Rasmus Køstner Talks T-Foils

Tell us about sailing with the new T-foils. What differences did you notice?

The first thing I felt was that they're very direct compared to the L-foils. There’s not a lot of movement or give from them. They're relatively stiff. So you feel like you are sailing with a little bit less ‘suspension’. That means it feels like your movements are translated directly into the boat. We could all feel it in the way the boat responds. We can see the platform is moving a lot more because the T-foils have a very nice grip and are very strong around the lifting area.

I feel like this is a foil that somehow requires a little bit less nuance. Sometimes on the L-foils when you wanted to push hard you quite quickly found yourself on the limit. Whereas with the T-foils I feel a little less at risk. You can be high, but you don't side skip in the same way as with the L-foils on the reach or upwind.

Does the boat feel ‘stiffer’ because the foils are titanium?

Yes, but it’s also the t-shape design. If you're trying to support something on the L-foils, it introduces a bit of flex – a bit of suspension, you might say. Then, with the T-foil, because it is not as big a span, it definitely has a very direct way of lifting.

What else is different?

The next thing was getting used to the new lift factor and the speed you need to do before you start foiling. Then you move into smaller details, like how much can you pierce (allow the outboard end of the foil to break the surface of the water).

I had some ideas about how I wanted to set up, based on what I thought would be fast. But then you really need to be eyes open as you calibrate that theory. You need to find out if the performance is actually what you suspected it to be, and whether your mental conception of it all matches with the real world.

Were you given a brief about the new T-foils? Some clues as to what to expect?

Not a specific briefing on what to expect as a flight controller, but we had quite a good documentation on how the testing went, what people’s impressions were on how the new foils performed – plus we could look into all the data on that testing as well. It was all very useful – super open and a good starting point. So I think everybody kicked off from quite a high level.

How much time did you have to get used to the T-foils before you first used them in a race?

During the training in New Zealand we had a couple of days outside of any racing where we were a little bit more free and in an open area where we could experiment a bit. I think what we experienced matched pretty well with what had come out of the testing.

Do the new foils change the way you sail the boat in other areas?

For sure. The way you might set the wing up could be different, the angles you might want to sail. On these boats if you change one component then suddenly you might need to revisit plenty of other things.

One thing that we have discussed a lot is leeway and the force you can introduce with the cant of the T-foil. Whereas before you were aiming for a high ride height so that you could induce a lot of windward heel in order to maximise your cant angle, now you can cant to an angle that is quite extreme compared to what was the case before.

We basically have an extra setting now, so that we are moving the foil in three directions. There’s up and down during the manoeuvres. The timing of that is really important and you also have to factor in that if you end up sailing on two boards you have a much bigger area and lifting force – but also a lot more drag. So one or two seconds earlier getting the old board up and out of the water gives you better performance and acceleration. I think that-foilt’s what a lot of the teams are looking at – during a tack or gybe how long do they have two boards in the water.

Then the third movement is the cant in and out of the board. Two dimensions was complicated enough – now with three there is even more opportunity for getting confused.

Are tacks and gybes very different with the T-foils?

The biggest difference is the dropping angle. Before we were dropping at the same cant angle and couldn't change it – whereas now we can. Now we can modify it for the conditions and even after that we can manipulate it as we're dropping. So when the board is up and stored, you can’t really do anything with it. But you are able to drop it at an angle different to the stow angle. Then you can still manipulate it from there, live.

There are a lot of things to look at and it's not obvious what exactly you want. The more you cant in, the more vertical lift you get, and the more you cant out, the more writing moment you get. So you kind of need to find the compromise there that gives you the best performance. It’s been fun to try to work it all out and experiment with it all.

What about starting? Have the T-foils changed how you sail the boat at the start?

We’ve discussed it quite a lot. There are opportunities for a little bit more glide, but we haven't really found the opportunity where we could use that. I'm sure there will be conditions where it will slot in nicely and you can take advantage of that. Overall so far I don’t think the starting technique has changed much yet.

Explain what you mean by ‘glide’?

In some wind speeds you can have a very nice lift stay on the foils for a long time at lower speeds with two foils in. I think that was quite a bit harder with the L-foils which were more draggy and lost speed a little faster.

It feels like from your answers that you are enjoying the new foils and the challenge of optimising your technique?

Yes I like them. We got off to a good start in Auckland where the conditions were wavey and pretty tough. We were able to push harder than I thought we would be capable of before. Being honest, when you are in a pressure situation it is way nicer having two or three years of experience on the foils, rather than just a few hours. The truth is that we get so little training time in SailGP that you need to somehow be confident enough with very little practice to go out and perform in the racing.

I think that is becoming a big factor on this circuit – where how you manage your limited training time becomes a discipline in itself.