BWD, that’s on the money info, the crashes from the greater mast heights were spectacularly dangerous and once a lateral foil ventilates its gone. There is a place for lateral area but not as the only area.
Mr Mik, I made a lot of multi foils from 2011 to 2015 trying to get get it to do exactly as you said.
Riding multi foils spreads the lift and allows the foil to have more lift at slower speed and less at higher speed as it lifts.
Here’s one that I and other people have ridden a few years ago . 23 X 16 & Total horizontal area of 211 sq in divided into 3 foils. At speed and due to the curve in the face of a tube, it rides on a single side foil of only 60 sq in.
Multi foils are able to handle the increase in speed and lift really well with the right sized foils in place. The problem with multi level foils was in construction, weight, cost and simplicity. Technology always heads towards removing the extraneous, cutting back the frills so I moved to flat plate Perimeter ( donut) foils. and found that most of your surfing is done in a small range of speeds.
Sure there’s a massive acdeleration When you take the drop and with snaps and stalls, but foiling is initially more about gliding and that’s within a limited range so you can use just a single area foil.
A Single multi foil is still limited in performance and you would want to get the best from a range of waves and you would get better overall performance from A Range of Specialist multi foils than from a sole multi foil design focussed on averages.
So yes a multi level foil has benefits, but make a range to suit a range of waves.
The function of the foil is paramount. Irrespective of what board or struts you use, its the foil that controls the ride. So with intelligent design you get useful function.
If you design a stable foil then you’re only riding the wave, which is what you want to do…why spend an impressive amount of brainpower trying to stay level and in control when it’s just a matter of smart design that will make the experience a constant joy.
So many great ideas from all of you, I should have shared this idea sooner !
I always misunderstood that foil when I previously saw it. I thought the middle part gets screwed to the board, but it’s a foil and the struts are not shown.
Thanks for sharing all this! I’m just ‘mindsurfing’ along at this point, still stuck with fin making.
It’s interesting that they’ll use multiple masts and the wider footprint for the sit-down versions but they still stick with the single mast for “surfing” versions. They’re not seeing anything in between.
The canard layout and distribution of the surface area on this boxed version is different - and shorter - than the “conventional” versions but it’s less than your “donut” and it has no planing surface between the front and rear wings. Obviously built to plane and turn differently.
I’m so slammed with work I haven’t gotten a chance to finish my box installs, but… soon. I’m already thinking about shorter struts and longer wings with donuts.
All the front/ back versions are designed for foiling completely submerged. If either wing ventilates they drop because they need both for lift and balance. But surfing waves with a foil is a different environment because of the steep face so I’ve made mine with the planing area distributed all around the foil, no matter how steep the face or hard the bottom turn there’s always enough lifting area. It’s a lot like the distribution of area on a surfboard and not surprising really. If you had to choose something that would give you similar balance and control to a surfboard you’d probably pick something that looks like a surfboard.
There is something to keep in mind if you decide to do a canard type setup.
If you look at SGO,s foil that snapped at the front, he says that he didn’t hit anything, and he didn’t.
What happened was at a high speed as the nose of his board made contact with the surface causing the board to want to change directions (stay on the surface), the foil wanted to keep going in the same direction (slightly downward), this caused the entire rig (but mostly the foil forward of the mast)to flex and open up, that caused a scoop effect that only increased the force until the rig stopped, or in this case something broke.
I had a beautiful full carbon foil ripped off of the base because of this effect, it had happened a few times before I lost the foils so I was able to understand what happened better when it finally broke.I’d be riding along and all of a sudden it was like someone put on an emergency brake and the board would just stop.But the design of that particular foil was way more susceptible to it because it was an arch between two masts.So as the negative force hit it it inverted which REALLY made a nice scoop.
Putting lifting surfaces (but mostly steering surfaces) in front of the mast(s)s will require extra stiff torsional reinforcement because as you transition from left to right any flex that is in your entire set up will translate into either a high speed oscillation or a foil that wont track straight, it will keep wanting to go either left or right.
I prefer to drag most of the foil behind the mast to avoid this now.
This doesn’t mean that a canard style isn’t a good idea just food for thought.
foil number 2.
Well Wooddave has explained the destruction of foil number one, and the sudden stop experienced.
So version two is an inch bigger at 26" X 17" glass on both sides and some colour,
and the board is bigger too, 8’ x 23", hopefully to allow waves to be caught easier than the last version.
