Hey John - I wasn’t saying you shouldn’t, was just curious about your thinking! FYI, of all your reasons I liked these 2 the best:
*Why not?
**It’s a good way to make use of broken boards.
Keith
Looks like a cool concept. Any ideas what you are going to construct the prototype out of?
CoyoteSurf’s idea of an m shape seems valid to lessen wetted area, but the shape you have them in seems more of a bigger wave setup. Similar to the quads being ridden at Mavs, toed-in outer fins with two parallel center fins. Maybe think about bringing the hoop into a tighter radius so the trailing fin can benefit from the leading fins wake turbulence, ala twinzer.
I’m not familiar at all with paipo’s but that seems like a lot of fin surface area for that size board. What is a typical fin setup on a paipo and the surface area of that relative to your setup? Seems like it may make it kind of tracky. Try it and see.
Single or double foiled?
Another benefit would seem to be no tip eddies or vortex drag hopefully with less overall drag than a comparable conventional fin setup.
Didn’t someone draw a sketch similar to that a while back?
Any ideas what you are going to construct the prototype out of? - Yes. Fiberglass/foam/carbon fiber/epoxy composite. Same as I used on a single hoop design. It seemed pretty strong for it’s weight.
M Shape - Cool idea. I’m going to try and finish this design first.
Quad-like - Yes. Nothing new there though. Quads were around before I’d ever heard of Maverick’s and not necessarily in big waves. Guys ride Boogyboards in big waves with no fin at all.
Tighter radius/ala Twinzer - The directional flow idea behind this version isn’t really about the slot effect or feeding off turbulence.
Relative fin surface - I don’t know. I suppose it ranges from no fin to quads and various relative sizes. Larry Obrien has a twin fin paipo with some tiny fins. Terry Hendricks has some huge hydrofoil supports (foiled and fin-like) on his far out paipo.
Kind of tracky - With a paipo in general, you can grab it with both hands, lean and wrestle it into any direction you want. They’re short and from my experiences, generally quite maneuverable.
Single/double foil - It will have a transitional foil. Asymmetrically foiled at the outer bases (flat inside/convex outside) with a symmetrical foil at apex of hoops and on inner bases. Attempts will be made at shaping a leading edge at the apex that allows for change in angle of attack without stalling when utilizing rocker curve.
Similar Sketch - I might have missed it. If you find it, please post… I had a heck of a time trying to draw my version! The photos I posted are of my very first attempt at freehand cutting out of poster board so I could get a better visual. Later attempts lead me to believe that I got very lucky on the first try as far as shape and general design. I am working on trimming it down in overall size and dimension but the curve on the paper template arches into a hoop with the angles and overall shape I was looking for.
The hoop concept in general is actually pretty old - I’ve seen a photo of an early design by Richard Deese from '64. Mike Doyle experimented briefly with a hoop. Roger Wayland has been doing some interesting “Hydro Tube” versions on paipos… (http://vagabondsurf.com/WaylandHydroTubesTwo.html)
Roy Stewart down in New Zealand is putting hoops on his long wooden boards and paipos.
I haven’t seen any dual hoops with shape and foil I’m working on. Thanks for the input - please let me know if you come up with anything.
Here’s the picture I was referring to, posted by daddio:
Looks like the single loop turned out really nice!
How did the single loop fin ride?
Yes - Credit to Daddio on diagram - I missed that one!
The single hoop seemed to ride nice but I’m not a very experienced paipo or bodyboard rider. It felt more secure from behind the peak and I experienced none of the sideslip I’ve found happens sometimes on finless designs. Sequence below illustrates.
Photo sequence by Jeff Chamberlain…
How are these fins going? Whats the feed back ? Is it worth making them up in carbon to go on a hollow wood fish?
Hi Crabman -
R&D continues. I’ll leave it at that.
Those look great! A+ for thinking outside the box.
Historical note: I recall “Soapy” Warsh (cousin of a small-kid friend of mine) either rode a tunnel fin in “Ride the Wild Surf” or had one at the time. This would be in the middle 60s, forget when that film came out. I saw the board around that time, it seemed to be a standard-issue 60s log with a tunnel about six inches tall, slightly taller than wide. There may have been a small vertical “finlet” at the top center of the hoop but it would have been only 1/2 inch tall or less.
