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Jørgen Klaveness (2000)

Skimbat versus soft sails (kites and chutes)

Reflections after the Norwegian Skisailing Championship 2000

The article was written by Jorgen Klaveness, who has been an enthusiastic Skimbat wingsurfer since five years. Jorgen works as an lawyer in Moss, Norway. The other person mentioned in the article as a Skimbat wingsurfer is Gert-Jan Zeestraten, who made a contract with Skywings Ltd as Skimbat distributor in Norway early this year. Gert-Jan has opened a sailing school near Boda and he has a lifelong experience in all types of sailing. They both participated for the first time in the Norwegian Kite Championships, which have been arranged already for 8 years. Next year they are planning to invite Skimbat wingsurfers from Finland and Sweden to race against the kites.

I'd better admit it at once: I'm hopelessly in love with the Skimbat, and have been so for five years. This doesn't mean that I'm against other kinds of winter sails: Long experience has taught me that the Skimbat has some weak points, especially for uphill work in light winds, not to mention the relative ease, with which you can carry the soft sails along for improvised sailing "just in case it should start to blow".

I went to the Norwegian Skisailing championship 2000 hoping to impress everybody by the Skimbat's fantastic performance in high winds. I came back with a lot of lessons learned.

The Norwegian Skisailing championship is a regularly occuring event. It takes place late in the winter, on a corner of the "Hardangervidda", near Rjukan in Telemark.

Up to now, it has been totally dominated by chutes, kites and different kinds of small paraglider-inspired designs. This year, there were three classes:

1. "Up-Ski" large, large round chutes capable of downwind sailing only,

2. "Skiseil" with up to 11 sqm. sail area and maximum 8 metre lines

3. Kites (without design restrictions).

In addition, Gert-Jan Zeestraten and I made the first-ever appearances with Skimbats at the races, intending to compete with everybody else, outside the established class structure. We did very little sailing, due to poor wind and snow conditions, but we spent all the more time with the other guys, borrowed their equipment and listened to their stories. It was fascinating.

Wind, snow and race course conditions favoured the soft sails this year.

* On the first day, the wind averaged 3,0 to 3,5 m/sec, on the second day it was only marginally stronger (up to 4 m/sec average).

* The snow conditions were extremely bumpy, since the last heavy snowfall had coincided with warm weather and strong winds.

* Everybody seemed to take for granted that a downwind course would be not only easier, but plain necessary under such conditions. Gert-Jan and I looked at each other in amazement. If there's one thing we don't want in light weather, it's straight downwind sailing !

So, that was that for the Skimbats. On the uneven snow, there was nowhere for us to glide in the proper sense of the word, and the wind would hardly carry our wings. We got over the starting line once, while the "balloon chutes", "Skiseil" and Kites were all able to complete all their courses. Some of the kites managed to do so at surprisingly high speeds.

Next year, we're going to ask for separate racecourses across the wind and flat (or with a slight downhill gradient) in case of low winds.

Still, we came second on the max-speed contest. This contest was held on a light downhill run, where a skier without a sail would just glide slowly forward. The wind was not astern, but directly from the side. These conditions strongly favoured the Skimbat.

Top speeds (measured by a traffic policeman with a laser apparatus) were mostly in the 22-26 km/h range for the kites and "Skiseil" people. One skier with a relatively small kite stood out from the group, and made a fantastic performance at 53 km/h. All these skiers had to fight great sideways forces generated by their sails. None of them managed to

head directly for the polliceman and the laser apparatus; all were carried more or less off to leward. However, all of them were able to sail up the hill again.

The Skimbat performed in an entirely different fashion. It accelerated evenly all the way towards the target, and there was no sideways pull to speak of. We could have gone 30 to 45 degrees to windward without the slightest inconvenience! The speed was also far better than most of the "soft sails": We were repeatedly measured at 37 and 38 km/h. Compared with what the other participants went through, it was completely effortless. If we had used proper alpine skis, I guess that we could have gone a lot faster. But afterwards, we had to walk up the hill again.

I've always wanted a light-wind alternative for uphill sailing, so after the high-speed contest I spent a lot of time trying out soft sails. There were two alternative strategies that appealed to me: Medium-sized kites and large "Skiseil". First I tried a 22 sqm triangular "Skiseil" from www.skiseil.no. Later on, I tested two different kinds of kites from www.deltasport.com.

Both the kites and the "Skiseil" generated impressive amounts of pulling force. The 22 m2 "Skiseil" was 4,6 times bigger than my Skimbat, and weighed practically nothing. Spending no energy to lift itself, it had all the more left over for me.

The kites were only 50% bigger than the Skimbat, but the lack of weight counted here as well. They could be steered round in rapid figures of eight, and much of their pulling force was generated by their own movement through the air.

