I set out 18 months ago to build the lightest foil board in the world.
Prior to this, JUNE 2022, I had ordered a custom downwind board 7’ 8” x 25” @ 130 liters. This was before Kalama and KT had established their more advanced dimensions.
The board ended up: 19 lbs 11 oz WhoooAAAAA!
I was a mechanical design and aerospace engineer in college so I went Ape Sh~t to figure out how much a SUP style foil board should weigh. Someone had posted a custom Kalama 100 liter board that claimed to be 6 lbs. I ran all the numbers and figured out that YES! this could be possible with an EPS core and super thin, light lamination (not sure how to make it waterproof) but OK it could be possible. Then I pinged the guy and he said “Oh I remeasured and it was more like 10 lbs.” But I had figured out how this could be done mathematically.
A few months later my foil amigos Josh and Kyle handed me a blank, made out of XPS. They had soured on the XPS approach, waterproof foam with some history of delaminations. The blank was 7’ 10” x 21.75” x 6” ~ 130 liters and it weighed 6 lbs 14 oz or 3.12 kg. I mapped out how to make the board weigh less than 10 lbs and it ended up 9 lbs 12 oz or 4.4 kg. For comparison sake this ended up being 7.6 lbs / 100 liters. What is known as the HL factor (Hectoliter factor = lbs / 100 liters) to normalize for boards of different volumes. I named it the Sailfish.
It was just HALF the weight of my first downwind board.
190 sessions later I had learned to flat water paddle up, downwind foil and catch many multiples of waves in small clean SUP foil conditions (up to 8 for 1) on the Sailfish.
I then built a 6’ 9” wing board, a 10 foot big wave foil board and learned where I may have gone too far with regards to thin laminations, stress points length and width.
Here is the latest evolution: Orange Crush
The objectives for Orange Crush were:
US East Coast SUP foil board for clean small to big conditions
Open Ocean downwind board for Northern California with mixed up long & short period energy
Results: 8’ 8” x 19” x 6” @ 128.6 liters just 10 lbs 11 oz or 4.9 kg. HL factor = 8.3 lbs / 100 liters.
This ended up among the lightest design structure in the world for any foil board as measured by pounds per 100 liters. When Elon Mush built the first commercial rocket company in history he observed:
“If you’re not adding things back in at least 10% of the time, you’re clearly not deleting enough. . . the bias will be to add things ‘in case’, “but you can make ‘in case’ arguments for so many things.
Estimated CG ended up 1.5” behind Center of Buoyancy aka balance point with tracks
10” Box centered 9.3” behind estimated CG (Note CG did not move after lamination)
Box centered 10.8” behind Center of Buoyancy
Reinforced with 11 Vertical Carbon Arrow shafts deck to deck
2 ½” x 8.9 oz Full length Unidirectional Carbon Stringer Top and Bottom
3 x 5.8 oz Carbon Deck – Triaxial layup 30 / 60 / 90 degree bias
1 layer 3.7 oz S-Glass Bottom
1 layer 2.2 oz Kevlar nose and tail
1 x 1.5” x 3.7 oz S-Glass Strip on Front Rails for paddle protection
I kept a record of all time and materials. Total time was 62.5 hours, Materials cost $460 + $15 for Breather and $10 of Blue Masking Tape + $15 . . call it = $500
Someone asked me “why would you share all this secret sauce?”
Because as my friend Bruce said “Life is too short to be riding crappy foil gear.”
There is nothing like having a light board and the world will be a better place.
As an over 50 year old, weighing 195 lbs I want all the help I can get to flat water paddle up, get up in nasty conditions, pump around in nothing, and/or connect through flat sections in downwind bumps. This is high performance foiling and it is 100% dependent on light weight.
2 years ago you couldn’t buy a downwind board without waiting 9 months. Today the production boards are likely 50% heavier than this design and will cost you $2,500 or more. People are talking millimeters and inches of width (for example), shaving off ounces with bolts and I am suggesting you can go buy some crappy Home Depot Pink Panther foam, make an 8’ x 20" XPS board, use 1 layer of S-Glass, no need to make waterproof, reinforce your deck and boxes and have a 10 to 12 lbs board. This adds to a 20% to 30% improvement.
4 were cored through the top of the box until they butted up against the actual track material. Then 7 more arrows were cored from Deck-to-Deck. Just send them through the entire board and sand them off.
What you are creating is a table platform with Carbon legs. The top deck is a carbon table top and ~ under your back foot. The bottom lamination is 1 sheet of carbon and then the arrows are butted up UNDER the base plate. With this design the load is transferred from Deck to Deck and the tracks DO NOT have to carry any real vertical load since the carbon arrows are carrying nearly all the vertical compression loads. The majority of the load comes from the front of the base plate since the foil is cantilevered FORWARD of the front screws.
The 3rd photo was from another board showing the arrows before they are fully inserted.
Your project is a great inspiration! How important is the S Glas? I find that more difficult to get. Could I just use e Glas and be on the slightly heavier side? How difficult is the use of Kevlar? I only used glass and carbon so far.
I want to build a pretty similar board. I still have some Carbon that would be enough for the board. Do you think I can stay under 6kg with carbon and a thin layer of glass? Thx
@Beasho I wasn’t really convinced that weight mattered that much
Then I realised that maybe because my downwind board is already quite light at 4.5kg/ 9.9lb (7’6x18x?, volume not sure but well under 95L)
I just got one of the new Armstrong Downwind Performance 108L boards, weighed in at 6.5kg 14.3lb and it feels much bigger, almost like a bit of a tank, (8’11x~17), quite surprised how noticeable the extra weight is, especially spread over the longer length. It feels very stable, but the feeling of inertia is pretty real
S-Glass has worked great for our small board building community. When I look at Carbon I now seea bunch of dead weight.
