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.