Kiteboard Theory - Thread 4: Light Wind Boards

Postby James on Tue Aug 07, 2007 3:53 am

For a change, this will be a short, simple post, with a slant toward beginners.

After light-wind sessions, I often meet novice riders who have been struggling to stay upwind in the conditions of the day, and they often want to know "What size is your board?". It's a reasonable question, but one that infers an oversimplification of the issue because the length and width of a board are not necessarily the most important parameters for riding in light wind.

Before getting into those parameters, it's worth pointing out that the three factors that limit light wind performance are generally:
1. Rider skill - most important
2. Board performance - next most important
3. Kite size and performance - least important

Before anyone gets excited about the order of importance that I assigned to boards and kites, let me say this:
You could get upwind in 5 knots of wind or less, even with only a trainer kite, provided that you have the right board for the job, such as one of those big, floaty windsurfer boards with a centreboard.
But conversely, there is no kite that will let you ride upwind on a conventional twin-tip board in those conditions.
So, the board is ultimately more important than the kite for light wind riding.

Now, about those boards:

In simple terms, the flatter a board is, the better it will get going in light wind, and the better it will stay upwind. Size matters too, but a board that has a lot of rocker (curve) along the bottom won't perform well, even if it's big. Rocker is great for control, for carving turns, and for softer landings from jumps, but it is not an efficient shape. A curved bottom is like an upside down airplane wing. It works, but it creates a lot of drag, and not so much lift. When inverted, an airplane's engine has to run at higher power to stay aloft. But when you rely on a kite for power, you can't just open up the throttle.

To get technical, a flatter kiteboard generally has a higher lift/drag ratio than a curvy board, because it creates more lift (which keeps the rider up) and less drag (which slows the rider down). This is critical in lighter conditions, because the power that the kite can produce from the wind is limited. A flatter board is more efficient in high wind too, but it's more difficult to control and not as much fun to ride as a board with more rocker.

Probably the best board for light wind conditions would be a rectangular piece of plywood with a very smooth low-resistance finish on the bottom. I won't get into optimal board "outline", but regardless, it's not as important as the flatness (or the size). Unfortunately, plywood boards tend to be heavy, and being totally flat, they tend to be challenging to ride, even in light wind. A good compromise is a production board like a Spleene "Session" or "Door", which have a very slight amount of rocker for controllability. There are other fairly flat boards as well, including the Slingshot "Glide". Some of the other boards achieve lots of lift by being really wide, which makes them difficult to "edge" when riding, so I am a believer in the boards that aren't quite so wide, but achieve lots of lift by being flatter (like the Spleene boards). Having said all of that, if you race upwind, especially in light wind, you will probably do best with a custom board that is literally as flat as a stiff piece of plywood.

Regarding size, the bigger a board is, the slower you can ride it without sinking, so the better you can go upwind. If this is unclear, read one of my previous threads about "apparent wind". Simply put, the faster you go, the more wind you create, but the wind that you create is not in a useful direction, so it becomes a limiting factor, especially in light wind. With conventional twin-tip boards, there are practical limits for maneuverability when it comes to size. The largest size of "Door" is about 164 cm long and 45 cm wide, and I wouldn't want to go much bigger than that. I find that the light wind limit of the "Door" is only slightly better than the "Session", at about 141 cm x 42 cm.

With "directional" boards (having definite front and back ends like a surfboard), the best light wind performance will be achieved with bigger, flatter, floatier boards. Taken to the extreme, if you ride a board that is big enough to float you even when at rest, then you should be able to ride upwind slowly with any kite that will stay up in the air. Keep in mind, as long as you go slowly enough, the "apparent wind" direction won't compromise your ability to stay upwind.

That's all for now,