The Squidtail

General Discussion
21

Well, I will buy that you’re re-directing water flow, for all the hydromechanical advantage you get by redirecting a relatively small area’s worth of flow that is the same V as the ambient flow a few degrees here or there. I note that you are shaping vertical foils now, so that’s interesting.

I’m not that invested in proving anything, but:

The upside down aircraft’s wing you mention is deriving Bernoulli lift from the (upside down) high AOA, given the curve of the (normally bottomside, here top) leading edge of the wing and the (normally topside, here bottom) foil–note the underside with high AOA effect of leading side of foil, and effective flat of trailing foil–highly inefficient trim though;

which toys are you referring to? I’m assuming by “fly” you don’t mean glide/slowed fall? By “highly efficient,” you mean a much smaller annular wing surface area/materials than one would need in a horizontal airfoil given a certain payload? Or a higher top speed in powered flight, better fuel efficiency, or higher terminal V in glide given a normal wing of identical surface area?

(Don’t get cranky about all this, 'kay? Just some Sways fun)

22

Hi Roy, all I was saying is that if the foiled side is the lifting side ( like on a wing) but you have it foiled on the outside, doesnt it mean that it would pull the tail down? Im gonna have to make one of these things I reckon.

Regards, spuuut.

23
Quote:

Hi Roy, all I was saying is that if the foiled side is the lifting side ( like on a wing) but you have it foiled on the outside, doesnt it mean that it would pull the tail down?

Quote:

No, it all depends upon the angle at which the tunnel is set up

Im gonna have to make one of these things I reckon.

Regards, spuuut.

They are easy to make, and I suggest that you foil yours both sides, they work very well that way, and if it makes more sense to you that way then that helps. Double foiled tunnels are easier to set up because in terms of lift angle what you see is what you get. . . flat foiled on the inside involves a bit of trial and error to get the effective lift angle sussed out.

I do have a spare 6" tunnel or two lying around (flat foiled on the inside) if you like I will send you one, on the house.

Are you longboarding at all ?

Regards,

Roy

24

Hi Janklow

Thanks for your thoughts

Overall your post is a tad frustrating from my point of view partly because you have no practical experience with tunnels, if you had then you would be singing a different tune. . . the overall trend of your arguments seems to be that the tunnel is just along for the ride and doesn’t do much. . . nothing could be further from the truth. . . the difference on the same board with and without a tunnel is enormous. . . . the increase in power and drive is dramatic. . . … . once you have felt it you can see it in the videos but unless you have felt you probably don’t know what to look for.

Here are a few points in response to yours:

(1) Bernoulli vs Coanda

Not much point in arguing this one IMO. Both theories are just theories, they have no independent reality and their usefulness depends entirely on their ability to explain what is happening. If you find that the Bernoulli theory is ideal for your understanding of lift then that’s fine, it doesn’t necessarily contradict my use of the Coanda theory. From my point of view, particularly in relation to annular wing based lift, the Bernoulli vs Coanda argument reminds me of the Ptolemaic vs Copernican explanations of planetary movement. . . . both theories are capable of explaining the movement of the planets but the Ptolemaic theory is unwieldy and complicated. Likewise I find Bernoulli’s theory to be lacking in that it doesn’t explain annular wing based lift (at least conceptually) very well. . … . annular wings create lift by redirecting large volumes of air or water with very little pressure difference. . . there is very little in the way of pressure layers inside the tunnel. . . this reduces drag and increases lift particularly at lower angles of attack. . . . . because the Bernoulli theory is based on pressure differences it is thus not useful at explaining how lift which is generated using minimal pressure differences occurs. . . whereas the Coanda theory explains this very well. Perhaps it is analagous to how light is sometimes treated as a wave and sometimes as a particle ? Thus I am not saying that one theory is right and the other wrong, just that one theory is more useful in one area and perhaps the other in another area. . . they are only mental constructs after all !

(2) Lift at low angles of attack

If I read you correctly you are saying that a lifting foil set up at a low angle of attack in relation to the bottom isn’t going to do much. Firstly I must suggest that you try it and find out. . . your feet will tell you the difference. . . this difference can be knee buckling ! Secondly, this noticeable effect is probably partly due to the fact that the enclosed tunnel is able to generate lift at lower angles of attack than flat plane wings (all else being equal). Thirdly, the tunnel has almost as strong an effect (from the riders point of view) when set up parallel to the bottom at a zero angle of lift in relation to the bottom. It is important, I think, to remember that even though the tunnel is parallel to the bottom it still experiences positive angles of attack in relation to the water flow. . . and the fact that the bottom of the board experiences something similar doesnt stop the tunnel from lifting when it meets water flow at a positive angle of attack.

(3) Low Drag

Annular wings are low drag, so the lift they generate always comes with a beneficial lift/drag ratio.

