You guys know those hydrofoil boards that laird and his posse uses? the one with the air plane looking thing attached to the board? what would happen if you put a small one in the middle of a concaved nose (nose riding)? would that push it up to make it stay longer, and as you were turning would it catch on the water and throw the board the other way?
I have done that about four years ago.
I built a board with two wing hydrofoil fns, one at the tail, and one about one quarter of the way up the board. This worked well, the board cruised free of the water and had good control . . up to a point. It didn’t work too well in the tube, and the turns it pulled were like gentle banking turns. The best part about it was the smoothness, like flying, and the power of the foils could be felt underfoot, it was as if there were big fish under there towing the board (it is a little difficult to describe)
The next prototypes involved moving the front foil further forward, and using larger false bottom wings placed near the nose. These things were less successful and I abandoned them in favour of the tunnel fin.
I have seen a hydrofoil kneeboard on the rodndtube paipo forum which has (I think) an adjustable front foil attached to the nose and a fixed one at the back. Apparently this works (my front foils were fixed).
Tail based foils are well known for their ability to hold the tail down (and thus the nose up) when the rider is on the nose, but they impart a braking action to the board in this situation. A nose foil will not necessarily slow the board while lifting the nose but it wll drastically inhibit fore and aft trim ( if it is a fixed foil) and turning ability.
Flat wing foils will always inhibit rail to rail movement. This is a necessary feature of the boards Laird is riding, as the board is completely free of the water and needs some resistance to roll. For a surfboard which is intended to be used in the conventional manner, that is using the bottom and rails for stability and rail to rail resistance, the extra resistance to rail to rail movement caused by a horizontal wing is less desirable.
When designing hydrofoil boards it is important to remember that the lift generated by the foil increases enormously with speed. A tiny area can become very powerful at high speed, while being quite weak at low speed. Thus a hydrofoil board is prone to drastic behavioural changes as it accelerates if there are multiple surfaces set at different angles, or if the foil surface is not parallel to the bottom of the board. If the foil surface is not parallel to the bottom of the board then the bottom and the foil will fight each other. At low speeds the bottom will win the argument and the foil will create drag. As speed increases, the foil will become dominant and the bottom will start to lift. The transition between these two states requires careful surfing. These days I set foils up to be parallel to the bottom or with a very small angle of lift.
PS I have been building hydrofoil boards since 1997. I sent blueprints of my designs to Sam George in 1998 and received no reply. Three months later I saw Laird out there on his foil board. At the time I felt ripped off but I realise now that inventions often pop up simultaneously in different parts of the world. I believe that there is a kind of collective subconscious thought pool, and that if you think about something intensely enough that it increases the chances of someone else tuning into your thoughts and thinking of it at the same time.
See Roy?
I knew there was a reason I like you!
Around these parts, Rich Miller is making and using hydrofoil boards for windsurfing. Twin foils, varying sizes and configs, currently horizontal front wings at 20 degrees pointing down, flat tail wings.
He’s been riding them since around 1995, when most sailors thought he was the mad scientist…he does wear wirerim glasses, has long hair, is super Berkeley educated, and has all the characteristics of a mad scientist. He also tends to rub his hands together while talking about his new ideas.
Thanks Lee,
I am Auckland educated but I do also tend to rub my hands together when talking about new ideas, no glasses yet though! Actually we were living in the bush on Great Barrier Island during 1995 and making balsa singles 7’ to 7’5" when we were visited by a slightly crazed individual who said that he had been fed an LSD sandwich and then tortured by Ahipara locals who thought that he was after their crop. He also said that he had a secret fin design and that he was being followed by surf industry agents who were after it. He refused to even say what his fin design did but we fed him and he later bailed for the mainland. A few weeks later we came across a non surfing island character by the name of ‘Wetsuit’ who said that he been to the Okiwi bar ( an isolated but epic bar break on the Island) with the fin maker and that the guy had been flying above the water while surfing and that it was amazing to watch. Now this ‘wetsuit’ chap also believed that Henry Ford had built an entire car completely out of Hemp . . like every single part including the windows . . so I didn’t take too much notice but it stuck in my mind.
I wonder how tunnels would go on a windsurfer?
Regards, Roy
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I have done that about four years ago.
I built a board with two wing hydrofoil fns, one at the tail, and one about one quarter of the way up the board. This worked well, the board cruised free of the water and had good control . . up to a point. It didn’t work too well in the tube, and the turns it pulled were like gentle banking turns. The best part about it was the smoothness, like flying, and the power of the foils could be felt underfoot, it was as if there were big fish under there towing the board (it is a little difficult to describe)
The next prototypes involved moving the front foil further forward, and using larger false bottom wings placed near the nose. These things were less successful and I abandoned them in favour of the tunnel fin.
