Foil Trim - how to get the balance right

Technique
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A friend pointed out when I borrowed their big foil that I was too far forward. I moved WAY further back, and suddenly it felt balanced, and much more efficient. I then removed the little bit of tail shim, and it felt very fast, very easy to control, and very easy to pump, and able to go much slower. This surprised me as I felt that moving to the bigger foil it would have been obvious, but because of the huge lift, I was too far forward to compensate when going fast on waves.

This reminded me of the process of trimming an RC plane. To trim a plane, you start with weight too far forward, and then edge it back until the plane becomes hard to control (at the intended typical speed), then nudge it a tiny bit forward again to settle. Ideally once settled, it should fly without any stabiliser input (ie “shim”, but this isn’t fixed on a plane). Any stabiliser input is just unnecessary drag and should be avoided where possible.

If badly trimmed, both the foil and stab are working harder to lift you, and input to overcome this requires more effort. You have less glide. I think probably 95% of foilers including myself regularly are way forward of where they should be for pumping, which explains why they cannot link, why they cannot stay high on mast… Continual foot adjustments are probably the most important skill to develop to enable this.

Keen to hear what others think of this, what tradeoffs, etc.

@KDW as I know this is 100% your domain, would be keen to hear your thoughts. You mentioned that you can calculate the correct shim theoretically (in a podcast), I wonder how that assumes you are trimmed? Does it matter.

**Background reading on trim. **

CG vs lift explained. Afaik you can ignore the mast and board when thinking about this, and just think about the foil and where your weight is in relation. The mast only comes into it when pumping.

RC planes and how to trim

CleanShot 2024-05-12 at 17.11.56@2x
CleanShot 2024-05-12 at 17.11.56@2x2098×1042 289 KB

Note - best L/D important for racing, sink rate for staying on foil for hours

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If badly trimmed, both the foil and stab are working harder to lift you, and input to overcome this requires more effort. You have less glide. I think probably 95% of foilers including myself regularly are way forward of where they should be for pumping, which explains why they cannot link, why they cannot stay high on mast… Continual foot adjustments are probably the most important skill to develop to enable this.

I’m increasingly convinced that this is the most important thing for a beginner foiler to focus on to improve their ability to pump.

And,

I’m 100% convinced that it is the PRIMARY issue preventing most Foil Drive beginners from pumping.

Most foil drivers are standing too far forward when trying to pump.

Standing further back makes the board more efficient, but also you have more leverage over the foil on your back leg, increasing the force lifting the nose up.

It seems that on the FD you need to stand much further forward when motoring, but that shouldn’t change much in terms of where the optimal pump position is.

I see it a lot with the FD beginners where once on foil it is pretty apparent that they stand no chance in pumping because of how far forward they are, and nearly 100% of their energy is going towards just lifting the nose of the board, and nearly nothing goes into driving forward.

If you want evidence of this, watch any professional foil drive influencer when they transition from motor to pumping. They will be riding along on motor mode, and once on foil, they shift their feet backwards.

Eg JC himself, moving it a good 3 inches

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Yup in the Coach Casey Club Module there is specific talk about where to stand when motoring and where to stand when off motor.

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Coming back to this, after a few sessions struggling to get paddle ups on the AFS Ultra 750 in light wind bumps, I did what any sensible person would do and put a strip of grip for my front foot as a reference point.

Turns out my front foot was way too far forward, and shifting forward, for that foil, and this was preventing my paddle pumps from causing the foil to lift.

Properly trimmed, the paddle ups became pretty easy.

I’m certain that poor trim is the root cause of most paddle up and pumping issues.

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The root of the problem for most when pumping is that you’re standing too far forward. This is what all wingers do, because of the big pull of the wing.

FD doesn’t help because you stand even further forward

So in both cases when you pump, you push the nose of the board down, instead of jumping up off the foil.

As Gwen says, the feeling is jumping up, not pushing down.

