time it was more persistent and I canned the run at the timing hut. I had only peaked at 30 something knots. What the hell was going on here. We went over the main foil and rudder but it all seemed fine. No obvious signs of cavitation. No damage. Basic boat settings. More Hmmmmmm.

we dropped the rig at sunset.

We have been sitting back here in the container downloading data and digesting as much varied info as we can get. We get a lot from each run. 6 High Def cameras, 1 Cosworth data logger, 3 GPS systems including the mighty TRIMBLE used for record ratification and a TACKTICK wind system with data logger. Multiply that by 3 runs and It's no surprise that we are still here at 10:30 p.m. having just downloaded it let alone digested it.

Funny thing is that I'm pretty happy with today. Breaking this record is like solving a big puzzle and today we got a whole bunch of clues. We did get some great data. The boat itself really impressed me. She is a real noble beast who now feels like she is trying to help us. The boys have done a great job sorting out the details on these windless days gone and I can really notice it. She's slick.

So we will digest all this new info. I already have a few things I want to querie. It appears from the masthead camera that the foil is running very close to the ditch created by the ventilating forward mounted rudder. It should be about a meter away. We have already double checked this whole aspect and remeasured it all to triple check. It seems very odd. Has VSR2 dropped into a mode of sailing that we haven't planned for and that she needs to be shaken out of. VSR1, our first boat, used to drop into a mode where she would drag sideways down the course at about 12-15 degrees. We couldn't believe it as it was still doing 38 knots. It was something you couldn't model or predict and yet there it was. Once we became aware of it and accepted it, we made the mods and began to unleash the potential.

I'm beginning to feel that there is something big we are missing here.

We are very definitely in the lab. We'll get to the bottom of this one. Two weeks to go from tomorrow. Come on Walvis, give us a few more like that.

Cheers, Paul