No need for Carbon on a SUP downwind board except for around the box and under feet. Any part that is curved or with potential point loads e.g. rails getting hit by paddle or any tiny pebbles on the ground will cause cracks. And if you are building with XPS you don’t need multiple layers of laminate (except under your feet). Just 1 layer of S-Glass, or Kevlar has worked. The Kevlar has almost no compressive strength. Meaning you need to add a stiffener. I have added 2" Uni-Directional carbon “stringer strips.” The first board I did this to and when I was laying down paddling the board it pinged when hitting micro chops similar to sandwich construction boards.
*"@Beasho I wasn’t really convinced that weight mattered that much . . . * I just got one of the new Armstrong Downwind Performance 108L boards, weighed in at 6.5kg 14.3lb and it feels much bigger, almost like a bit of a tank, (8’11x~17), quite surprised how noticeable the extra weight is"
That Armstrong is 13.2 lbs / 100 liters. The Orange Crush was 8.3 lbs / 100 liters meaning that Armstrong was 57% heavier. Performance and 57% heavier only applies to tanks.
I am not sure what the manufacturers can do.
My first 5 weeks in the US East Coast and I only missed 5 takeoffs with this board. I caught ~ 300 waves and missed 1 out of 60 attempts including flat water, downwind (in bad conditions) and SUP foiling. I am now over 50 and will take all the advantages I can get.
Modern shapes, good technique and light weight all matter. At this point I can not AFFORD to go back to a heavy board. Once you have gone light it would be like putting on a GoFoil Kai gullwing and starting over again.
Super cool build! Sorry if you already said this, but why kevlar on top and s-glass on the bottom? And why did you cut out the glass around the track box on the bottom?
“why kevlar on top and s-glass on the bottom? And why did you cut out the glass around the track box on the bottom?”
Delete the part or process.
“If you’re not adding things back in at least 10% of the time, you’re clearly not deleting enough.” Musk suggests starting lean and building up when and if required, but warns that the bias will be to add things ‘in case’, “but you can make ‘in case’ arguments for so many things.” He goes further, arguing that each requirement or constraint must be accountable to a person, not a department, because you can ask that person about its relevance and purpose, rather than having a requirement that nobody owns and persists for years despite being redundant.“” - 1 of Musk’s 5 Design Principles.
Whether you like Elon or not he is a manufacturing genius.
My original hypothesis was to build a ‘foamie’ foilboard. Keep it light and consider everything but the standing or “Cassette” area sacrificial. The deck is 2.2 oz Kevlar because it was the lightest, toughest material I could find. The deck takes plenty of abuse from the ground primarily and accessory body impacts so toughness and lightness was optimized.
The bottom ended up 3.7 oz S-Glass to provide strength in 1) Tension 2) Compression to prevent buckling and 3) Sandability for smoothness. The Kevlar has shown weakness in compression (minor buckling on Bumblebee), results in a slight burlap or sharkskin texture and does NOT sand well. The S-Glass was slightly thicker. I was able to laminate and gently sand with 220 and 320 grit then spray paint. The finish is ‘fish slick’ but not gloss slick.
No need for the additional 3.7 oz Glass layer over the carbon base → reduced 1+ oz of weight.
This is an amazing read, thanks so much for the info and particulars. I’m planning a board build; do you mind if i ask you a couple of things?
Did the 10” Box centered 10.8" behind the centre of buoyancy work out okay? I was just going to stand over the COB and put the box roughly where my back foot was, but yours is way more accurate.
I was going to reinforce deck and boxes in carbon, the use 2 layers of S Glass top and bottom. Do you reckon that’s sufficient? I’m not trying to build it super light or anything this time.
Thanks so much once again, this is all super helpful
Finding the center of buoyancy is a little tricky.
You want to find the center of buoyancy - but at the weight of yourself plus riding gear plus board plus foil weight but also the foil’s buoyancy, which is by no means negligible unless it is neutrally buoyant. My axis kit is negatively bouyant with that super heavy carbon mast, but some kits are positively buoyant, especially if you’re running a NoLimitz mast for example.
Rider weight will change the waterline depth pretty substantially, which likely shifts the buoyancy center. Usually, a lighter rider weight will shift the center back because less of the nose is engaged.
But most importantly you want the bouyancy center when the track itself is level with the water-line or maybe +1-2deg.
So, if you really care, spend some time figuring this out. But probably it won’t matter much if you’re putting in reasonably long tracks.
For my barracuda, I can paddle it up to speed with my weight about +/-2in forward or back of what I think is ideal. But if I’m too far forward, it pitches down the foil and won’t engage early lift. And if I’m too far back there is too much angle of attack on the foil and a ton of drag through the water.
So then, Ideally we would get the foil in just the right spot on the board so that as it engages lift our feet and weighting don’t have to move at all.
Then we have foil brand variability to mast versus foil placement. And bolt pattern variation - most masts aren’t symmetric forward and back of the mast center-line.
Here’s numbers that are working for me:
12" back from buoyancy center for axis mast with standard fuselage in bigger ART Pro wings
10" back from buoyancy center for axis mast with advanced fuselage or Code foils
Ah, thanks great thanks.
That’s really interesting about the waterline,. I didn’t account for that - if there’s masses of foam say, in the nose, but it’s above the waterline, it’ll affect the centre of mass of the blank, but not the centre of buoyancy so much. That makes it all more complex, but the 10" for the advanced fuse is good to know, thanks
