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Wave oriented hydrofoil

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ahmthai
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Wave oriented hydrofoil

Postby ahmthai » Thu Jan 14, 2016 3:47 am

I made a 45cm hydrofoil designed for light wind and small wave riding. Following are the design criteria:

Limitations of most current designs:
-The long mast requires the wing to travel on a large arc through the turn. The wing will need to travel 2-3m on a cutback or bottom turn. If you look at most hydrofoil wave videos people are riding straight down the line or doing one turn on to the wave.
-A long mast requires deep water
-Speed oriented foils are often too fast and will outrun the wave (even when not being pulled by the kite)
-Most higher aspect foils require decent board speed and will dramatically stall at slow speed

Design criteria:
-Fast turning
-Shallow draft to allow riding through shallow water and over reefs
-Shorter mast will reduce the arc the wing needs to travel through on a turn.
-Low stall speed
-Compact front wing to limit the wing tip coming out of the water.

Short mast

-Reduce the arc the foil travels through a turn.
-Allows you to ride in shallow water and over reefs
-Accept that you will touch down often and may end up riding on the board at times

Front wing
-Compact, mid aspect design
-Thick profile for low takeoff and stall speed. A thick profile is also strong for impacts
-Front wing anhedral to limit the wing tip coming out of the water with maximum wingspan.

Rear wing
-Relatively small with no anhedral/diahedral for maximum turning. Anhedral/dihedral limits turning (increases tracking).

Fuse
-Thin for efficiency and smoothness through the water
-Strong to take impacts
-Not too long for increased maneuverability.
-I purchased “The Kite Foil” short stainless steel fuse.

Board
-Relatively wide with some volume for stability when touching down. Needs to be very strong to handle frequent touch downs.
-I modified and Airush Slayer 54cm V1.

Results:
The down side:
It took some time adjusting to the short ride height and limiting touchdowns. Unlike a long strut, you need to adjust to the swell, but this is what we do when riding a surfboard on the water, so not difficult. You need to accept frequent touchdowns, but because you are not coming from a great height, it is easy to ride through them. You can’t lean too far back or the front wing will come out of the water.

The upside:
Really direct connection with the foil which allows fast, confident turns. The board and foil feel like one. You can make the same aggressive turns you would with a surfboard. Carving down the line is much easier than a long foil and no worries about hitting the bottom. Unlike with any other setup, I can carve powered down the line in 8-10 knots in small waves and shallow water.

Jumping is MUCH easier than a long foil as there is no delay between loading and coming out of the water. Landing is also much more forgiving.

Learning: My wife is learning and she feels MUCH more confident on the short strut than the long one.

Overall I am very pleased with the results. You might consider it "hydrofoil assisted" surfing because you end up in and out of the water, but it is really fun to ride regardless.

What I would change:

-45cm is the limit to how short the strut should be. Adding 10-15cm would greatly reduce the number of touchdowns and (hopefully) not reduce the maneuverability and direct connection feeling.
-I replaced the initial rear wing with one about 30% larger which increases pitch stability, but did not affect turning speed much.
-I would make the front wing slightly larger with a thicker profile for a lower stall speed. The current wing is good, but it would be better if the stall speed was even slower to make low speed transitions smoother. The thicker profile will limit the top end, but that is not a concern for a surf oriented foil.

Cheers,
-Andrew
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Starsky
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Re: Wave oriented hydrofoil

Postby Starsky » Thu Jan 14, 2016 2:28 pm

That is awesome.

Your breaking ground. So many things to tweak. Stoked to see where we end up for pure wave riding.

Interested to see how your thoughts evolve regarding mast height. Going short for maneuverability is novel but it comes at the cost of accepting a certain amount of touch down, which in turn dictates a lot regarding board. Its an interesting concept. Lots of wave foiling will be in small waves/shallower water and at slower speeds. Might suit a certain amount of surface riding. The shallows will always be a trade off where foils are concerned!