As I recall, the board I saw was in near-new condition. Soapy, the board and the concept disappeared without a trace, except for the free thinkers in my eighth grade shop class making crude plywood paipo boards in shop class.
My thought on this latest version is mostly… why? what is there possibly to gain, except to make something different to tweak the shorebirds? You gotta have more time on your hands than I do, to go through with this. I’m jealous!
Well it’s safe to say that the tunnel concept is alive and well over here, as you know perfectly well.
By the way John’s ‘hoop’ fins are not true tunnels as they don’t enclose the water flow (probably why they are called hoops).
Enclosing the water flow is VERY important, which is why John’s hoops can never approach the efficiency of a true tunnel.
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Historical note: I recall “Soapy” Warsh (cousin of a small-kid friend of mine) either rode a tunnel fin in “Ride the Wild Surf” or had one at the time. This would be in the middle 60s, forget when that film came out. I saw the board around that time, it seemed to be a standard-issue 60s log with a tunnel about six inches tall, slightly taller than wide. There may have been a small vertical “finlet” at the top center of the hoop but it would have been only 1/2 inch tall or less…
Edition 1 of Stoked-n-Board shows a picture of a fin that looks exactly like what you describe, down to the aspect ratio and the finlet. Calls it a “wishbone” fin. Photo quality could be better, but it appears to have some kind of diamond-shaped logo decal or embossing on the outside. Vintage is about right, too, as it dates that fin type in the 1960’s, with the specific example photographed from 1964…
Sorry John, didn’t mean to be an accessory after the fact to hijacking :->
-Samiam
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By the way John’s ‘hoop’ fins are not true tunnels as they don’t enclose the water flow (probably why they are called hoops)…
Can you elaborate on what you mean by “enclosing the water flow”, and why John’s prototype doesn’t qualify? If it is the angle and the twist, remember that typical water flow across the bottom of a board is closer to a 45 deg. angle to the center line than parallel to it. If your concept requires a certain volume, column length and/or pressure of water to be “enclosed”, I can see it.
-Samiam
Yes the enclosing the flow issue is about water pressure inside the tunnel , the extremely narrow tunnel is at a disadvantage in this respect, also if the water flow is coming in at 45 degrees to one tunnel it is striking the other one at around 90 degrees, a bad state of affairs which will negate any benefit gained from the first tunnel. When we add the flared aspect of the hoop, which further increases drag, with no benefit whatsoever, and the resistance ( and consequent drag ) caused during rail to rail movement by non centrally mounted tunnels, then it gets worse.
Really the tunnels works best as we are already using them. . . centrally mounted, inlet area equal (or nearly so ) to exit area, upright with no rake, and an aspect ratio of around 1:1 to 3:1
It’s really simple to get right, like this:
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Hi Roy -
Here is a pic of 1964 Richard Deese fin. Paul Gross received credit on Surfboard history website. I know it isn’t as fast or as efficient as one of yours and I don’t know if it qualifies as a “Tunnel” fin, a “Hoop” fin or whatever.
By definition (yours), to properly qualify as a “tunnel” does a fin have to conform to a certain formula whereby the length is a factor of the width or heighth?
When a board is surfed beyond flat plane, I.E. when the angle of attack changes as tail rocker is utilized in turning for example, does a long tunnel fin reach a point where the tunnel no longer allows water flow to wrap around the leading edge? At what point does the water flow break away from the laminar surface and create drag? At what point does the long tunnel create an internal laminar effect that causes tracking?
My name was on the top of your post. I’m not sure if you were talking to me, or just clicking on the last post name for a general reply.
I don’t think just because it may have been done before that he isn’t thinking outside the box. I’m not the slightest bit familiar with any of this stuff, but there is one or two possible big advantages in a setup like that that just jumps out at me. Does that mean that will be the end result, or even the desired result? I have no idea. But the journey sure is fun isn’t it?
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Hi Roy -
By definition (yours), to properly qualify as a “tunnel” does a fin have to conform to a certain formula whereby the length is a factor of the width or heighth?