So get on foil (ideally behind a boat), and keep shifting your feet back until it feels a bit loose and sketchy, that is close to the sweet spot. (you could do this on the wing, but it’s hard to stand in the sweet spot with so much power)

Once that trim is right, slow the boat down, let go and try pump. The foil will feel super firm, and you can start to do the “jump” that Gwen talks about.

This is also the place to stand when you’re gliding downwind, on the FD, wing, etc, as this is also the max efficiency, any further forward and your drag increases like crazy.

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THIS is one of the things I wish there was more discussion of in learning to pump…it’s really clear to me when I move my front foot back where it feels like there is no longer any give when I push down…is that the spot? can we say more about just how firm that feeling should be and how best to dial it in?

Addressing this would be super helpful as that change in that feeling as you move the front foot seems like a very clear indicator…thx

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out of curiosity, what foil are you do this on. I am trying to relate to my own experience between different foils.

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This depends on the foil.

A huge pump foil will feel firm no matter where you stand, almost, and will tolerate you pumping way too far forward.

A small high aspect foil will only feel firm when you are going fast and perfectly trimmed. And will easily drop out of this sweet spot, and won’t tolerate you pumping with your weight forward.

So those are the extremes.

For the average surf foil, the more in the sweet spot of the speed, and the better trimmed, the firmer it will be. When it’s firm, your pumps can project forward more, and you can also do the tap pumps to sustain speed.

In essence, yes.

Remember (as Gwen says), you aren’t pushing down, you’re jumping up. So when it’s firm, you can jump up.

Varies hugely across foils, but as above, pump foil, all the time, almost “too firm”. Like concrete. I remember riding a PNG910 after a year off it, and it felt like it only wanted to go up, not forward. Fast MA like the Silk 850 only feels firm when you’re quite fast, otherwise it’s mushy. HA foils feel very firm once up to speed, but easy to push through, like eggshells, especially if you slow down. Also you can’t jump as easily, you need more finesse.

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Love Gwen’s stuff…

Funny though… I thought that for a bit, but then Gwen’s earlier videos emphasizing the point that you need to drive the nose of the board down to gain speed/momentum so that you can then rise up convinced me otherwise…

I realize that his recent emphasis on the hop is largely about cueing, and doesn’t change the physics at all, but again, I think interpreting the feel of the foil in response to foot position/push could be a helpful part of figuring it all out in the learning process…

Very helpful input on your part…thx…

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You definitely need the drive so it isn’t just a hop. The drive is you loading your legs for the hop and should be forceful and very quickly unloaded. The goal is to keep the board as close to level as possible and push/unweight your legs equally.

When done correctly and at just the slightest nose down angle, you’ll get a burst of forward momentum. That’s when you need to unweight the board and stay as high while gliding as possible. Once the nose is back to the slightest downward angle, the process repeats.

I learned on a progression 200 and it taught me some bad habits that were difficult to correct because the bigger foils will still pump with poor technique. I see guys pumping even bigger foils but struggle in the surf because the wrong technique doesn’t translate to a normal sized prone foil.

The best prone Foiler in my area has a pump that looks effortless, the board basically stays level, and he has a cruising speed almost double what the guys on much bigger foils can achieve. He’s on a very small HA foil. You can equate it to a professional golfer that has a slow effortless swing, but can smack the ball for a mile and it goes perfectly straight.

Pumping has not come easy for me and it’s frustrating when you see people that do it well because of how easy they make it look. I noticed the biggest improvement when I focused on pumping smaller foils so that I could really get a feel for correct angles, timing, and proper technique. My plan now is to prone the smallest Foil that I have and really focus on keeping my speed up, keeping the mast as high as possible, and trying to glide as far as possible between pumps. I don’t need to connect 12 waves or stay up for several minutes, I need to perfect my technique and efficiency. The smaller foil gives instant feedback and punishes improper technique by stalling or just pushing through the water.