The other end of the spectrum is to increase maneuverability by eliminating swing weight ( in addition to reducing fuse length and vertical aspects of the tail as you mention ). Going from a 6 foot surfboard to a 40" skim makes a huge difference in maneuverability but it almost requires a certain mast length in effort to eliminate touch downs.

The future is bright. Keep tweaking.

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Re: Wave oriented hydrofoil

Postby Peter_Frank » Thu Jan 14, 2016 6:00 pm

Great, good thread :thumb:

I think there are many ways to obtain this, as I've gone a different path - but ever since I learned, have always chased waves as my main goal and liking :naughty:

Riding small waves in say 10 knots with a 9m2 is fantastic - eventhough you often slice through, or have to because of chop and small distance between, but you can still whip the cutback on the face of a small wave/crest, or at least try to as you (sorry, "I") relatively often fail if going for it.

I have chosen by experience, some quite different preferences -

For small waves, a LONG mast.
Have had both 80 and 90cm, but chosen a 100cm now.

When I went from 80, and had ordered a much more expensive 100cm (race) mast, I was really thinking: Damn if it will make turns wider and feel less "awesome" when carving, as in theory it should turn wider.

But I found to my surprise that I could not feel any disadvantage whatsoever - in fact I could often carve tighter on the longer mast, because of more clearance so you could push harder without the risk of ventilation or the board catching :rollgrin:

For "travelling" in waves, the short mast is really bad (IMO, at least for me).
You have to get used to ride lower, yes, like Andrew also points out - but this is not a problem when experienced on several masts, you get used to changing your "default" ride height..
But ventilation happens sooo easy with a short mast, or you will hit the crest of the waves with your board - so the longer the better, no doubt at all when talking about riding in chop waves (straight).
Also more clearance (safety margin) on the waveface, so ventilation wont happen, as ventilation will always lead to disaster :cry:

The depth is of course the risk, as small waves occur (and only curl) at reefs or sand banks.
I mostly ride at sand bank spots, so the trick is to be so confident that you never touch down when carving DTL, and IF you are about to or make a mistake, you jump off your board (thus strapless almost a must).

This means, if (when) you crash, you have to boarddrag a bit out, in order to start again :wink:
But you can ride and do turns on small waves where it is relatively shallow, when you just stay "up" - quite fun and a good challenge so you get even better :naughty:

If I touch down, even if ever so slightly just touching the top of the wave with my board - I almost feel like I've failed totally and feel lousy :roll:

So riding sometimes with the board on the surface is NOT an option IMO, and seems more like some misfit between hydrofoiling and waveboard waveriding.
Others would call it an awesome compromise - so different likings I know, and find it great that it works !
Personally I ride both hydrofoil and waveboards in waves, and prefer not to mix them up, just like the mutants have died many years ago, as better having either a full on TT or full on waveboard..

So my short mast is used in marginal onshore winds now, as here you can not get out to start because the kite will drop if trying to drag out - not possible.
So a short mast and you can get up from where you can go out keeping the kite in the air in 8's just overhead, and then start without hitting the bottom - to get out to deeper water.
And in marginal winds, our water is always flat - so a short mast is great then :cool2:


As said, the opposite choice, but our goal is the same just different paths, to have fun in the small waves in low water :naughty:


At first I liked a big lifting wing, as one could just put the pace down.
This still goes fine often.
But it seems, the more experience you get, the faster wing you find works even in small waves - and if a bit bigger waves, faster wings that also TURNS faster is awesome :naughty:
A lifting wing is good though, but I would much rather use a faster turning wing, even if a bit smaller thus requiring a bit more speed.

So a wing with a low span is my preference, turns much faster and I find in contrast to your findings, that they turn way faster and easier, and no "bubbles" in hard carves.
I dont like too low AR wings though, so it will have to be smaller in area because of that (just me, I know)
But in low winds, around or less than 10 knots I agree, a bigger wing is better and the choice.


Swing weight - like Starsky says, really important.
Prefer using a light board, smallish, and round edges so you only have to fear the foil when you crash in a wave.


Agree, not too long fuselage is good, as you will often hit the bottom when starting in low water "tail low", after a crash in the small waves - and maybe it turns faster.

