Tuning Myths

• Tuning a foil is difficult and requires great skill or special tools
• I will totally trash my the foil if I try to tune it myself
• It is too difficult to tune foils because of all the different water types/temps/conditions/rider size & weight
• Sky Ski foils don’t need tuning

Before tuning, you need to understand how to “dial in” your foil.  These concepts are very basic and deal with setting the proper amount of lift and the proper amount of quickness.  You do not need to change the physical characteristics of your foil to dial it in.  The two main parts to dialing-in your ski are as follows:

1)      Sliding the wings closer or farther apart to adjust for different quickness.  Quickness is how to describe the reaction time of up/down movements in the foil.  If the ski has too much quickness, then it will generally porpoise and be too tough to control when flying or landing.

2)      Changing the angle of the rear wing in order to adjust for lift.  Lift is how to describe how much upward push that the foil has.  If a foil has too much lift when flying, you will need to apply a bunch of foot pressure and lean way forward to keep the ski from popping out of the water on its own.

When learning to get your foil dialed in, you are really starting to figure out your own preference on how the foil should ride based on your riding style.  Dialing in a foil usually becomes a necessary step for people when you begin to move into the intermediate stages of foiling (inverts and starting combos).

So before moving on to tuning, you really need to be able to ride four or five different ski in a row and be able to tell exactly what needs to be done, in terms of lift and quickness.  You should be able to make two or three cuts into the flats, then determine the type of rear wing shim to correct the lift and how much to slide the rear wing for the quickness adjustment.  Until then, tuning your own foil isn’t recommended (generally).

Tuning the foil really starts to become important during the late intermediate and advanced stages of foiling.  When you tune a foil, you are changing the physical characteristics of the foil by removing material from the wings and t-bar.  The main reasons for a nicely tuned foil in the later stages of foiling is because riders begin to really charge into their tricks with more aggressive cuts.  These cuts needs to solid and smooth or else a nasty crash could be involved (28mph + hard cut).  If the foil is not allowing for a smooth approach, then this will compromise the aggressiveness exerted by the rider due to lack of confidence in the ski/fear of being out of control.

Another quality of a nicely tuned foils is the ability for it to “clean up” after landings.  “Clean up” is when all of the cavitation (air pockets) created from re-entry (landing) are cleared from the foil and the foil regains flight.  A foil that cleans up poorly will bounce the board on the water 2, 3, or 4 times after reentry.  A foil that cleans up good will bounce generally only need to 1 time on the water maximum after re-entry (assuming you aren’t loosing too much speed on the landing).  If a foil is consistently cleaning up before the board touches the water, that is usually known as a good quality for a foil.

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.

What about the winglets?

The factory Sky Ski winglets are usually pretty dull.  The winglets provide some functionality by stabilizing the foil and keeping it from sliding out sideways so easily.  Along with this, it is theorized that the winglets contribute to some of the glitching and cavitation issues.  I’ve had some success with noise, cavitation, and less drag by sharpening the winglets.  Also, there have been some improvements in the winglet designs in the 03 Front batwing, 06 Front mini-bat wing, etc.

Generally, include the trailing edge of the winglet along with how you are sanding the rest of the trailing edge (all the way down the curve to the backside-bottom of the winglet.  On the leading edge, stop sanding where winglet starts to curve downward--You want to sand up to the middle of the curve.  The downward portion of the winglet needs to be sanded 50% on each side to make a point.  You want to treat the winglet as if it was the leading edges of the strut, i.e. you don’t want to direct water any faster over one side than the other.  This area is still under experimentation and some hobbyists have expressed really good ideas and results from different winglet shapes and tuning.  At this time, keep it simple and just sharpen them up a bit as described above.

Now you have a tuned rear wing.  You should be able to take your newly tuned rear wing and notice a difference in the ride.  You’ll probably get a bit more lift from the wing, but probably not enough to remove a shim.  You should notice a slightly better pop, since take-off response will have increased with the sharper leading edge.  Also, if the rear wing was generating any noise or drag, it will be gone now…

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!!

Front Wing Winglets…

The concept is generally the same as the rear wing winglets.  On the front wing, I prefer to sharpen the winglet curve area more than the rest of the leading edge.  As the winglet transition occurs, the top area of the wing can start to build resistance and small bits cavitation.  This is a big source of the LEX and LE38 whistle.  I usually experiment with keeping the following areas a bit sharper than the rest of leading edge…(See picture)

When I say really sharp, I mean a little less than the trailing edge sharpness.  If it doesn’t work out for you, then dulling it back a bit is no big deal.  Remember to keep the vertical winglet areas 50% from each side and stay as even as possible in your sanding technique on each side.  If you are uneven, the ski will start to pull to one side or the other.  If you let go of the rope and glide, it should hold a straight line.

Now the foil ride should be working out really nicely for you.  There should be increased lift (maybe you can go down a shim size)...there should be a lot less, if any, noise when flying…An aggressive cut out into the flats should be really smooth, steady, and predictable…with plenty of pressure building at your feet right before the dip so you can kick it like a springboard.


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.

Finishing Up…

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!

Also, after polishing or cleaning the foil, the first part of your run might be a little bit more glitchy than normal.  This is typical after a fresh foil polish…give it a run before making conclusions.

If your foil rides worse than when you started (highly unlikely), then you can just send it to someone and pay them to tune it for you.  You aren’t going to trash the foil by experimenting on tuning the edges.