Displacement vs planing regime for board shape efficiency in low wind winging

Hi Guys.

Coarsly simplified, in a nutshell:
-in low, displacement speeds, long and slender and fair with no edges is key to reduce viscous and wave drag to be more efficient through the water…(compare low wind region sailboats)
-in higher, planing speeds flat and wide with hard edges is key to plane efficiently on top of the water (sufficient forward thrust needed to get over bow wave…compare e.g. motorboats (sprayrails) or windsurf formula boards…)

Now thinking of pumping onto foil with a wing…at first you are obviously in displacement mode and usually get on foil before actually achieving typical planing speeds. BUT. As you are pumping the board (and foil) you are increasing the dynamic pressure on the bottom significantly, therefore getting to a (semi-)planing mode at lower speeds than the normal planing speed of your board. Hence the need for sharp release edges at least at the tail (transom) and aft rails of the board…
Also, you want a rocker and lengthwise volume distribution to allow to rock the board enough in pitch to activate the foil. For a given volume a transverse cylinder (log) would be the least resistance, a long flat plate laying longitudinally the most. Hence rocker and narrower nose and tail/cutouts/step tail etc…
The magic question seems to be to find the right balance between the three contradicting shape necessities, also taking into account pitch and roll balance and rider controllability…

In a perfect world i’d still study yacht design and have access to a towing tank and time to test different models and shed some light on some of my ideas and then use my snowboard building lab to build them…
In reality for the moment i’ll have to confine myself to trying the few to me available boards and relying on feels just like any other of us…

But at least maybe someone has tried a lot of (weird) shapes and also some of those barracuda shapes or similar for winging though and has some ideas on how they perform there?

Cheers,
Andi

Ps. Thanks Eric, this forum is a great idea…

Fanatic wing board bottom shape, combined with narrowness, is the most efficient hull shape I found. My custom is 5’2 by 20" 70L and it gets going with almost no pull from the wing. Flying with 1000sqcm foils in 8kts became a common occurence.
Have not compared with barracuda shape, but it would have to be compared with similar length right?

https://www.instagram.com/p/CgMFuntIylR/?utm_source=ig_web_copy_link

interesting…unfortunately i cannot open insta at the moment, my browser security settings somehow block it…anyway, 20’’ is rather narrow, is it still stable enough to slog/how much you weigh?

Yeah in theory you’d only change one variable at a time, so same dims and only the shape would be different…unless you shape them yourself it’s hard to get that, also taking into account your own progress in skills…and confirmation bias will kick in anyway, so some variation can still be tried to be interpreted nonetheless;)

i just got an ak phazer 5’3 x 24’’ x 66l, will be interesting to compare it to the appleslice v2 4’11 x 24’’ x 78l and the sunova aviator 4’10 x 23.5 x 60l i got…i feel that around your bodyweight (i’m 73kg) in volume smaller changes in volume have a bigger effect comparatively than when going way below or way above…trying to hone in on that one, hoping the added length will help with efficiency…the sunova is too small (and heavy) for the very variable supergusty conditions we have on our swiss lakes and the appletree feels a quite a bit too boaty…hoping for wind next week, we’ll see

I just bought a used Kalama custom 7’6"x20"x 4 3/4". Dave made this board for himself as a Gorge prone DW board a couple years ago. It has a lot of Barracuda attributes. It is the most beautiful board I have ever touched. Anyway, I took it for a lightwind wing the other day and it was quite eye opening. The wind was 5-12mph. Using a 5m wing, I was able to get up on foil very easily in far less wind than ever. The board only weighs around 6lbs, so once up, it didn’t bother me at all having a board thats 2.5’ longer than I am used to. A lot of the board is behind me anyway. I have been wanting to try a long skinny kinds for years. It seems to me that a good amount of my sessions are in light wind with my Axis 1099. I am stoked to have this light wind weapon to enable me to go in almost nothing. I am interested to see if I can get away from the 5M wing and go smaller. Thanks Dave for being a forward thinker and amazing craftsman. I feel so lucky to have stumbled upon this. Thanks Bruce for selling it to me.

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That’s awesome feedback, the light wind future looks bright! Nice looking board, you must be so stoked

80kgs. I take off on the board straight away like on sinkers (no knee phase), so stability is never a problem, the limiting factor is to pack enough volume in the board without being too thick, otherwise I would go 15 inch wide. I think width of the board is as critical as length, just like downwind boards as we see happening at the moment. I would not go longer than 5’2 though because it gets in the way in the pocket of the wave.

little update, sorry am very busy at the moment…

so doing some very scientifically objectivised testing - basically i went winging haha - i tried the phazer v3 5’3 66l in low and medium winds… i absolutely love it…longer is faster i guess…it feels superefficient through the water compared to the other boards i had, sold the appleslice v2 76l straightaway…as long as there are no waves slowing you down, you can really accellerate it pumping the wind even when you feel very underpowered…also feels way more stable to slog than others of similar volume…highly impressed…

on a sidenote…i also tried the new longer fuse from uni with the kd boomerang tail…he always claimed this setup would lower the low end of the front foil…and i think he might be right there, my technique will probably need further improvements to really hone in on this, but felt i could go from vyper 190 down to the the 170 (which i kindly got as a present from them for waiting for the 190 so long)…

on another sidenote, i also finally tried the north nova lightwind 7m (the lightwind version) i got a while ago and i can highly reccommend as well, very grunty, easy to pump, span feels cmfortably short (especially compared o the f-one 7m cwc), nice hard handles…and surprisingly you really don’t feel the weight at all…it is quite a bit heavier than the f-one but so balanced you don’t feel it…very interesting…wouldn’t have thought…and i really put an emphasis on light gear normally, my brm wings are very light comparatively…

so the search for my perfect setup slows down, i guess i am finally getting closer, after gving in to my foilbrain and stretching my cc too often…i’ll try to contain myself and keep to this setup for a while and work more on technique …maybe the progression 170 though haha…