Thanks for the replies.

Dachopper. Yes I am going for a permanent connection of mast and fuselage. But I think I will make my wings detachable next time round.

Good info!

I embedded two of these in the bottom of my mast with kevlar tape run through the eye and back up the mast, no problems so far. The mast is moulded, 5 layers of carbon and a layer of heavy S glass with a foam core. Screws pass through the fuselage into the ring nut threads, the connection is quite rigid and there is no chance of the ring nuts pulling out or spinning.

Check out the wing breach then resulting cavitation at 17 secs. Is this standard for high speed breaches or to I need to improve my wing shapes?

That footage is interesting, my question is, have you gone much faster than that without cavitation? If you have ridden faster without cavitation, then I think your shape is OK as long as you don't ventilate the foil, and it's more likely about the ability of the foil to shed the aeration, than causing the aeration in the first place.

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dachopper said..
That footage is interesting, my question is, have you gone much faster than that without cavitation? If you have ridden faster without cavitation, then I think your shape is OK as long as you don't ventilate the foil, and it's more likely about the ability of the foil to shed the aeration, than causing the aeration in the first place.

The run back to the beach in the vid is probably 20% faster. No cavitation unless theres a breach by the look of it.

The question is then. How do design the wind to shed the aeration? my gut tells me maybe a Thinner profile wing tip?

I'm am also thinking the wind size is too big for the silly powered conditions i'm riding in.

I think you just need to practice. Foil can be improved upon after you ride it for a while and really understand the feel of riding. It is so subtle. Later you can improve them for speed. Your music really needs work. Was never a fan of disco porn.

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dafish said..
I think you just need to practice. Foil can be improved upon after you ride it for a while and really understand the feel of riding. It is so subtle. Later you can improve them for speed. Your music really needs work. Was never a fan of disco porn.

That is a fair call. As I am the first foiler locally. Never foiled before and made my foil without any actual foiling experience or have any other foils to look at and and compare against locally. I don't know if the challenge i am having is normal learning, normal foil behaviour or incorrect set up, or bad design.

Re the music. It made me laugh. I certainly to have salt balls in the video!

Thinner, and you can scallop the trailing edge like a whale's side fun.

chevaliertaglang.blogspot.com/2015/07/rambler-88-and-humpback-whale.html?m=1

Looking at that video it appears it is more a problem with the wing recovering laminar flow after the ventilation.
If you could react quick enough to get it back deep it could recover.
Some thicker profiles that in effect move more water, need water pressure to maintain laminar flow so being close to surface could be a problem.
You certainly have a song coming from that foil
Mine gets a bit when nosing down at speed, which I attribute to the changed AoA. Maybe look at that area for an answer.

Looks normal to me. The tip pierced the surface and bubble just sat there. You might have been able to ride it out, if you changed speed or angle of the mast or attack. If you look at my last video, there's lot of bubbles going on and while IIRC they all spit me off, they don't now. Even completely breaching the wing, I usually just ride it out...

Remember, the water is less dense closer to the surface, even though the difference may only be a half meter, you'll feel it. Less dense water is bad for lift and all the other things...

You'll get get used to that sort of thing.

Is that foil singing or is it just coming through the camera mount?

Chef is good too.

Looks normal to me. What length is your mast ? Guys now going to 110cm now, -allows more lean angle and thus can carry more power. It clearly works however !! This is a pic of the Miles Lab foil ridden by Rikki Leccese and Nico Parlier - not the best angle but in the flesh the curative of the trailing edge on the front wing as it approached the mast is really pronounced. The fastest foil at the moment seems to be the Banga Foil however which is very similar in shape to KFA Mako - very straight wings with minimal scalloping.

Nothing thing you might consider is the quality and cleanliness of the finish. Rikki Leccese explained that they clean they foils with rubbing alcohol to remove fingerprints and grease & so on, and they can't just clean 1 spot without doing the whole thing. It then takes 20 minutes or so next session for the feeling and perfume to return to who they like it. I thought he was kidding but they don't even touch their kit with bare hands.....

I guess any imperfections, now matter how small, can have a large effect the faster you go. The top guys are now approaching 40 knots downwind.

Interesting how everybody has different ideas. I wonder who is right? Mast is 90cm James. In hindsight I agree it should be longer for my local conditions. Note this vid is on the most mild least chop/swell day I had foiled on.

Ps I'm not chancing max speed on this foil. I want to get into the waves and carving.

Kamizuka. Water density cannot change unless its physically aerated with whitewash. Liquids are non compressible. The density remains the same. Perhaps you are talking about pressure? Dive the mast down and the increase in head pressure kills the cavitation.

The cavitation is caused normally by a higher rate of acceleration of the water, as this alters the water pressure , which affects density. - eventually causing the water to vaporize. .. but if you ventilate artificially first, u in effect change the shape of the flow around the foil be the fact that there already is air in the mix, which changes the normal flow and can attach itself effectively. Slowing down or going deeper can help shed. Or you design the foil to be hypercavitational and cruise around collecting at 50 kts

On a side note. This was the first session on my 12 chrono. Wind when i launched was sub 10. then when i got into the water it had jacked up to 12-15.