Holding both types of sail felt like trying to hold back a couple of tractors. No wonder that people could go uphill with them, and over bumpy snow. In comparison, the Skimbat felt like a thoroughbred Ferrari firing on only one of twelve cylinders. How I longed for some proper wind !

The brute force worked best downwind. Everybody seemed to take for granted that no beginner, no matter what natural gifts he had, would be able to sail to windward with a kite. When I held the kite and the "Skiseil" against the wind, it was easy to understand why. The highest forces were generated at high angles of attack (AOA). When the sails moved forwards, against the wind, the AOA lessened, and the force decreased. There was a balance point where the dynamic force pulling the sail forward equalled the wind resistance on the sail, pushing it backwards. When I got too close to that point, the control lines would go slack: Zero force and zero control.

It also worked best uphill. For Gert-Jan and me, it was strange to see how the soft sails all seemed to work best against a certain amount of resistance, i.e. in heavy snow and going uphill. For the Skimbat, that's the worst possible conditions.

The big "Up-Ski" circular chutes demonstrated this property in a funny way. At one stage, two competitors were coming up to the finishing line at the same time. Both of them tried to hurry forward, with the inevitable result that both chutes collapsed in a vast tangle of nylon and lines. They were left standing still, panting, looking helplessly at the mess between themselves and the finishing line, until a puff of wind was strong enough to lift the chutes again.

The same phenomenon applied to the "Skiseil" and the Kites. When you have no ground friction / forward resistance, your speed will keep increasing until you obtain an equilibrium. In this state, the forward pull of the sail will equal the air resistance on the skier and on the sail itself. This is perfect for the Skimbat, which is hand held and has an extremely effective wing profile. It is not so good for the "Skiseil" or for most of the Kites. With their (relatively) ineffective wing profiles, they meet a lot of air resistance. If you go too fast with them, they get blown backwards (remember, they're not at arm's length, but out at the end of a vast number of lines), and end up more or less directly to the side of the skier, giving little or no forward pull, compared with the enormous sideways pull on the skier. If you accelerate too fast, you may even get ahead of your sail, and experience a backward pull.

Both "Skiseil" and kites demanded skill and constant attention. The kites needed to be whizzed round the sky, while the "Skiseil" tended to rotate downwards when it got too close to the ground. Obviously, a lot of skill and practice is necessary if you're going to fly them in strong winds or fast to windward. The competition results bore this out: There was often as much as five minutes between the winner and the last participant in each class, over a relatively short course.

"Soft sails" are not only difficult to handle: They can be dangerous. This was confirmed by everybody. These sails are either "up and pulling" or "down". When they're down, it can be difficult to get them up, and it can be just as difficult to get them down when they're up. And as long as they remain "up", they keep pulling. The disadvantage of this can become painfully obvious in strong, turbulent winds.

A Skimbat sailor can, on the other hand, always "neutralize" his sail at a fraction of a second's notice. (And if he lets go, it will not fly far on its own). He can adjust the power of his sail stagelessly, from zero to 100% and back, so it's safe and easy to get the sail both "up" and "down" no matter what the wind is.

All in all, I'm more than ever impressed by the Skimbat, even though the racing conditions at the championship showed it off from its worst possible angle. It is simply in a class of its own, when it comes to

* Simplicity in use = easy learning

* Safety

* Windward ability

* Direct control

Because of this, it can tackle high winds, turbulence and high speeds in a way no soft sail will ever be able to do. In the mountains, it gives an entirely new dimension to the days when other people (with or without sails) go indoors because of bad weather. It all boils down to this wing's vastly superior effectiveness and the superior degree of control of a directly hand-held wing.

These advantages are bought at a price.

* Straight downwind performance depends on sail area. The Skimbat is small, and can't be whizzed about in close figures of eight, so it gets left far behind when running dead before the wind.

* Below 4 m/sec, the Skimbat sailor needs a flat surface and an icy or hard snowy surface in order to move at all. For serious uphill work, it needs 10 m/sec or more. The "Skiseil" and kites need less wind, particularly uphill.

* Below 4 m/sec and on uneven ground, the kites have an enormous advantage by getting a clear wind above the ground effect. (On the other hand, their long lines are vulnerable wherever there are trees).

* And most importantly: The soft sails can be stuffed into a small sack, and carried along "just in case it starts to blow". Only the true enthusiasts will carry a Skimbat along under similar conditions. (I do, but only sometimes).

Conclusion

The soft sails are best for all-round sailing in the mountains, while the Skimbat gives a fantastic "kick", and is just plain addictive on ice. Both sails can be used in the other's "territory", but at a disadvantage.

* Using a soft sail on ice (or on a level plain in good gliding conditions) calls for a bit of skill and a relatively small sail.

* Using a Skimbat in hilly country calls for strong winds. If the wind is strong enough, a soft sail of suitable size will

still have advantages uphill and downwind.

Moss, 2000-04-17

Jørgen Klaveness

www.advimoss.no

jorgen.klaveness@advimoss.no