No not really John, but it does have to enclose the water flow, and since your fin is called a hoop and doesn’t enclose the water flow, it seemed like a useful distinction
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When a board is surfed beyond flat plane, I.E. when the angle of attack changes as tail rocker is utilized in turning for example, does a long tunnel fin reach a point where the tunnel no longer allows water flow to wrap around the leading edge? At what point does the water flow break away from the laminar surface and create drag? At what point does the long tunnel create an internal laminar effect that causes tracking?
If they are made very long (low aspect ratio ) the angle of attack which they can handle gets lower, an aspect ratio of 1:1 to 3:1 is a good place to start
Talking about the angle of attack on the tunnel changing as rocker comes into play is not an issue because the tunnels are set up either parallel to the bottom or at a low angle of attack of 1 or 2 degrees at te most. . . thus the bottom of the board controls the angle of attack on the tunnel in the vertical plane, and they work together.
Rail to rail they are of course the loosest fin it is possible to make.
Regarding " An internal laminar effect" there is very little of it, that’s the whole point of enclosing the water flow. . . it evens out the pressure in the tunnel, thus almost eliminating pressure layers and the friction between pressure layers which results from them moving at different speeds . . . . the aim is to avoid differences in pressure.
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Nice work john,looks great…would love to ride it !
Hope all is great for you ! Herb
Hi Roy -
Thanks for the explanation. Apparently I was typing some of my questions as you were already answering some of them in the nearly simultaneous post. I hadn’t seen your post yet as I was typing mine.
I like the looks of the hoop in your paipo photo. That one looks like it would work fine.
To be honest, my dual hoop concept was misplaced in the shuffle. I was surprised to see this thread brought back from the dead. I do have a shaped paipo hull to which I hope to attach the dual spiral hoops. There seems to be less at stake with a paipo… you aren’t as inclined to lose your balance if something goes haywire. You can also drag a leg or whatever to regain control. My Hawaiian “guitar pick” paipo has no fins at all but by grabbing the forward rails and wrestling it around, it can be controlled.
In any case, an ideal design is a tough call with so many variables. I tried attaching a hoop fin using FCS plugs for experimenting but the hoop was ripped out in a high speed crunch on a sandbar. A new hoop has been fabricated and installed and I hope to get some feedback on the paipo ride with hoop and with standard keel twins. If it can be established that the hoop gives an advantage, I suppose fine tuning of the general design might be better accomplished.
As it is, I’m more or less winging it and it is basically for kicks. My first hoop fin paipo design was a blast. In nearly ideal waves, I really had fun with it. It is also fun just to see people’s reactions.
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……If they are made very long (low aspect ratio ) the angle of attack which they can handle gets lower, an aspect ratio of 1:1 to 3:1 is a good place to start ……
Low aspect ratio foils are more tolerant of angle-of-attack (i.e. they stall at a higher angle-of-attack than a high aspect ratio foil). However, the maximum lift coefficient generated by a high aspect ratio foil (all other factors being equal) just prior to stall will be a little greater than the maximum lift coefficient just prior to stall of the low aspect foil. In short, the lower aspect ratio foil will have a wider range of angles-of-attack between a zero lift condition and maximum lift than will the high aspect ratio foil (but the latter will have the greater maximum lift).
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……Regarding " An internal laminar effect" there is very little of it, that’s the whole point of enclosing the water flow. . . it evens out the pressure in the tunnel, thus almost eliminating pressure layers and the friction between pressure layers which results from them moving at different speeds . . . . the aim is to avoid differences in pressure. ……
I assume that by “pressure layers” you mean three-dimensional “layers” of water of essentially constant pressure. If that is the case, then it is erroneous (or at a minimum, highly misleading) to talk about “friction between pressure layers” since isopleths of pressure are not congruent with the streamlines of the flow. Note also that pressure differences acting on the foil are what generate “lift” (i.e. the component of the force on the foil that is normal to the free stream velocity) – hence avoiding pressure differences, means avoiding the generation of lift.
kinda on topic, kinda not.
pretty amazing nonetheless.
the guy in the red survival suit is pretty good.
the guy in the wetsuit, not so much.