I have seen a hydrofoil kneeboard on the rodndtube paipo forum which has (I think) an adjustable front foil attached to the nose and a fixed one at the back. Apparently this works (my front foils were fixed).
Tail based foils are well known for their ability to hold the tail down (and thus the nose up) when the rider is on the nose, but they impart a braking action to the board in this situation. A nose foil will not necessarily slow the board while lifting the nose but it wll drastically inhibit fore and aft trim ( if it is a fixed foil) and turning ability.
Flat wing foils will always inhibit rail to rail movement. This is a necessary feature of the boards Laird is riding, as the board is completely free of the water and needs some resistance to roll. For a surfboard which is intended to be used in the conventional manner, that is using the bottom and rails for stability and rail to rail resistance, the extra resistance to rail to rail movement caused by a horizontal wing is less desirable.
When designing hydrofoil boards it is important to remember that the lift generated by the foil increases enormously with speed. A tiny area can become very powerful at high speed, while being quite weak at low speed. Thus a hydrofoil board is prone to drastic behavioural changes as it accelerates if there are multiple surfaces set at different angles, or if the foil surface is not parallel to the bottom of the board. If the foil surface is not parallel to the bottom of the board then the bottom and the foil will fight each other. At low speeds the bottom will win the argument and the foil will create drag. As speed increases, the foil will become dominant and the bottom will start to lift. The transition between these two states requires careful surfing. These days I set foils up to be parallel to the bottom or with a very small angle of lift.
PS I have been building hydrofoil boards since 1997. I sent blueprints of my designs to Sam George in 1998 and received no reply. Three months later I saw Laird out there on his foil board. At the time I felt ripped off but I realise now that inventions often pop up simultaneously in different parts of the world. I believe that there is a kind of collective subconscious thought pool, and that if you think about something intensely enough that it increases the chances of someone else tuning into your thoughts and thinking of it at the same time.
I am the designer/builder of the board at:
http://www.rodndtube.com/paipo/hydrofoil/paipo_hydrofoil.shtml
…and I’d just like to say it rides totally different than the characteristics Roy describes for his board. It’s design was optimized for maximum maneuverability, and everyone (a very small number) who has ridden it has been impressed with that quality. A recent rider’s comment: “With this board you don’t turn, you just think ‘turn’”. Speed is difficult to judge. Calculations suggest a 10-20 percent improvement over a state-of-the art board with a planing hull (depending on the skill of the rider), but uncertainties in the details of the velocity field in the face of the wave make the accuracy of those calculations uncertain. However, spectators have commented on it’s acceleration and speed–and sections do seem to disappear quickly. I have just gotten a GPS set-up (as described by “soul” in the thread “Speed Surfing Challenge”), so hopefully I’ll be able to make a more definitive and accurate statement as soon as we get some suitable surf.
The transition from displacement mode to flight mode occurs transparently (you don’t even notice when it happens) and at a relatively low speed (~ 5 mph) and the only significant change with speed is that–as with a bicycle–it becomes less “wobbly” (at very low speeds) as speed increases. You have to balance the board in roll–as with a bicycle; on Laird’s boards you have to balance it in both roll and pitch–as with a unicycle. The latter presents a much bigger challenge and work load for the rider–especially when aggressively maneuvering.
For the record, the first hydrofoil wave-riding board of which I’m aware was a plywood design by Gaylord Miller. I first became aware of this board when I arrived at Scripps Institution of Oceanography in the fall of 1960 (it’s also documented in the SIO publication: “Scripps Stories - Days to Remember”). A number of copies were made and ridden at that time (I know of at least one still in existence) and I made a copy in late 1960 as my first “real” surfboard. However learning to both surf and to ride that board at the same time was a bit too big of a step for me so I learned on a conventional longboard and (later) gave the hydrofoil board to Stan Pleskunas and Steve Lis.
The board pictured at Rod’s site is the seventh in a series of prototypes constructed (beginning in the mid-1990’s), and the second to last in a series of about 15 (or more, depending on how one counts) in a series of computer-assisted designs (including–for one of the earlier, and very unstable, designs–a simulator to train the rider).
As Roy says, the forward foil is adjustable–but not underway. It was made so that it could be adjusted in case the initial guesstimate of the rigging angle was not correct. As it turned out, the initial guess turned out to be the most satisfactory compromise between speed, maneuverability, and security against pearling. A more recent design has a number of improvements over the one illustrated at Rod’s site.
