F4Foils Tuning Tips - Towards 30 knots!

I'm seeking tuning and 'feel' tips to break the 30kt foil speed barrier. I've made the switch to F4 and feel like they definately have the potential for great speeds. After 3 months I have improved speeds from 20 knots to 27 knots as of yesterday. I'm adding my tuning tips here, and am keen for anyone to share there experience.

I typically ride with high boom, long adjustable harness lines and a seat harness (have done for 30+ years). For context, I'm 188cm and weight 80kg. My Foil board is FMX Hyperion 91cm - awesome board!. Some of you may be familiar with it... www.seabreeze.com.au/forums/Windsurfing/Foiling/Foil-board-Repair-Job-The-new-nose-you-all-need

I wrote an F4 Foil review soon after getting my new wings: www.seabreeze.com.au/forums/Windsurfing/Review/F4-Race-and-Slalom-Foil-Sets-2021--Long-Review

560 (700 wide) front with, small 190 rear wing on 90cm short fueslage Mast base 128 (full back!)
This was the setup I used for max speed. I had the mast track all the way back, just in front of the bold hole so about 128cm on my FMX 91 Hyperion. Front straps are in the 2nd front holes and no rear straps.
At first I had the 0.5mm small shim in and my back foot was nearly hagging of the back of the board to control ride hight.
After removing the shim my back foot was over the rear holes of the back straps (I sail without rear straps).
Trim still felt too far forward, occasionly I would dip the nose too easily when sheeting in but felt very balanced and was happy to push more.

On deep downwind runs needed very little downforce to balance the lift and achieve top speeds... probably need to commit more to the harnesss as speed increases but was very light feeling at 27 knot run!
(Compare this to my PB of 28 knots on AFS 800 set where I was bracing for impact fearing death...! But with 2 years less experience!)

I've read some riders on the short small F4 slalom setup actually put a shim in backwards! I'm yet to try this.

81cm board? I've occasionally felt my feet were too far outboard, rotating the heels inwards. Is a narrower board better for top speeds on small wings?

100cm & 115cm fuselage
Other times I've used the 100cm fueslage with mast base at about 133cm felt about the right balance point, probably more nose down taps rather than too high moments. I've used this length more and think I prefer the extra stability (sligthly less responsive).
I tried the 115cm fueslage with the small wing once, brings it further back c.f. the 100 and felt quite good too.

Prefered sail is 5.5 or 6.3. I'm using old slalom sails with a new clew hole mounted just above the long batten.
The 560 is quite a small wing, so needs about 15kts board speed to flly so decent planing speed, and you can get stuck in a lull :(. Responds well to power in the sail and is surprisingly comfortable with a 8m sail when the wind gets lighter!

620 (800 wide) front wing, 190 and 210 cm rear on 100cm fueslage
Definately has more and earlier lift than the small wing, making gybes easier to fly through too. My speeds are about 2kts slower on the same day c.f. the 560 with this wing, but I'm sure it has more potential.

I started riding with the mast at 136cm but quickly moved back to 133cm and reduced shim from 1mm to 0.5mm.
The 100cm fueslage has the wing further forward than the 115 so does need more harness commitment. I haven't tried all fueslage options with this wing yet.

850 (900 wide) front wing, 190 rear on 100cm fueslage
I've spent the least amount of time on the small race wing. I expect it would be really helpful for bottom end slalom racing especially at the gybe marks for a small tradeoff in top speed.

945 (1000) front wing, 210, 230cm rear wings, 115+cm Fueslage
The big course racing wing has a LOT of lift and the power really increases with speed. Takes commitment to ride fast
I need the 1mm shim to control the power of this wing in anything but the lightest winds.
I started with mast base at 138, almost all the way forward in the box, but have brought it back to 135 now.
Top speeds for me are 23kts so far with 9.0 and 10.0, but I've heard it can "easily" do 28!

Ride Feel - Board Setup
To go fast you need to be comfortable. When I started foiling it felt nearly impossible to get enough downforce on the nose. At one point with my Slingshot foil I even tried building some footstrap adapters to bring the straps further forward. Yesterday I rode the F4 @ 27kts with the mast base right at the BACK and felt really balannced, which goes to show setup is everything!.

