Foil tuning 101

I have now listened to the Erik/Mike tuning guide podcast 3 times, each time getting little bits of extra info, but I still have many questions. I’m hoping to that someone here can help put together a real 101 tuning guide, that is pretty general and applicable to ALL foils, if that is possible.

Where I foil it is generally not easy to come in and make changes and the conditions are so different day to day, so working out what does what is quite tricky. I am hoping that some of these questions can help both me and others work out what is good and bad in their set ups.

1- Mast position. Erik/mike discussed this quite a bit, but talking mostly about subtle differences in feel. If we take it to basics. What are pros/cons of having the mast too far forward? When do you know you have gone too far?

2- Tail size. From experience the smaller the tail, the more manoeuvrable, but what are the sacrifices? Does a bigger tail give better pumping? What is the feeling if you go too small with the tail? What is the feeling when you go too big with the tail? Are there other considerations between lower and high aspect tails, or is it mostly area that is important?

3- Tail shimming. What are the effects (pros and cons) if you go too far, both positive and negative, with the shims?

For the moment those seem to be the key tuning details. If there are other things to consider would be great to hear too. Thanks in advance for any help.

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1: Mast forward is less drive, increase in yaw. Mast back is more drive, stiffer in yaw.

2: Large tail, stable, lots for your back foot to push on. Small tail, easier roll rail to rail, less drag.

3: Shim, I think of it as rocker in a board. You can add or take away rocker with how you shim the tail. More shim, more drag. Drag = better turning, which is why thruster’s turn better than twins.

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Haha i was just writing this up when you posted!

Was thinking about this while doing downwind laps yesterday, could someone go through and write up what each adjustment does for the following criteria: speed/glide, front back stability (pitchiness), turning, weight distribution (front foot vs back foot pressure) or perceived lift of foil, pumping

Move mast front or back
Smaller tail/bigger tail
Shim tail(angle more up or down)
Shim mast base plate (front vs rear)
Fuse length behind mast
Fuse length in front of mast

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The way to think of tail shim and tail size is whats the effect of the change after you re-ballance with mast position.

Conventional thinking is more tail down = more lift…better for larger riders right? Wrong

Well once you ballance it with moving the mast back lift is the same, moving the foil back increased all around stability, both foils are working harder so induced drag is higher(slower) and the front wing has to do more work to make up for that down force so stall speed increased ever so slightly. So you have just made the foil slower and made it require a higher speed to stay up…so the opposite of the desired effect.

For the simplest version, tail up (or tail chop - anything to reduce downforce) and mast forward is faster, more efficient, and more responsive. For 90% of us speed and efficiency are king (unless you’re outrunning a powerful point break) so its mostly a question of how much responsiveness can you handle and how much forward room do you have in your tracks. You’ll find you can tune a wing and ride it for a month and with that experience handle a little more responsiveness so you can creep that foil forward and shim the tail up more. The downside of this is you become used to something thats borderline impossible for your buddies and other’s tuning is miserable!

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Pretty much agree with everything you said. I think I would have hated my current setup a year ago. Didn’t have the nuance in balance and footwork needed to ride it. Extra shim is drag, but also a more predictable and deliberate feeling. Less shim is faster, twitchier, with better pump and glide, but at the cost of stability on all axis. Think that is a big reason I’m needing super stiff masts now. You’re getting some of that stability and predictability back through the mast.

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Thanks for all the information from everyone.

2 further question.

1- When people talk of pitchy/pitchiness is this just instability in the pitch plane. That the board is doing the dolphin too much?
2- What tuning can help improve pumping? I have started using small foils and the speed and turning is insane, but at a cost in the pumping, so wondering if there are certain tweaks to tail size, or shim that could help. Seems like mast forward, small tail, no shim would be the most efficient, but then I guess the whole set up gets really nervous, so the difficulty is controlling it well enough that all the pump energy is directed into forward speed. (similar to trying to be efficient with a mast that is too soft?)

Thanks everyone for your input.

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Anyone here tune their tails and mast position substantially different between winging and prone? I had been de-tuning tail angle prone and followed suit winging, but then I noticed that the lack of stabilizing lift from the tail tended to let my front wing (Armstrong HAs) wonder up and down the water column when out in choppier conditions. That lead to more touch downs and breaches. I’ve since gone back to a middle ground of one degree shim, which I think is a 0 degree overall and it seems pretty good. I’m thinking about pushing back into the positive (de-tuned) realm and just really commit to pushing the mast forward to create that front foot pressure.

