I am new to this forum and have spent some time searching and looking through threads for info to help me build my quiver of front foil wings. I'm hoping to get some advice on what size foils I should be using for given wind speeds and sail sizes. To start with, my stats:
I am 198cm tall and 107kg, I have been fin windsurfing for 30+ years. I started wind foiling 2 years ago.
I am an intermediate wind foiler, I can readily pump up on foil and hit about 30% of my gybes on foil.
I have a North Pacific board, 145 liters, 220cm in length, deep Tuttle box.
I currently have a Sabfoil Balz Pro 909 (sabfoil.com/en/products/VBALZ_909-370-903_GLD), with a 1000cm2 front wing and a flat 370 stabilizer. I am using a -0.5 shim on the stabilizer.
In 13-18kt range, 5.2sq/m sail, I feel in control and don't feel like I'm fighting to keep from breaching. But as the wind speed picks up, even with smaller sails, I find myself constantly battling to keep the foil in the water, and end up porpoising, slapping the water or breaching. With a Tuttle box, I can't adjust the mast placement, but I have moved the sail mast forward, which I have currently at 113cm from the front Tuttle bolt.
I know I need smaller front foil wings, but I'd hoping to get some input on what would be a good size range for given wind speeds/sail sizes, to fill out my quiver. I am also considering changing to the Gullwing rear stabilizer, as that is supposed to provide more stability.
Any advice would be appreciated and if I missed an existing thread that covers this topic, feel free to point me to it.

Awalkspoiled said..
I'm shorter but at 105kg of similar weight. I'd suggest that, if you mostly ride the board flat, before investing in a lot of foils you work on how readily you can heel to windward. It reduces the lift of any foil you are using and will probably add 7-8kt to the top of the range of any foil. It works better on higher aspect foils but will work even with the Balz you have. I'm using a Patrik AIO setup now, and don't need to change off my HA 1120 front wing until it's blowing close to 20, although from 16kt up a 900 is less work.

I’m not sure what you mean when you say, “if you mostly ride the board flat”. Do you mean mostly ride flat water? I do spend my winters in Baja, riding ocean swell. I suspect that adding the swell to the mix will push me towards a smaller front wing.

Ah, okay. I am mostly flying horizontal. I’ve noticed the racers flying their boards canted to weather but didn’t realize they did that to handle being overpowered.

Roy said..
I think a lot of porpoising is due to inconsistent sail mast foot pressure - basically you let out your back hand in a gust which drops mast foot pressure and the board lifts - then you start fighting to control it. In these cases you need to lock in and just drive it harder (although can also result in some big catapults😀)

Perhaps before buying more stuff, you try a few things.
- Bringing the mast right back with the smaller sail might help to reduce this variation in mast foot pressure (it will be a little more squirrelly at take-off).
- Moving your foot straps forward
- try using additional shims that reduce the lift
- try using a sail size that you can only just get onto foil with pumping & in a gust (i.e underpowered sail )

Roy brings a list of very good suggestions & "low hanging fruits".
Not everybody does realize that stabilizer shims are not only for optimization for specific wind range (e.g. in SB race foils, silver fuses).
For example Starboard posts a list of windspeeds for each shim for their "standard user" but having "less aggressive lift enforced by stabilizer - lower angle of attack of the front wing" causes that foil accelerates forward instead of upward in the gust.
The extreme example of this effect we found out a hard way with Slingshot when they released i99 (or i84) wing with new 480cm (larger) stabilizer.
Pretty much everybody (including myself) was mounting the stabilizer the same as it was known "winglets up" and we could not push the board out of the water ?!
Then Slingshot released update that 480cm stabilizer should be mounted "winglets down", same as front foil.

Hi, I use the same 909/903K/370 combo and 83cm mast almost exclusively. 12 to 30+ knots. Sail range 5.2m to 2.9m. Severne Predator 110 but I'm about 85kg. Larger sails are Foil Freeks, smaller is Blade and a Combat Pro. All the sails are super easy to switch power on/off. Tend to rig pretty tight leeched unless mad windy.