What I have found to be the greatest weakness of this design is that it makes a great kelp harvester–especially during a bottom turn. Second biggest problem is finding people who will actually try it (many talk the talk; very few so far have walked the walk). Independent assessments would be nice–I’m afraid that my impressions may be biased 
MTB
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You guys know those hydrofoil boards that laird and his posse uses? the one with the air plane looking thing attached to the board? what would happen if you put a small one in the middle of a concaved nose (nose riding)? would that push it up to make it stay longer, and as you were turning would it catch on the water and throw the board the other way?
The concept of a hydrofoil at the nose of a surfboard to provide lift (although not in combination with a concave) was an element in a patent (PSPTO #3,747,138) granted to Daniel Morgan (HI) in July, 1973.
I’ve been following this with considerable interest for some time now, and while I’m probably just repeating your thinking on the subject -
Would a little foil leading edge sweep help with the seaweed problem? Center of lift change problems could be minimised with a forward edge swept back, after edge swept forward foil such as used on the F-104 or X-15. Would make the calculations that much more difficult though. Might make for more gradual transitions/turns.
fascinating subject - and alas I’m late for work already…
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…,Would a little foil leading edge sweep help with the seaweed problem?..…
Some friends of mine who are developing a human-powered hydrofoil watercraft have experimented a little with this and found that the sweep angle needs to be pretty steep. That sweep substantially reduces the (induced) lift/drag ratio for the foil (although not nearly as much as a piece of kelp!) and introduces control problems (especially when aggressively maneuvering). But the vertical strut(s) connecting the foil to the hull is also a kelp collector and it’s not as clear how to configure the combination of the foil and strut such that one or the other doesn’t collect kelp. For example, even if the strut is swept as well, a piece of kelp could wrap around the swept strut and the slide down (and aft) along the strut until it reaches the horizontal foil–but then it can’t slip past that. Plus a swept strut in combination with a swept foil introduces some serious structural problems (and interferes with some refinements not present in the present board, but which will be incorporated into the next version). MTB
Hello MTB,
With a very large foil area, as in your hydrofoil boards, the lifting effect will be much more powerful and the transition between hull surfing and foil riding will be, as you say, much faster and will occur at a much lower speed. I have deliberately tried to keep the foil area as small as possible, and the lifting range of the foil as small as possble, to make the boards controllable by a stand up rider with no straps. The higher a board lifts, the more control becomes a problem.
I realised early on in the design process that I could go two ways . .I could either go for a full lifting foil and raise the board completely out of the water . . . or I could use the power of a horizontal control surface in a more subtle way, producing a horizontal foil based fin system which could be surfed by a stand up surfer in the normal way. I chose the second option, and thus discarded nose fins and massive lifting foils.
Hence the tunnel fin.
Regards, Roy.
PS I am looking forward to seeing a speed posted on the speed thread!
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I realised early on in the design process that I could go two ways . .I could either go for a full lifting foil and raise the board completely out of the water . . . or I could use the power of a horizontal control surface in a more subtle way, producing a horizontal foil based fin system which could be surfed by a stand up surfer in the normal way. I chose the second option, and thus discarded nose fins and massive lifting foils.
Hence the tunnel fin.
Did you accomplish a wooden board that doesnt need to be overtly walked
for leverage to turn??
i.e. trimming is not a total walking affair as it should be for a board of such
a length and weight because the tunnel fin is pulling the nose up all the time and doing half the job of keeping the board in trim??
…and since you 'squat’or are more reserved instead of doing drawn out bottom turns using your fully extended body with torque(shortboarding)
you probably dont need traditional ‘canted’ fins??
So the biggest problem to overcome was probably all that nose weight
which the tunnel fin makes humanly manageable??
Halsose, Thankyou for your reply.
In answer to your questions,
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There was no ‘problem’ to overcome. all the board designs which I use a tunnel on also work very well with just a single fin. The tunnel is designed to have a neutral effect on handling
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The wooden boards I build are designed to be surfed with less necessity for walking than is usual. They are not designed for noseriding.
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Your reference to the tunnel ‘pulling the nose up’ is overly simplistic. the only time that the tunnel holds the nose up is when the rider stands on the nose. Since my boards are not ridden from the nose this never happens. I was referring to the use of horizontal control surfaces as a noseriding aid which is occasionally done. I don’t use horizontal foils that way, but the thread started with a query regarding nose foils for noseriding.