Tap down
The most significant change I've noticed lately is how to identify when your mast base is too far forward. It is fine to ride and you can fly just fine but what happens as you accelerate is that the downforce from the sail (even without extra from the harness) pushes the nose down and you tap the waves. This unsettles your balance needing back foot pressure, which then risks going to high and either breaching or porpoising.
If this happens, move the mast base back a cm at a time.

Back Foot too far back?
With too much rear wing shim on I noticed that I had to have my back foot a long way back to maintain ride height. Again not a problem sub 20kts but as you accelerate the balance points are too far apart... reduce rear wing shim helped me here.

Ride Feel - Sail Control
Once the board is under control trim is mainly from the feet, which will discuss next, and sail control. The biggest tip I can think of here is that when you are close to breaching or tapping down, your ride dynamics are only off by a few %, so don't over adjust!. Make small adjustments, trying to maintain harness line pressure and use small movements to adjust ride height, then move back half way to where you were.

You can also send the nose down by sheeting IN the back hand, which seems counter intuitive if your about to breach! Don't sheet out too much... ever!

To make small adjustments moving the hips back/forward/inboard/outboard a few centimeters can have the desired effect, but try to remember to keep the harness pressure pretty stable.

For smaller sails at speed, a high boom with long lines seems to be popular. I'm definatly finding it to be helpful, and am happy I've got adjustable lines on most of my booms.

Reaching at speed can require an amazing amount of downforce, Sometimes I think I've had about 70% of my weight through the harness lines a few times, which can hurt with a waist harness, and is why I prefer a seat harness. This is probably too much downforce and is likely a symptom of mast base too far back, but I'd appreciate some tips here!

? How much downforce to you use thorugh your harness, when sending it!?

Ride Feel - Foot Control
The use of foot control for up and down should be pretty obvious (pitch control).
While riding fast, especially through chop, perhaps less obviuos is the importance of roll control!
Unlike slalom on a fin (windward rail up) you will want to keep the windward rail down foiling, to prevent gusts going under the board and launching you! Especially on wide arse boards like mine.
I typically roll the foil more to windward if getting too much lift, and use the back foot to roll the board flatter if I'm riding too low. These movements can be smaller and more subtle than stomping on the back foot to get up.

Out of Control ?
Finally, what do you do if you're out of control? If your harness is set just right, hopefully you can unhook with a quick tilt of the hips. People often say "Don't let go!" and I tend to agree, especially if airborn backwards, you can more easily land on the foils. I've catapulted forward and looked up just as my board - still foiling - came straight at me.

If you have time, stomp on the windward rail, hard, and roll to windward as fast as possible, angling the foil will reduce lift and if you do breach hopefully you fall backwards instead.

PULL DOWN hard and fast on the boom to drop the foil can sometimes work..

WOBBLE BOARD can also help, as changing the foils angle quickly reduces lift.

The biggest problem as far as I have experienced is that when you get out of control I typically sheet out and even then, I don't slow down so the foil still has too much lift, and now I have less downforce.

Accelerate Slowly... avoid rapid acceleration as you may find yourself out-lifted before you know it!

Having great fun pushing for more speed on SB 800/255/95 aiming for 25knots - 30 is beyond me...
I'm finding that only trimming needed at speed is subtle front hand up/down weighting to change mastfoot pressure - anyone else?

Great post, Mr Berowne, it's full of interesting, hard won and useful information. Many thanks for sharing.