(4) Volume of flow

Annular wings redirect large volumes of flow compared with open wings of the same area ( I mention this because you mistakenly had the opposite idea)

(5) Lift in all planes

Unlike a flat plane wing the tunnel is capable of lifting through 180 degrees. . . so talking about its lift capabilities only in relation to the horizontal plane of the surfboard bottom is misssing much of the functional beauty of the tunnel. . . it lifts in any direction it is asked to. . . it does the job of a flat plane vertical fin and a horizontal wing. . . and all the increments of cant in between ! The bottom line for me is that I can’t stop riding them, they are so docile and obedient, and yet so powerful. . . neutral but positive

Don’t you just love these paradoxes ? :wink:

Sometimes when discussing tunnels I feel that a new less rigid language is needed. . . something of a tall order so will have to make do with the old english sentences !

I hope that helps us to continue a meaningful conversation

Regards,

Roy

25

Pardon my crude observation here, but those fins look like heavy duty PVC water pipe that have been cut in half and foiled…? We used to use them for irrigation, really tough stuff. If so, this is a brilliant use for it…

How do these fins hold up surfing whitewater?

26

Hi Simon,

A lot of our tunnels have been made from ‘plumbers pipe’ it does the job very well. . . the ones in the picture are glass and resin, made from a mould taken from a pvc plumbing pipe fin !

Regarding whitewater, the tunnels are really excellent because they gently redirect large volumes, thus ideal for chaotic low density water/air mixtures. . . . it doesn’t need clean flow because it makes clean flow !

Having said that, I should mention that this is provided that the surfboard is moving forwards. . . . there needs to be flow through the tunnel, whereas a flat plane fin will still provide lateral resistance when it isn’t moving forwards

.

27

I do have a spare 6" tunnel or two lying around (flat foiled on the inside) if you like I will send you one, on the house. Thanks Roy,I apppreciate your generosity, but let me muck around with my feeble attempts before I come to you for help ! And I will, I’m sure !!

Regards, Brett.

28

Say no more wink wink nudge nudge etc, mum’s the word !

:slight_smile:

29

Hey Roy, nice work, I would like you to meet my mate Fly, he has lived in Bali since 73’, been making wooden boards, has got great collection of stuff, if I said shit then , like I nearly did, it would have meant a difference to you Roy, and myself , also. I love Fly and I hope you get on that shapers list, what is that anyway? H.

30

Fair enough, Roy. Sounds good, or like something I’d try. I’ve been wrong before and I reserve the right to be wrong again and this time. I suppose I felt the need to have it all explained to me again in as concentrated a form as I could stimulate from you.

I was trying to think of a board I would use something with a possibly-knee-buckling lifting element. I do think it would be interesting to try something like a 6’10"-7’6"-ish, w/ the WP forward. Something with a fin box, to mount a traditional fin, a Starfin, and then epoxy a tunnel on. Kind of want something like that anyway. Maybe I’ll make one, and see if you have any left at that time. Would a fin box interfere so much it would contaminate my result?

How come you didn’t just use a full-round section in a smaller diameter, and/or shorter length? Or did you try that? You say you mount them how, in terms of AOA?

31

Roy, not that you would want to build it yourself…but do you think that your theories about redirecting a column of water could be applied to creating ‘tail hold’ for noseriding 20 lb low-rockered foam & glass boards?

Foiling the outside, directing flow upwards to push the tail down (or hold it in)…any comments?

It would sure beat hell out of glassing a brick onto the tail (which has already been done).

32

Hi HarisJ,

I’m sure I saw an article on Fly in one of the mags (Australian Surfing World?) about 10 or so years ago, making wooden singles, living in an amazing balinese house, I think he had a skin cancer problem and was out of the water ? How’s he doing these days ?

.

33
Quote:

I was trying to think of a board I would use something with a possibly-knee-buckling lifting element. I do think it would be interesting to try something like a 6’10"-7’6"-ish, w/ the WP forward. Something with a fin box, to mount a traditional fin, a Starfin, and then epoxy a tunnel on. Kind of want something like that anyway. Maybe I’ll make one, and see if you have any left at that time. Would a fin box interfere so much it would contaminate my result?

How come you didn’t just use a full-round section in a smaller diameter, and/or shorter length? Or did you try that? You say you mount them how, in terms of AOA?

No shortage of tunnels around here Janklow so just sing out when you want one, don’t worry about the published price.

Finbox should be fine, just remember to put the tunnel behind the single :wink:

A full round section mounted on a fin is the ‘tunnel on a stick’ model ( like the turbo tunnel) might be ok with a very small tunnel but with any significant area they are almost unrideable due to the axis of rotation of the tunnel being misaligned with the afore and aft axis of rotation (roll) of the board.