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Regarding my supposed tendency to squat, I must say that I do drawn out bottom turns also, and that the tunnel works well in those situations. Canted fins are not necessary.
I realise that it is difficult to visualise the behaviour of horizontal foils without having practical experience of them in a surfing situation, so if you find what I am saying to be confusing, please let me know and I will do you a drawing or two to clarify matters.
Roy
PS ‘Traditional’ canted fins? You have a great sense of humour! . . . .Canted fins, a tradition hallowed by nearly thirty years . .man , you had me in fits, I laughed until I stopped, and more!
Right (writing late and tired and not entirely up to snuff ) - series of tradeoffs. Especially when aggressively maneuvering, that much less lift at the foil ends would slow down the turns. A reverse or forward sweep ( a’ la X-29?? ) plus a sharp center, like a minesweeping paravane, would deal with the kelp ok plus have a forward shifted center of lift when banked if the foil length and height ( having a mental block, correct terms are chord and…??? ) were constant throughout, but that introduces other problems.
That forward foil is pretty much straight horizontal, not a surface piercing ‘vee’ form ? Thinking about it, a vee form would be lovely for flat water but would …ah, ok, right… with one side of the vee in water and one side not, it’d get ugly and assymmetrical. Sorry, wasn’t thinking that through. .
drat - love to try it but it’s about 3000 miles from my local break.
doc…
The hull length places effective limits on available turning radii.
Toed in fins weren’t really appreciated until hull lengths got below 8 feet. Many riders of longer boards don’t think the benefits of toed and canted side fins outweigh the drawbacks. Few riders of surfboards under 7 feet feel this way.
It is my contention that longer hulled boards simply don’t have the turning capability necessary to take advantage of toed in fins the way that short hulled boards do. Until surf gets over 10 feet I rarely ride boards longer than 7 feet.
I’m pretty sure full hydrofoils are a tractable idea, but that it would require elevation-feedback to control AOA, and at least two foils.
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PS 'Traditional' canted fins? You have a great sense of humour! . . . .Canted fins, a tradition hallowed by nearly thirty years . .man , you had me in fits, I laughed until I stopped, and more!
…
You make a pretty good case there, Blakestah,
But why are you introducing the idea of toe in on a thread about hydrofoils, which are all about horizontal surfaces? To a horizontal surface, a positive angle of lift in relation to the bottom is the equivalent of toe in, but toe in is being discussed by you here in terms of regular side fin toe in, which is really just starting another thruster or twinfin conversation.
A horizontal tail based fin with a positive angle of lift in relation to the bottom is able to be 'pumped' up and down in much the same way as a regular board with toed in fins is surfed rail to rail.
Regarding double foiled hydrofoil boards, I have built standup boards with two horizontal wing fins which fully hydrofoiled and did not have a method of adjusting angle of attack. They worked, I actually rode them, like it's not just theory.
About turning: The turning capability of a board is related to the amount of bottom curve and planshape curve it has, not just how long it is. I have built several 12 foot pintails with 7 inches of rocker, and they were incredibly loose, in fact so loose that one shortboarder who tried one said that it was looser than his six foot thruster.
It is my contention that longer boards which lack turning ability do so because shapers have not yet cottoned on to the fact that to make a longer board loose you have to dose up the rocker and widen the board to get more planshape curve. As far as longer boards go the market offers only noseriders with relatively parallel planshapes and low rocker, or narrow, relatively flat ‘gun’ boards. These characteristics make a board which is hard to turn.
I can honestly say that my seventeen footer turns more readily than any ten foot plus foam ‘malibu’ that I have tried. This is probably not the right thread for length bashing either, but I must defend the truth where and when the opportunity arises.
Roy
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……I’m pretty sure full hydrofoils are a tractable idea, but that it would require elevation-feedback to control AOA, and at least two foils.
Yup. The SuperSlicer (now HYPO board) has two foils and an altitude-holding autopilot (at ~6" mean elevation above the sea surface).
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……That forward foil is pretty much straight horizontal, not a surface piercing ‘vee’ form ? Thinking about it, a vee form would be lovely for flat water but would …ah, ok, right… with one side of the vee in water and one side not, it’d get ugly and assymmetrical. Sorry, wasn’t thinking that through……
Yes you did!
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Quote:……I’m pretty sure full hydrofoils are a tractable idea, but that it would require elevation-feedback to control AOA, and at least two foils.
Yup. The SuperSlicer (now HYPO board) has two foils and an altitude-holding autopilot (at ~6" mean elevation above the sea surface).
MTB - is that your board??? If so, send me an email, I’d love to chat about other stuff.