Hello fellow foil flyers!
I stumbled across this years ago, it is mostly for alu foil info but applicabile to ours and some interesting ideas.
I would credit the author but never found out who wrote this.
Foil “glitching” is also another term that is associated with tuning. Glitching is when the foil will cavitate (loose flight) and cause the rider to crash or create the “suck down” where the board seems like it is stuck on the water. To clear the “suck down” glitch, generally it will immediately clear if you run through the boat’s prop wash. If not, then you probably have a week stuck on the foil.
Tuning may help glitching, or it might make it worse (so then, you would need to keep tuning). Glitching is not an easy thing to fix and requires much trial and error tuning. Tuning in order to fix all glitching is out of scope for this article, mainly because no one has really got it figured out…or at least they aren’t sharing the info at this point. Generally, a nicely tuned foil will not glitch as much, and the glitching you REALLY want to get rid of is during an aggressive cut or during the take-off. These types of glitches are what you really want to fix with tuning! Glitches that occur directly after landing, cutting through wakes, and the “just every once in a while” glitch are a bit more difficult to deal with specifically.
When you tune your foil, it will ride better than ever and it will ride better in ALL water conditions. In other words, a nicely tuned foil will need less dialing in when you go from different lakes, water temps, and water conditions.
How to tune…
To tune a foil, you really only need sandpaper. A file can be used, but mainly that is when you are really trying to change the shape of some part of the foil. For most all tuning, the only thing that is required is to touch up the edges of the wings and t-bar. The reason for this is because most of the parts today are CnC machined, which usually eliminates the need to file out big lumps metal or other major problem spots. If you need to repair a damaged foil, a file, rubber mallet, pliers, etc., might be necessary, but this article will not deal with foil repairs.
A good starting point is to use 220 grit sandpaper. The technique is simple…gently rub back and forth. (Nothing really fancy here) Just be careful not to take too much metal off at one time…be patient. After you get more practice tuning, you can use 80 or 120 grit to hurry up and sand off more metal in shorter period of time, if you wish. The only real caution here is to be patient in the beginning and don’t remove too much material, too fast…until you have a good idea of how to tune.
Where to start…
If you REALLY want to get a good understanding of tuning, it is best to just make one change at a time, then go for a test ride. In other words, never change more than one edge at a time. This is will give you the best education on what each change that you are making actually feels like. Of course, this is time consuming, and don’t worry…after you get tuning figured out, you can pretty much tell just by the touch weather it will do OK. So, when you get better at tuning, you can tune a whole foil, then go test ride it, rather than taking baby steps each time you tune a foil.
The easiest place to start tuning (and least risky) is the trailing edge of the rear wing. Trailing edges are pretty simple…make them sharp. I’m not sure you can actually go too sharp on a trailing edge, in terms of foil performance. The downfall with going too sharp on the trailing edges is that it becomes very easy to cut yourself. Generally the rule of thumb on all trailing edges is to sharpen them, but not to the point of cutting yourself when you press against the trailing edge.
On the trailing edge of the rear wing, start on the bottom side of the wing and use 220 grit to sharpen the bottom side first. The actual profile (or shape) of the trailing edge is less important that the leading edge profile (or shape), but I usually sand more from the bottom on this particular edge. You can flip over to the other side of the trailing edge and finish the sharpening there. Just keep in mind how long you are staying in one spot when you are sanding…the goal is to keep everything even so keep moving at a consistent pace while sanding each edge. Sand about 60% from the bottom side vs the top side.
Anodizing… Don’t worry about the anodizing, it will sand off and you’ll have a bare metal ring around your wings. No problem – it doesn’t cause major tarnish issues and it won’t cause the rest of it to flake off. In the end, the ski will ride much better with the edges anodized, because they are tuned!!
So as you are tuning the edge, you need to keep running your fingers across the edges to get a gauge on how sharp you want it to be. Keep using your fingers to feel all of the edges when you are tuning, because you will eventually build up an awareness of good tuning just by feeling the edges of a foil.
Many times, just a simple sharpening of the trailing edges will make the foil ride smoother and quieter in the water. This is the easiest and quickest bang for the buck, but you shouldn’t stop there!
Next…the leading edge of the rear wing.
Tuning leading edges are trickier than trailing edges. First, you have to pay attention to the sharpness and shape of a leading edge. If you get leading edges too sharp, then the foil may start to “hunt.” This means the foil is either going to go up or down (sharp leading edge of front wing) or side to side (sharp leading edge of the strut), and stick to that direction. It is weird to explain, but the foil seems to be sticky or stubborn in the direction it wants to go…it can’t really find middle ground very easy.