I am maybe just babbling on - but I love having fun in waves, and cool to see different approaches :lol:

8) PF

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Re: Wave oriented hydrofoil

Postby revhed » Thu Jan 14, 2016 6:33 pm

:thumb:
May I ask what profiles you are using for STRUT, F wing, R wing?
Any chance of a board photo with rails as well?
Strapless?
As I fly the Med sea, not waves very often but when there are sure fun, and as said lower AR 4ish thicker F wing seems to work better than my thin 6ish.
I have a feeling that if I lived near a wave spot that a 70 cm strut would be fun to have.
R H

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Re: Wave oriented hydrofoil

Postby plummet » Thu Jan 14, 2016 9:55 pm

Real interesting man. This maybe what i am looking for. As i am in a location of waves, waves and more waves.

Plus rock, boulders and more rocks. A wave orientated foil with lower mast may work well for my location with less chance of smashing into the boulders that lurk suprisingly close even hundreds of meters out to sea!.

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Re: Wave oriented hydrofoil

Postby tegirinenashi » Thu Jan 14, 2016 10:30 pm

The best insurance against damaging hydrofoil when hitting underwater object is fuselage design. For example, one can easily imagine bulbous nose with rubber cover, so that when hitting something, you don't immediately destroy wing or fuselage (or both). I'm still waiting for an explanation why submarines, tankers, and other water vessels use bulbous noses, but kite hydrofoils insist on sharp (and dangerous) fuselage spike.

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Re: Wave oriented hydrofoil

Postby Peter_Frank » Thu Jan 14, 2016 11:29 pm

tegirinenashi wrote:The best insurance against damaging hydrofoil when hitting underwater object is fuselage design. For example, one can easily imagine bulbous nose with rubber cover, so that when hitting something, you don't immediately destroy wing or fuselage (or both). I'm still waiting for an explanation why submarines, tankers, and other water vessels use bulbous noses, but kite hydrofoils insist on sharp (and dangerous) fuselage spike.
I have had both spear sharp spiked fuselage noses, and also blunt ones (like just the leading edge itself)

I will say there is no signivicant difference in the impact with a sand reef, as the spike enters slow and nicely till a full stop, and the wide nose or full LE enters even more abrupt.

But of course the latter is safer regarding getting hit in the neck when crashing :-?

8) Peter

Spike:

Image


Blunt or non-existent:

Image

8) PF

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Re: Wave oriented hydrofoil

Postby Sir V » Thu Jan 14, 2016 11:51 pm

Hi guys, I ride a custom 750 mm strut. I got it made specially for waves, I am still trying different wing profiles..

This was taken last year in October and I am now progressing a lot faster ;). My goal is definitely waves, not interested in flat water or racing, each to his own..

https://www.youtube.com/watch?v=WNYBSvACIf4

Cheers, V

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Re: Wave oriented hydrofoil

Postby Peter_Frank » Thu Jan 14, 2016 11:58 pm

Sir V wrote:Hi guys, I ride a custom 750 mm strut. I got it made specially for waves, I am still trying different wing profiles..

This was taken last year in October and I am now progressing a lot faster ;). My goal is definitely waves, not interested in flat water or racing, each to his own..

https://www.youtube.com/watch?v=WNYBSvACIf4

Cheers, V
Yes, but that is not "small wave" riding, which is really different ?

8) Peter

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Re: Wave oriented hydrofoil

Postby plummet » Fri Jan 15, 2016 12:10 am

Peter_Frank wrote:
Sir V wrote:Hi guys, I ride a custom 750 mm strut. I got it made specially for waves, I am still trying different wing profiles..

This was taken last year in October and I am now progressing a lot faster ;). My goal is definitely waves, not interested in flat water or racing, each to his own..

https://www.youtube.com/watch?v=WNYBSvACIf4

Cheers, V
Yes, but that is not "small wave" riding, which is really different ?

8) Peter

They look like sweet waves. But they don't look big either... maybe shoulder to head high? But its hard to tell with gopro footage.

A shoulder high wave in my book is small...


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