AOA wise, assuming a double foiled tunnel (easier to set up)the starting point is to run them parallel to the bottom, then for more excitement just add one or two degrees of lift, which means that the trailing edge is lifted 2mm higher than the leading edge (on a tunnel with a base length of 100mm )

Also a small 4 inch diameter tunnel is ok, we are using 6 and 8 inch diameter tunnels but 4 inch is a handy size.

.

34
Quote:

Roy, not that you would want to build it yourself…but do you think that your theories about redirecting a column of water could be applied to creating ‘tail hold’ for noseriding 20 lb low-rockered foam & glass boards?

Foiling the outside, directing flow upwards to push the tail down (or hold it in)…any comments?

It would sure beat hell out of glassing a brick onto the tail (which has already been done).

Sure, a tunnel will hold the tail in when on the nose ( I use this as a sign that I am standing too far forwards !) , no need to direct the water flow upwards, set it up parallel and then you get the best of both worlds, back pedal to the tail and you have a booster,

What happens is as soon as the tail tries to lift the tunnel the tunnel resists. . . same thing happens if you try to sink the tail. . . the tunnel always tries tio tunnel forwards in the direction it is aiming at, and resists lateral movement up down or sideways. . . it lifts by tunneling forwards on an incline not by

levitating laterally. . . … does that make sense ?

.

35

Sure, makes a lot of sense. Almost like a drogue - at least in terms of directional stability - but without the slow-down factor.

Your take on the half tunnel also makes way more sense to me than does the Turbo Tunnel - I’ve always doubted whether 99% of the surfboards sporting that particular apparatus had the right rocker to match it’s intended flow direction. Since your half-tunnels are mounted directly onto the rocker of the tail, they’d match up perfectly (at least to the extent you wanted them to).

Ever put them on squaretails?

36

Roy

Thought actually about a smaller diam. tunnel or a smaller chord same diam. on a 1" stalk or less, so as not to put it too far off the axes of the hull’s roll, yaw, pitch, time, space, etc (even affixing a full annular tunnel to the stump of a fin that would fit in a fin box…

IN the same breath, I thought about reducing chord say only along top, or making the side quadrants diagonal area to a reduced chord on top…

(I wasn’t thinking to gonna mount the tunnel at the same time as the single fin)

37

Benny,

Squaretails should be fine, I think any tail shape will be fine actually.

Cool that you are thinking about it !

:slight_smile:

38
Quote:

Roy

Thought actually about a smaller diam. tunnel or a smaller chord same diam. on a 1" stalk or less, so as not to put it too far off the axes of the hull’s roll, yaw, pitch, time, space, etc (even affixing a full annular tunnel to the stump of a fin that would fit in a fin box…

IN the same breath, I thought about reducing chord say only along top, or making the side quadrants diagonal area to a reduced chord on top…

(I wasn’t thinking to gonna mount the tunnel at the same time as the single fin)

Hi Janklow,

If you are thinking about just a tunnel ny itself you are in for some fun, I did a ten inch diameter tunnel, just the tunnel, and it was a blast, very sippery and loose but it did sideslip at low speeds (rather fun in little waves) , the squid tail is an attempt to do the whole business tunnel style but they work beautifully in conjunction with a vertical fin or fins. Strongly suggest trying one with the single in front, then take the single away !

You can muck around with the profile of the fin but keep in mind that it needs to be fully enclosed for some distance in order to keep the pressure even inside the tunnel, so raking it extremely or taking too much out of the top isn’t ideal

Tunnel on a stick is like putting the axle off centre on the wheel, ok for Fred Flintstone.

Thing is after having a crack at it then you don’t have to take my word for it, you know directly.

:slight_smile:

39
Quote:

Cool that you are thinking about it !

:slight_smile:

Don’t hold your breath :slight_smile: Not that it won’t happen…just waaaaaaaay more ideas than time right now.

Actually putting some serious thought into Janklow’s suggestion of some kind of partial tunnel bonded to some kind of finbox insert…I could probably get that done :slight_smile:

Roy - don’t be discouraged by this response! I have always put more value on doing than assuming. This one will get some time, for certain…

Thanks

Ben

40

Cool Benny, nice to see you guys ‘improving’ the already perfect fin . . you can’t do better than that ! :wink:

Just testing some homebrewed honey mead this one is orange honey and mace (no added sugar), about 13% alcohol, very nice

:slight_smile:

Anyway there’s a free 6" glass and resin tunnel in the mail for you if you say yes to it, got to have some kind of reward for thinking the unthinkable, and that way I can twist your arm away from the (hic) tunnel on a stick model. The 6 inch tunnel can just be glued on with a few drops of resin, it’s super simple to install. . . certainly easier than making a tunnel on a stick finbox thingy, and i know you have the perfect old log in there somewhere !

.