Downwind Board Design

[Rjk]

Trying to find the perfect board for sup foiling downwind. I assume a board you can paddle up in the flat well, translates to a good downwind board.

Removing design as the last 20% (ie tail shape or chines etc) i thought I understood design via the three variables below.

Volume : primarily affects stationary balance. 20L above body weight and the deck is level with the water. Can stand on the board without using paddle to balance. Any less volume and you need to start paddling the moment you’re on your feet to get balance. Doesn’t mean it’s less stable but you’re pre fatigued before you try and paddle up

Length : primarily affects front to back stability. Too short and you’re sinking the nose or tail and falling off. Very fatiguing. Longer boards allow more gradual rocker thus can paddle faster without pushing water. Longer boards harder to manoeuvre.

Width : primarily affects board speed. Narrower = faster. The narrower the board the more the foil becomes the dominant force defining stability. Narrower is much nicer for surfing. Downside is super narrow at constant volume means going thick. More thickness to have to get out of the water to disengage surface tension appears to make it harder.

However my progression across these four boards don’t reflect my original thoughts.

Board 1
6’3” * 27” @ 128L
Stable enough. Slight front to back instability. Floats well. Yawed a lot. Zero chance of flat water paddle up. Could downwind but hit or miss if I would get it up. Had to sprint like you wouldn’t believe and have the stars align for me to time it with a good bump. I would’ve given up the sport if I stayed here.

Board 2
6’5” * 23.5” @ 115L
Stable left to right. A lot of front to back instability. Sunken to my shins if I don’t paddle. Still yaws. Paddled up in the flat first attempt. Could downwind if clean runs. Very fatiguing as a lot of energy spent just trying to stand on it. Have to constantly paddle to keep it going. Still have to sprint to get up but for shorter period. Definitely made downwind fun but still considered not continuing due to the huge effort and unknown of making it

Board 3
7’5” * 20” @133L
Stable enough to stand in ocean. Slight left to right instability as I paddle it up. Zero front to back instability. Can paddle up in the flat and get up in shorter period of time. Board not sunken at all. I thought this was my perfect setup. Super stoked and happy to downwind even in 8knots.

Board 4
6’10” * 20.5” @100L
Fully underwater to my knees. Start paddling and it gets up to water level. Couldn’t notice any more front to back instability or left to right instability. Paddled it up in the flat first and second attempt. Probably the easiest of all paddle ups of the 4 boards. Haven’t tried in the ocean.

So what am I missing? I thought I knew it all and was stoked on board 3 until I tried board 4. Maybe the shorter less volume board is just lighter and easier to get up on foil? Is there diminishing returns with length?

Anyone else have similar experiences?

I’m 110kg with a lot of sup experience as reference

[gregclosier]

There is my feedback regarding dw boards. I’ve been testing 6’4 x 20 - 87L vs 7’6 x 18 - 86L
I tried them both on different conditions, from light dw, strong bay run to tricky open ocean dw. Mostly with Axis art 1099 and 999.

I like the 6’4 better, I would say perfect allround board, it makes the take off easier than a 6’0 and while flying it feels the same as a small board because the mast is more forward so you don’t have too much nose in front of you.

The 7’6 is nice to ride, you don’t even need a good bumps, you just paddle and get up on pretty much anything, then flying it feels like it is the dw Cadillac, super comfortable at high speed, easy to move even on tight short hollow bumps but feels better on big long bumps. The down side is when it gets slow, the board (even it is ultra light and responsive) feels slow and it need more work. I will keep this 7’6 for specific conditions, such as big tricky open ocean dw.

[Rjk]

So your 7’6 is easier to paddle up than your 6’4?

What do you weigh?

Is there a stability difference just standing on the boards? Fore and aft? Are they sinker boards?

[gregclosier]

I’m 75kg.

The 7’6 is super narrow (x18) so not super stable but enough to paddle easy.
I would say both are the same regarding stability. They don’t sink.

[Rjk]

I guess my question is trying to find how to size a board for the rider weight. What do you scale? Definitely not width. Length and volume make sense but to what end?

23L volume over my body weight seamed easy. Then I tried 10L under my body weight and it felt better. I thought it would be absolutely impossible for me to paddle up a board that’s 10L less in the flat water. Made me realise I understand nothing

Obviously it’s also a function of skill but it would be nice to have a rough guideline based on accumulation of everyone’s experiences.

We rate foils based on wing loading kg/cm^2 it would be cool to have a similar tool for boards

[gregclosier]

I think it is too soon, still a lot of experimental things with some who like to share and some who don’t.

[Matt]

@Rjk Do you have any updated thinking on this?

Wondering how likely it is that the production boards are largely just scratching the surface of this.

[Rjk]

I realised that a board designed for easy flat water paddle ups does not equate to easy paddle ups in the ocean.

I think I’ve also realised that volume is super important in order to get tail lift when bumps hit the board.

After making my 7’5*20’’ 130L it was a game changer for me getting up in the ocean. I could get up on demand with an axis 1150 and always have a ball. Unfortunately (or fortunately because that’s what makes foiling fun) I then changed my own goalposts and tried to go smaller foils and lighter wind. Thus making me iterate board design to match.

I then made a 7’8” * 18” @120L however my ego made me completely change my design to sharp boxy rails underneath and a rounded tail. It didn’t make it any easier to paddle up in the flat or ocean although board speed was significantly better.