Perhaps this experience may help. I'm not measuring speed (yet) so take it with a pinch of salt. ???? just over a year ago I started seriously foiling on Slingshot gear using both front and rear straps after messing around for a few years. I was finally in a location where I could sail 6 days a week in 12-24kts. Foiling paradise ????After 3 months I removed the rear straps from my SS board. The freedom to move my back foot around greatly improved my ability to foil. After 6 mos of no back straps I had worn out my Slingshot gear and upgraded to F4 race foils/ JP 91cm Hydrofoil. The upgrade was great. Lots of fun, many crashes just about air jibing. After another 3mos my progression stalled. I was encouraged by a pro to reinstall the rear straps. This led to another huge step forward. When I'm both straps I'm more stable and faster. Cavets 2strapping, demands better set up since you cannot compensate for a poorly balanced foil by moving the back foot on the fly. So more trips back to the beach to tune. Secondly it can be tricky getting the back foot in and out and I have crashed doing both. Finally, I fear that big catapults are worse in both straps however that has not proven to be the case so far.
Perhaps 2 strapping might help you add a few knots in your quest for 30kts. I have a question. What system do you use to measure your speed/track. Would you recommend it?

philip

Thanks gaviota and leed. I'm thinking of moving front strap back one screw hole and don't think the back strap will be a problem. Last run my back foot was over the back spot anyway.
I remember another run on my starboard gear (probably 800 wing and 105cm fuselage (for sail!). I was happily sending it downwind, moved my back foot in the strap and went from 20kts to 22kts on the same gust.

In terms of body position I try to do speed runs in slalom mode. commit to the harness, legs mostly straight but dynamic, sail sheeted in and cantered over to windward slightly. Moving the harness lines back has helped too.

Not an F4, but I've been trying to get some speed out of my GTR+ on my iSonic 83 (slalom board) with a 6.0m FoilGlide. Top speed so far is 27 knots. video shows a few runs of 24-25 knots in super flat water. Front foot only in the strap and harnessed in with a waist harness.

Nico's brother, Thomas (silvermedal at the olympics) is training over here atm, main advice he gives everyone is highest boom as possible with extra long harness lines to improve stability and control, and it works....
(wish I could try before lockdown to improve my miserable speed...)

945 (1000) front wing, 210, 230cm rear wings, 115+cm Fueslage

"Move the mast base forward when overpowered" they said. Makes sense, but I have a warning, Hell NO!

Interesting update on the Big Race Gear. I rigged the big wing with 210cm rear and small shim, hittting 22.4 which is a new PB on this wing for me. I then hit a half hour lull and changed to the 230cm rear wing with NO SHIM just to see if it would lift better in the light winds. But being an offshore westerly, as soon as I got a few hundred metres off the beach, the wind built to over 20kts gusts.

However, unlike the first time I used this setup it was stable and controllable, as long as I could keep the 10.0 sheeted in! The upwind angles felt intense and controlled, VMG attack mode (just a shame I didn't have a training buddy). Without the shim I was even comfortable sending it downwind, maybe 1kt slower than the 210 rear wing. The back foot especially felt really strong underfoot and the wings responded to roll angle very well.

Then for a comparison, I set the mast forward 1cm to 136. While I could ride like this in stable winds, but the gusts were nearly impossible to control. Pitch response was violent and scary and after a few runs I gave up trying to tame a wild beast. Feeling like a challenge I then set the mast-base further aft, to 134 and again it was sailable but hard to control and got high a few times.

Setting the mast-base back to 135 again, and control returned. I was amazed at how sensitive this big wing was to mast base setting, but super impressed with the performance when setup right. I then did a few downwind gybes and leaning forward over the foil I could feel the balance point easily and carve the board around with a light sail. The sail flip was sublime... Lean into the turn, open early, shift sail outboard, rearwards and flip, drag forward, pop and go... wow just sublime!

In conclusion, the F4 big wing race set is fast, but super sensitive to mast base position!

"Compare this to my PB of 28 knots on AFS 800 set where I was bracing for impact fearing death...! But with 2 years less experience!)"

I would never take the AFS F800/1080 wing that fast, the F700/770 is a much better wing for higher speeds, and the F700S after that.

It needs to be gusting up to 15 knots to hit 28 knot peaks
To hit 30's it needs to be a minimum of 18/20 knots of wind.
From there ( for me) it gets harder to go quicker no matter how much wind. ( 25to 30 knots still only maxing out at 32/33.
All this is in short sharp winter front bullets. Looking forward to some more consistent sea breezes over summer.