Kane has supplied the negative shims to push in the opposite direction while winging. I’ve tried them a bit and it definitely allows a more aft mast position and stable high speed range.

(Didn’t mean to try and hijack the thread, sorry OP)

I run the exact same setup between wing and prone, i just move the foil back and fourth from one board to the other. For me, i’d actually want a little bit twitchier ding setup to combat the extra stability of the board weight (the mass dampener) but i can definately see if your riding something really fast how it would get really easy to get over baked winging and it would be worth adding an element of speed control. You definately don’t need the efficency winging.

Love this thread, from what I have read through so far it seems that the more efficient you tune your set-up - the harder it may be to ride (requires more finesse)?
Recently started running a 13R with my Kujira 980 & found it very unforgiving at first (pitchy) but now starting to feel some of it’s magic.

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As a very basic rule, if you wanted to improve pumping performance would you increase or decrease the tail size (assuming everything else is equal). I had the feeling from a few comments that a smaller tail is faster and better pumping, but I tried a few smaller tails and felt like I could sort of push through them, which felt very inefficient. Especially trying higher aspect tail designs. My favourite tail in general has a slightly wider chord, less span, but feels solid when I push against it. Am I missing something? Thanks like always.

This really depends on how good you are at maintaining speed. If you can stay in the speed range a smaller tail will win on efficiency. If you’re bobbling or find yourself in turbulent water than a bit more surface area will help. I’m spending a lot of time on smaller tails with a bit more profile thickness. Kujira 158 is my favorite currently.

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This really depends on how good you

Not very is the best answer!! But what you say makes a lot of sense. When conditions are good its no problem keep speed in the pump, but where I was struggling was like you say in turbulent water, or losing speed getting over whitewater etc, so what you say matches my sensations I guess. Thanks again.

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There’s too much info to outline in a forum post but I have a pretty good write that outlines how I tune foils.

Any feedback is appreciated!

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@KDW I tried to capture some of this in pictures here in the linked post. Do you agree? I like pictures to explain things so that would be my suggestion for your writeup!

I’m going to try draw out each concept (tail/baseplate/etc) as they come up for the sake of my understanding

Reply to @KDW Thanks for that. Has that article been edited more recently, as I am sure I read it 100 times before, and this time seemed to get more information from it. Its possible that I am now at a later stage in foiling and therefore have better understanding. Anyway… thanks for a great article. One of the best descriptions/tuning advice I have found. If you have time for more of those, I am sure they would be very well appreciated!!

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Added to it right before posting! After some recent discoveries with baseplate shimming I felt it would be incomplete without some new info!

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@KDW I have read and re-read and re-re-read this article. Love how you break it down and effectively separate the different variables of mast/shim.
However the whole track forward/flatter tail thing, kind of goes against that, bringing the 2 variables back together.
Interested to hear you take on that.

KD’s guide is the best write-up I’ve seen so far for foil tuning. It’s been my go to reference for tuning for the past year.

However, I set up mast placement in the tracks first, to set up how I like the foil to feel on takeoff, then adjust tail angle later.

I’m glad KD updated his guide for baseplate shimming. I ride a Takuma Kujira 1210 with 1 Takuma baseplate shim (shimmed for nose down/thick part in in the back). When I recently got a Takuma 1095HA, I continued to use the baseplate shim, but I was more likely to stall the 1095 compared to the 1210. When I removed the baseplate shim, the 1095 stalling problem was greatly reduced.

I’ve also had stalling problems when riding a Lift 120 (no baseplate shims). On my next Lift 120 session, I’ll have to try it with the baseplate shimmed for nose up/thick part in the front.

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Hey Kane, thanks for the great foil tuning guide. Do you still use the hold front wing at 25% chord (COL) for balancing the boards COG to COL initially for tuning?

Not long ago we were towing into ferry wake, and at one point there were two of us on ropes while we went fast to try to catch up to one. The other guy was on a lift 120, I was on a 1095 with 178 tail no shims. To my surprise, when maxed out I was leaning back trying to keep the board off the water. I had thought it had something to do with the washout pushing down when the AOA got really small, but the bit in kdw‘s post about “diving at high speed = too little angle[of tail]”, makes me wonder. But I’d always assumed takuma tails had plenty of lift on account of the front foot pressure. And no, I didn’t make it. The board glanced off the water, slowing it just enough to send me flying.

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