As soon as i got the board out of the water the apparent would kick in and the chrono would CRANK. I was going warp factor 9, powered to all hell. It was real hard to shut the speed down. Edge hard ment more speed...

Lifting the chrono towards the zenith unweighted me from the board and i'd simply fly off the board. Holding the kite low was stupid speed.

I ended up doing a broad reach running towards the kite a bit to kill the power.

It was also the flatest least chop/swell chop conditions I have foiled in too.
So I guess this video is not usual speed or kite or conditions for me.

How good are foil kites and hydrofoils - it's a perfect match !!!

When you are experienced you will find by keeping the kite low and powered, you can ride DEEP downwind at scary fast speeds. In fact you can generate so much apparent that you are basically riding upwind, downwind. 3-4x windspeed is totally achievable.

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jamesperth said..

The front and back wing looks pretty much on the same horizontal level to me...

What happened with the idea of having a back wing above the front one? No back fin? Depreciated as well? Hmm....

You're right, pressure not density. Derp. But water density changes with temperature, not aeration, so while the whitewash may have a lower average density, the water therein is the same.

Cavitation is voids i the fluid caused by low pressure, so if you're sucking down a bubble of air from the surface by piercing it with a wingtip, that's ventilation. AFAIK

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dbabicwa said..

The front and back wing looks pretty much on the same horizontal level to me...

What happened with the idea of having a back wing above the front one? No back fin? Depreciated as well? Hmm....

Above, below, I don't think rear wing placement matters too much, and neither do back fins unless you've got horrific yaw stability issues or really like it locked in on rails.

No updates guys - any more gouge?

I'm trialing a new method to mount the fuselage to the mast - using titanium barrel nuts ;)

So far looks promising

Show a us a pick of your TI barrel nuts. Where did you get them from?

I've slapped some home made foot straps on my mutant


After a but over 2 months in i'm going quite well. upwind, downwind, s turns toeside (on my good side) getting into jumps now (thus the straps). I'm failing at jybes but getting closer. I'm edging into waves now too.

The foil is working well. After changing up to 3.5 deg aoa and studying and understanding the ventilation/cavitation after breaches I've adjusted my technique to suit and getting good performance without random crashes.

Over all i'm super happy with my build. Its doing exactly what i hoped it would do and appears to be on par with commercial units.

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dachopper said..
No updates guys - any more gouge?

I'm trialing a new method to mount the fuselage to the mast - using titanium barrel nuts ;)

So far looks promising

My J Shapes mast has stainless barrel nuts at each end. The top is deep tuttle and the end in the fuselage is normal tuttle. Two 4mm stainless screws lock it in at both ends. Seems to stand up fine to normal riding, jumping and the odd bump into the sandy bottom.

Plummet, when you put the hammer down, do you have to shift your weight forward or rearward to go faster and keep the thing down, near Max speed ?

I made the barrel nuts myself from Titanium rod. Still needs a file to match made profile.....cnc machine might get finished in Jan, I have some good ideas for that

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dachopper said..
Plummet, when you put the hammer down, do you have to shift your weight forward or rearward to go faster and keep the thing down, near Max speed ?

I made the barrel nuts myself from Titanium rod. Still needs a file to match made profile.....cnc machine might get finished in Jan, I have some good ideas for that

Cool. I don't have TI threading capability!

Yeah more weight on the front for speed high speed. But to be fair I can't go too fast because of my lumpy sea conditions. I don't have flat. 1m swell + chop is about the smallest. Biggest problem is ventilation of the wings. Its super easy with cross chop and swell. So it becomes incredibly hard to go fast and not expose a wing.

TI threading capability!


you dont have a normal stock and die, and some cooling liquid ?

Getting Closer !!!!!!!!!!!!!!!!!!!

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dachopper said..

Getting Closer !!!!!!!!!!!!!!!!!!!

wow . . . CNC power . . . looks great.

DO you have a link where some info on this machine can be found?

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max_ob said..

dachopper said..

Getting Closer !!!!!!!!!!!!!!!!!!!

wow . . . CNC power . . . looks great.

DO you have a link where some info on this machine can be found?

Not really - I designed and build it myself,

I can tell you what some of the components are and a rough ballpark, but to get something " off the shelf " this big to do what we want, was going to be 5 - 10 grand US.

Build area is 200mmZ, 800mm X and 1400mm Y

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max_ob said..

dachopper said..

Getting Closer !!!!!!!!!!!!!!!!!!!

wow . . . CNC power . . . looks great.

DO you have a link where some info on this machine can be found?

openbuilds.com/builds/openbuilds-ox-cnc-machine.341/

Well . . . dachopper . . . you should tell us more . . .

cnc machined G10 wings for racing?

cnc machined molds for the mast and fuselage?

I can tell you more. It's Solid carbon fiber - the whole thing was machined. Titanium lugs :)

I've experimented with the masts as I was curious to see the difference of a machined block Vs a machine block wrapped with anti twist oriented fibers..

What I can say is that I believe - the machined block without anything on it appears to offer better or the same stiffness than adding additional layers after.... It's substantially stiffer than G10 too.