If you get the shape of the leading edge wrong, then you could be directing too much water onto one side of the wing or strut (the strut is just a big vertical wing). So the shape of the leading edge plays an important role in the smoothness of the ride.
For the leading edge of the rear wing, here is a little secret to help get some nice “pop” out of the ski. “Pop” is generally referred to as the force of a jump or the foil’s exit from the water. When dip and jump a ski, the force/speed at which you feel the foil take-off out of the water is “pop.” Good “pop” usually means you are going to get more air, so most of the time, people want good “pop” from their foil. If the foil doesn’t have good pop, then people generally refer to it as “dead” or “no pop.”
With the leading edge of the rear wing, start sanding from the top side. You want the shape of the leading edge of the rear wing to direct more water over the top of the wing. In other words, think of the leading edge of the rear wing as digging down into the water more. This will actually give the ski more lift, because as the leading edge of the rear wing forces itself down, it will pitch the nose up. This changes the angle of attack of the front wing to force more water below the wing and create more lift.
How sharp do you make the leading edge of the rear wing? I have found that when you go sharper on this edge, the pop starts to increase, even without the negative effect of hunting. What happens is that the rear wing really starts to catch and react better when you do your dip and jump because of the sharp leading edge. It starts to work in your favor during the take-offs, because it will help increase the steepness of the take-off without sacrificing stability in the cuts or landings. So in general, about 80% of the sanding from the top side and 20% from the bottom side.
On to the front wing…
Now that you’ve built up some skills tuning the rear wing (least risky part to tune), it is time for the front wing. This will usually make a decent difference in how the foil rides. A majority of how a foil rides and feels is determined by the front wing.
The trailing edge is basically the same concept as the rear wing, except you sand from the top down a bit more than the bottom up. Again, it is about 60-70% percent from the top and the rest from the bottom to sharpen it up…go sharp, but don’t get it to the point of cutting your finger when you press or rub against it.
Tuning the leading edge of the front wing Sky Ski wing is probably one of the biggest improvements you can make on the foil. Sky Ski’s front wing, leading edge shape usually diverts too much water over the top of the wing. (This is one of the big culprits in the LE38 flying complaints.)
I’m going to steal some great pictures drawn up by Keith Barnes to help illustrate the shape of the leading edge of the front wing…Keith’s artistic abilities on the computer are unparalleled.
The top wing profile shows the basic stock Sky Ski leading edge (ignore the lengths of the foil…not drawn to scale…lol.) The bottom wing profile shows the overall goal of how you want to shape the leading edge. You will be sanding the leading edge of the front wing from the bottom up 80% and from the top down about 20%.
How sharp? This one is best done via trial and error, until you get a feel for the sharpness by just touching. Basically, you sharpen the leading edge of the front wing until it just starts to “hunt.” After that, just barely dull the edge with the 220 grit sandpaper and re-test. Keep doing this until the foil starts to feel really smooth flowing through the water.
Once you get your leading edge tuned up right, you’ll never let another small ding stay on that edge ever again! Keep that front wing leading edge perfect and you’ll have a smooth running foil!!
Final tuning…the strut
The strut will take the longest to tune (most surface area), but you will actually do the least amount of tuning to it. The trailing edge on the strut is the same as the others…just sharpen it up, but don’t go so sharp that you cut yourself to the touch. Pay CLOSE attention to your sanding technique, so you don’t remove more metal from one side than the other. Make sure to maintain the perfect 50-50 profile on the trailing edge, because you don’t want water flowing faster on one side of the strut than the other. That will cause the foil to pull to one side. Take your time when sharpening up the trailing edge of the strut. There is nothing really fancy about tuning the strut, just keep it even.
When the edge feels good, go ride it. Don’t worry about the leading edge of the strut for now.
If the foil is riding better than anything you ever ridden before, stop there and don’t mess with the leading edge of the t-bar. If you still think it could ride better, or just want to experiment, then do the same thing to the leading edge of the strut. Sharpen it a little bit, but make sure it is a perfect 50-50 profile. Remember if you go too sharp here, you could cause the strut to hunt on the cut and may even increase the possibility of cavitation on an aggressive cut. The trailing edge should be sharper than the leading edge.
Now that the foil is riding its best, you can work with finer grit sandpaper (600, 1000, 1500 – usually wet) and then polish out any scratch marks the tuning has left behind. Remember not to change the profile of the edges when wet sanding and polishing the scratch marks out!
I do not take credit for this, simply passing it along as I feel it fits in well on this post.