When you have good technique and timing, switching to a larger foil feels like cheating…but they’re boring to surf on😂

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Soooo many technique videos and I’d pretty much given up on ever getting it.
This post made all the difference, Matt.
I went straight out after work and now…I have firmness!
Thanks so much!
Formerly Flaccid FoilDrive Guy

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This line of thinking also re-re-re-reiterates what Gwen told me over the course of the 3 lessons I took from him…which all can be summarized as: “move your front foot back”

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Yeah pretty much! I think the essence of this thread lies in the fact that it is semingly not “taught”. Most proficient foilers have intuited this feeling of trim, but possibly haven’t realised how it is generally missed (ignore what competent people say, carefully watch what they do)

Stoked! I’m curious if this is/how much of a genuine unlock! let me know what you manage to achieve :smiley:

Fwiw, better trim also means the foil will handle better, see this nice example of someone perfectly balanced

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Thanks for that Matt. This has been bouncing around in my head thinking about when I had felt the firmness. As has been said, I do not recall anyone else mentioning it this way. ( someone may have and I didnt see it). Definitely want to get out in the water and try some tweaks with this thinking though.

That guy in the video is really smooth and has good flow. Goals.

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Trying to wrap my head around all this… So in the video my front foot would be the planes CG and the planes stabilizer would be my back foot?

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I’ve been searching for an explanation for why my Silk 1050 has a tendency to breach on waves waist high and above, thinking it possibly had something to do with my being “overfoiled” (see my post on it here). Then I came across this post about trim and, together with what I learned about overfoil on the other post, I believe I am closer to finding an explanation to my breaching problem. I’ll try to describe what I think is happening and you let me know what you think.

I am motoring along on foil drive. I get to the crest of the wave and rise up above the motor, so that I am now foiling. My front foot had been forward to counteract the upward force caused by the motor. The moment I rise above the motor, all of that front foot pressure causes me to descend. Rather than move my front foot back, which is what I should do, I unweight my front foot, shifting all of my weight onto my back foot. This does in fact stop my descent, but at the cost of loosing speed. Now I’m slowing down while continuing to ascend. This continues until I stall and come crashing down, as though a trapdoor has opened up under me. To summarize, as I decrease my AOA, I ascend and slow down, and eventually stall. If I am correct about all of this, the solution is proper trim. To put it simply, I need to move my front foot back when the motor comes out of the water. This way I can keep the board level and adjust the pitch (AOA) as needed.

It’s not as though I haven’t thought about this before now. I’ve even heard it straight from Mr. Casey himself in his Talk Back Tuesday sessions, which I highly recommend IF you can reliably get video of yourself. Although the saying may go that, knowing is half the battle, the other half of the battle, actually executing on that knowledge, is proving to be far more challenging. Truth is, I haven’t even got to the point where I feel ready to pump, but this post will certainly help when I do get there. In the mean time it’s been a huge help in terms of my conceptualizing what’s going on.

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Well first of all, having a foil.drive makes the board and foil harder to control.then without, leading to more breaches and falls. Not sure if it’s possible with foil drive. But if I find myself breaching, I will often move my mast back a touch using wingscrews in the water. Because truly the relationship between the foil lift, size of wave and mast position will determine how likely I’m to breach. If I set everything correct I never breach

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I’ve been doing some stabless dock start attempts. That really makes it clear that you can split the pumping action into flying the board in the sinusoidal pattern, and the hop up which you need to do without affecting the pitch.

If you’re standing forward on the board, then most of your weight is on your backfoot. Which means to hop up without changing the pitch you have to do a mostly one-legged jump. That limits the total force you can put down, and limits your endurance by quickly burning out the leg doing all the work.

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You might be foil driving into the wave a little late. Your foil might just be breaching as the wave face starts to curve before you can react. Moving your front foot while the foil is loaded up is hard! It’s much easier to step your back foot up when motoring and then step it back when entering a wave.

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I don’t foil drive but I’ve seen this exact issue happening to fd guys . The problem that I see is they’re not going fast enough when the drive comes out of the water and are in a high aoa situation without enough glide to maintain flight. The good fd guys go across the wave with more speed before pulling the drive up so the foil is at a good glide speed at the start of the wave.

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