i have always been of the opinion that once you have an edge the fins are not relevant for upwind performance. However i recently put smaller fins on my board and have been struggling sometimes with getting upwind.
I know that some of the light wind boards have used small fins - like the glide as they create drag. However looking at the latest in race boards and their upwind performance it seems that massive fins help.
What does the pannel of experts think? should i get some larger fins on my board or just HTFU? Feeling a little lost on this as i've never had an issue getting upwind, and generally don't have a problem but in the last five or so sessions i've struggled to get upwind in 3 of the five.
the upwind lift for dedicated kiting raceboards comes primarily from the fins. the lift for your twintip comes from the edge. edge lift is less efficient than fin lift, but has the advantages of not being susceptible to cavitation, and requiring less leverage to hold it down.
larger twintip fins can add to the directional stability of your board as you edge, and therefore may seem to let you edge harder, but they don't contribute any real upwind hydrodynamic lift.
being more sensitive to board angle and the stall thresholds of board and kite, and more nimble on your feet, will help you get the most efficient edge with smaller fins. the wind strength and angle as well as the water surface are all constantly changing. therefore the speed and upwind angle at which you can kite is constantly changing. the more responsive you are to these changes the smaller the fins you'll need, and the better you'll be able to go upwind.
an analogy from windsurfing:
waveboards have small raked fins (great for turning and low speed changes in angle of attack, but not so efficient in a straight line) and use a bit of "edge" to go upwind, even when fully powered.
in contrast, formula boards (course racing) have deep upright fins (super efficient lift at high speed but vulnerable to cavitation from rapid angle changes at low speeds) and are angled to leeward (the reverse of edging) to optimise lift from the leeward rail and introduce an upward component in the lift from the fin.
some of what the formula board gains in efficiency comes at the expense of unwieldiness and higher skill demands compared to the waveboard. they are two different beasts, and different strategies are needed for optimum windward performance.
keep playing with it, keep your fingers light on the bar, let the kite breathe and you'll be on the way to upwind supremacy, and the perks that come with it.
Yep, can't compete with djdojo's answer!
Just one extra thing though, it's not just fin size that matters, but where the fin is. The course board fins (and a surfboards fins) are under the back foot. This lets you ride the board flat (ie not edging much). If you put the same fin at the back of a twin tip well behind your back foot, and tried to ride it flat, it would immediately turn downwind and you'd have to edge it hard to sail upwind defeating the purpose. Another way of putting is that a fin under your foot is a centreboard, a fin 12 inches behind your foot is a rudder.
How do smaller / larger fins on the tail of a thruster change the characteristics of riding?...
I expect a bit looser more radical turn.....would it change the upwind performance?
