Downwind Board Design

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

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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.

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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?

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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.

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

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

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