I went back to my 7’5 for a while until I made an 8’4 * 17.5” @130L. A big improvement in paddle ups and no noticeable downside in length. Front to back stability issues greatly improved. However I think there’s an issue with going too narrow. You lose stability to paddle strong and time your strokes with bumps. I also think narrower board means thicker board so the board has to release from further underwater to engage the foil. That is, I now have to pump 7 inch board out of the water compared to 5 or 6”.

I’m now drawing up a 9’4” by 19” 140L round bottom board. Going wider for stability and also because round bottom loses stability. I think the extra 10L volume will give me the tail lift required to get into small bumps. I’m not sure I need to add a foot in length however I won’t see a downside with what I do.

So to answer your question Matt no I don’t think I know anymore. Just spent a lot of time and patience . Hopefully this latest board will be my last

[Becarefoil]

So for light conditions, its better to have a shorter board to be able to pump easier or a longer board to take off easier?

[Matt]

from the french dw open, can’t really imagine this working tbh

[FoilFondler]

It’s like a swallowtail snowboard, but the reasons that works for powder don’t seem applicable in the water.

[gregclosier]

My last post was oct 2022 and things have changed.

I mostly rode my 7’6 x 18 - 86L (pink) and now I have a 7’7 x 18 - 100L

Riding smaller foils, right now using the Codefoils 860R which is not hard to get going but it is still a small foil.
On easy/lined up/hollow bumps, I don’t really need the longer board but I don’t loose much as it is so narrow it turns really good.
But the longer board makes total sense in tricky open ocean conditions, without a longer board it can be a nightmare to get going.

Now the question is do I need to go even longer ? Where will it stop ?

Is longer than 8’ with rounded bottom is the way to go ?

[gregclosier]

For me riding the Codefoils 860R is real game changer for DW. The main reason is because of the ability to ride at 45° if needed. It seems that 13 aspect ratio front wing does it way easily than other foil because of the extra glide.

[Matt]

James Casey discuss displacement vs planing designs

The Casey Catch Up on the Northern Beaches Downwind Foil Race | with Josh Ku, Zane W and Oskar J

Planing (Sunova, Armstrong):

Displacement (Bullet):

A full displacement board, This is the most interesting board I’ve seen in a while. Apparently pretty tippy but works well.

[jondrums]

For me riding the Codefoils 860R is real game changer for DW. The main reason is because of the ability to ride at 45° if needed. It seems that 13 aspect ratio front wing does it way easily than other foil because of the extra glide.

I don’t really understand this comment @gregclosier - what does it mean " ride at 45° "?

[Tanner.0]

I believe he means 45 degrees from 0; where straight downwind is 0 degrees.

[gregclosier]

Yexactly or mayeb I should have said riding sideways.

[Bonifacio]

Can I throw in another variable (location of wide point)?

Most boards seem to have the wide point centered to well forward of center. Is there any consensus on an optimum point?

[beavis]

Been following this thread while watching DW board design. Trying to get hints from every day riders rather than the pro/sponsored group.

I found some interesting comments from someone making their own boards.
Here is a link to his videos:

Peaceful SUP Foil Surfing | empty lineup

Here is what interested me and he posted this 2 months after the video

"one thing that is never talked about or mentioned with downwind boards in videos or podcasts. How unstable and hard to stand on they are. I actually dont like this board much because of how hard it is to just stand on. But im still glad i made it, so i personally know how it feels for me. I made it on the low end of narrowness (18 inches wide) which for me, is too narrow. Even Standing on it in calm water is a bitch and fatigues me fast. I modified my old sup foilboard that was 6’8 x 24inches wide and made it 7’5 long and its Perfect for me! You people take note Im 6’4 and 195 lbs so i have a high center of gravity and am not a lightweight rider. Everyone is different. Shorter lighter people dont need as much volume compared to larger riders. And conditions are not the same everywhere. I deal with alot of wind, currents and chop on most days. This day was rare. No to very light winds. Always windy here in Texas. Millions of wind turbines in this state

Basically, my opinion is standup foilboards need to be wider and have more volume. Less fatigue, more waves, more opportunity, more fun and on and on."

What made me go find this video was his most recent one talking about his board size. He has no problem popping up his new one for a downwind ride.

Ebb and Flow of Downwind Foiling

And his comments about his new board size
"To me, it feels alot better and easier getting up and especially standing up on it.

I made a barracuda style board. Now it’s hanging from my garage ceiling collecting dust. For me at my weight (195lbs) and height. Its too narrow for me. I struggle just to stand on it long enough to get going. Fatigues me quick and takes away from the sup experience in my opinion. So i took my old Sup foil board that was 6’8 and made it a bit longer. 7’6 now. Its 24 inches wide. I can stand on it with comfort and ease and not balance for my life. For me, This size and width is perfect."

[Bonifacio]

18" wide is really getting narrow. The guy is very tall and certainly that’s a factor. We were discussing this in a nother thread here;

Production Downwind Boards

This is currently I think a fact of downwind it is bloody difficult and a weekend warrior is going to be very disappointed if they expect it to be easy regardless of what they buy (other than a motor ) I have the same general impression, and I’m not even sure that the 25" would be more stable in the conditions that ultimately are all that matter - bumpy offshore. I don’t quite see how length comes into the stability but I definitely felt the 23" board harder work to balance than the 20"…

My personal (but very limited) experience was that one particular 19" board was more stable (off foil) than another 23" board. I’m sure length, bottom shape, mast length and foil span make a big difference.