Just need to wait on the right conditions.
Didn’t realise you’re on the same continent.
The larger the foil area the lower the speed it needs to lift but the greater the increase in lift as the speed increases so this could be the perfect foil for you. Once you get lift with that foil you can take out the centre so it works with bigger waves but you won’t need anything over waist high. It’s a fast ride.
Funny that when I started everyone said Nah, won’t work because it wasn’t a NACA foiled wing setup. But WoodDave and the French guy with the box foil all prove that a foil can be almost any shape. Everything seems to work.
I’m mixing theories now doing a split design with part of the foil foiled for slow speed and another area flat plate for higher speed but I dig how you’re customising and making it look professional and Dave’s are more organic in design and the French box foil looks like a folding chair. Such diversity in design.
I used 8.5" Bahne boxes, rears spread at 12" and the fronts at 10". My masts are 8". As I say, I used a 1/8" G-10 spine sandwiched with 1/8" aircraft play on each side. The G-10 is very rigid and holds a screw really well.
Gotta tune the caster on the right rear strut (it’s about 1/8" out of square) and put some more finish on the wing but my setup is otherwise done.
Long time away from Sways but this really caught my eye. Attached pictures of a foil I made about 15 years ago. NACA section. | Glassed it to a 7’ board and towed behind a boat to see how much life it generated. Extraordinary! But being short in the chord the for and aft stability was hard to control when being towed. Never gave it another thought, cut it off and used the board again. Dammit, am now going to have to give it another shot in small surf and see how it works. Now, what did I do with that 7 footer?
Long time away from Sways but this really caught my eye. Attached pictures of a foil I made about 15 years ago. NACA section. | Glassed it to a 7’ board and towed behind a boat to see how much life it generated. Extraordinary! But being short in the chord the for and aft stability was hard to control when being towed. Never gave it another thought, cut it off and used the board again. Dammit, am now going to have to give it another shot in small surf and see how it works. Now, what did I do with that 7 footer?
Cool, your foil profile looks similar to ones that claim to work for SUP now.
Throw a 22-30" fuselage on that with a stabilizer wing and you should be there. Longer fuselage = more control. Shorter = more lively.
Build it so you can adjust the angle of the stabilizer in 1 degree increments with thin washers under the screws holding it on.
Start with difference in angle between the stab and wing at 2-3 degrees.
Make the stabilizer about 25-30% of the area of the big wing.
The Double Foil setup is straight from Orville’ and Wilbur’s designs.
There’s the large front foil that lifts because of the high foil, camber and high aspect.
Then there’s a rear foil that’s angled down to keep the front foil aiming up but it also slows the speed of the foil because it’s creating drag.
And then the rider gets on to push the nose down and balance the up/down of the 2 foils.
So one foil up , one foil down and the the rider adding up nd down as the two foils fight in different parts of the wave.
I’ll explain “ in different parts of the wave”.
Even if you have two identical foils travelling behind one another, each foil occupies a different space, each foil will travel through water that has a different angle of water flow affecting it.
If it was a plane, air is a lot thinner than water and the air currents are larger in scale but on a wave the front foil enters into flow that could be from the side , rising, frothy, swirling, pulling down over a boil or all of these in different amounts and angles because it’s a swirling maelstrom of currents and eddies throughout the volume of a wave.
The following foil , especially if it’s a smaller foil has to quickly fly through the flow that’s just been redirected by the front foil, there’s a changed flow direction, aeration, dead water and so many things are different that would affect the lift and stability of the following foil.
High aspect foils are much like a fluttering Venetian blind where the angle is critical for stability. Combining 2 wings into one is like a bi-plane becoming a delta wing jet.
Now a single foil is going to travel through all the same flow variations as the twin foil but it’s performance is going to be an average of all the forces, a single response from a single foil. And it is smoother and more stable.
A single foil is easier to ride and control, simpler to position and adjust. And they work on kite foils, sup, surf, wake.
A single foil is dedicated to just lift consistently, it doesnt have a second foil that’s designed to dig in and slow the foil speed.
IA single foil has no parts to fit or screw together, that could be injection molded for a few bux that would invite custom foil shaping from a basic shape like any fin.
I believe the current foil makers will eventually catch up and move to a single foil design. It’s just evolution.