Been foiling a few seasons, 100% gybes, most 360s, some air time, similar windsurf "career", go for it and let your body dial in the micro movements. I'd say you're on a familiar phase of the learning process 😀👍

The 399/395 stabiliser will add pitch stability over the 370. It does sound like you need smaller sails though. I’m 90 kg and with the 909 I’m using a 3.3 in 20 knots plus.You could try the 808 but at over 100kgs you will find it needs a high board speed to keep it flying, when things go wrong they go wrong quickly!!

From my point of view, foil size is an equilibrium between speed and rider's weight + foot mast pressure and "angle of attack" of main foil. If the wind is strong and you can go fast easily and you can not increase down force and being able to point the board's nose down (to decrease angle of attack, ence foil lift capability) you will inevitable breach. So, don't try to run your foil faster than usual and you are ok. For me it's very usefull a phone app with speed readings on speaker. No mater how strong the wind or big or small the sail try to do not go over 15 knt with your actual foil. If you plan to go faster than that, go for a smaller front wing no mater wind speed or sail size.

Thanks all, very good feedback and advice. This has given me lots of things to work on and consider. At my local sailing sites, there are not a lot of wind foilers, which makes it challenging to get input and advice in realtime. This forum is a big help.

bajafoilguy said..

Roy said..
I think a lot of porpoising is due to inconsistent sail mast foot pressure - basically you let out your back hand in a gust which drops mast foot pressure and the board lifts - then you start fighting to control it. In these cases you need to lock in and just drive it harder (although can also result in some big catapults😀)

Perhaps before buying more stuff, you try a few things.
- Bringing the mast right back with the smaller sail might help to reduce this variation in mast foot pressure (it will be a little more squirrelly at take-off).
- Moving your foot straps forward
- try using additional shims that reduce the lift
- try using a sail size that you can only just get onto foil with pumping & in a gust (i.e underpowered sail )

I agree and have noticed the effect of sheeting out in gusts which results in a change in mast foot pressure resulting in unwanted lift. I am already trying to drive through locked in. I’ve also got my foot straps all the way forward (no back straps), and have been using negative shims. I’ve tried -1.5 degrees, but found that -0.5 to work best. My fuse has -2.3 built into it. I also have been using smaller sails (undersized as you suggest), to test whether I have better control of the foil in stronger wind. As I mentioned, in lighter sub-18kt wind I actually feel good on this foil and can manage nice stable flight. It’s when it gets up into the 20+ range that things get unruly. Which leads me to believe that I maybe pushing too much foil in those conditions. I do hear the advice of don’t be too quick to blame the equipment and not do my due diligence.

Which brings me back to my original question; what wing sizes are people using for a given wind range? I understand that there will be many variables in gear, rider skill and weight, etc. But I am curious to hear if and when you change to smaller foil sizes (mostly front but stabs too) for a given wind range.

Correct me if I am wrong a - shim on a bottom mounted stab like SABFOIL or Slingshot =more lift ?

All that is written here is very familiar and IMO indeed part of the windfoil learning curve.
I ride a Balz 899 1300 cm surface wing all the time and should go to the 799 sooner.
At 85kgs and sailing on choppy flat water(only just venturing into waves and that is indeed a game changer, porpoising all over again) is that for me a large stable wing like the 899 actually helps in 20+ knots if you go really down in sail size. Above 20 knots I would be on 3.7 or 3.5. Like that the speed remains the same as with a 4.7 sail at 16 knots but the gusts become easy to handle.

I sail wave sails all the way but keep them tight leeched with minimal downhaul. 4 battens. In the small sizes I find a softer 3 batten sail to be pure bliss and much easier to handle the gusts than a stiffer more direct sail. I would try smaller sails before reducing the front wing in size.

For me positive shims helpedto keep the pitch more stable in the beginning but you tend to foil out more abruptly and add drag. I have no more shims now and the setup is noticeable faster and less prone to foiling out, but my skill and comfort zone (important) did expand over time.

grtz