Point breaks can allow for longer drawn out turns. But, they can also be great venues for quick hard snapping redirects. To answer your question though, A more vertical template clustered more closely together will allow for quicker tighter turns than a more raked template that is placed further apart.
Tom is correct…that’s one of the main reasons Slater is using his signature blue FCS fins…ideally suited for vertical surfing and tighter arcs.
Getting back on subject, I’ve been having some thoughts about cut-out fins, drag reduction, AOA, etc etc.
QUIZ…
Besides adding additional compoments/fins, what can be done to the board bottom shape near/around/in-front of the front fins to:
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reduce drag at the base of the fin
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maintain a more optimal angle of attack in rail to rail surfing
???
Im thinking along the line of small vees, concaves and large dimples…
Anyone try?
pimples
This is probably cheating, and I won’t do it again, but I just had to rescue this thread from the obscurity of page two by saying something about fins
Tunnel fins are really great and have a great and glorious future.
Roy
One might argue the rise of 2 fin boards over singles, and of three fins over two fins, was due to high speed projection down the line during bottom turns.
The projection is due, in large part, to the rail fin being angled relative to the stringer, or toe-in. Without this, there is no thrust in thruster.
Whereas I can see how hold and control may come from your tunnel fin, I cannot see how it could project one down the line through a bottom turn. Of course, these elements are most easily grasped on shortboards - I can thrust on a 6 foot board a lot, on a 7 foot board a little, and hardly at all on boards over 8 feet long.
So I have a coupla questions. Am I wrong about projection with tunnel fins? How do they compare to thruster setups on shortboards?
Hello Blakestah,
The toe in angle of the thruster can be described as an angle relative to the rail. An angle between the rail and the fin can also be achieved by having the rail line pulled in. Thus my pintail boards achieve a difference between rail line angle and the forward facing foil. A more parallel rail line with a tunnel reduces the projection somewhat but there is still plenty.
The projection factor for a tunnel is influenced more by the fore and aft trim of the wing. If one lifts the nose too much, projection is lost, but if the nose is kept down a bit, drive and projection is great. That's why I like a big heavy board for a tunnel board, but it needs to be light enough that you can still lift the nose when you need to. For a very light shortboard this fore and aft trim has to be constantly kept correct using muscular control.
I can be a bit complex to describe the behaviour of the tunnel fin because it acts in so many directions, so talking about it can give the impression that they are complex to ride.
In fact the tunnel fins are simplicity itself to ride if they are set up properly. It only takes a session or two to dial in to them.
Roy
Blakestah,
I too find that most boards over eight feet have zilch projection. This is because most boards over eight feet come from a place called ‘Malibu La La Land’ . Malibu La La land is a place where boards are designed to do piffy little tail turns and noserides. Projection is a lost cause for these boards because of their reverse rockers (tail lift and not much nose lift). My X-15 has amazing projection. By the way there are plans for these boards on my site.
Roy
Pimples was not a joke. I guess no one bothered to check my work. Or thought I was kidding. I get that alot. That’s the problem with new ideas and new technologies. No one knows what the heck you’re talking about.
For starters:
http://aerodyn.org/Miscellanea/tech-request.html
RoyStewart: Have you tried cutting a tunnel fin in half and placing the halves in a more traditional array? I bet it looks a lot like a Webber CRV. Or how about a less than circular tunnel fin? Something like an ellipse that might make better use of the Bernoulli Effect. The way foiled thrusters do. I think on a narrow tailed board like the one you pictured you may have a good thing going. But on a board with a wider tail for high performance turning perhaps not.
Also, the Nozzle Effect could produce some instability and backpressure. I think your search is for the optimum tunnel shape and size. Is this along your line of thinking and testing?
Hello Mark,
You are suggesting putting a half pipe on each rail. The trouble with that idea is that it would be almost impossible to put the board on the rail at speed. The tunnel will roll on its central axis without any resistance but it will not be shifted sideways (including up or down) at speed, which is why it has so much drive. You could of course change the shape of the tunnel into (for example) a flattened ellipse. The effect of doing that would be to increase rail to rail resistance. The fin would of course work that way, only not as well.
When I say that the tunnel can’t be shifted laterally, I should mention that it can turn perfectly well, but can’t be moved parallel to the way it is pointing.
The Bernouilli effect is not a very effective theoretical tool for analysing these foils. It is more useful to visualize them more as water direction units.
You mention that I might be searching for the ultimate shape for a tunnel fin. In fact I am not. The perfect shape is circular, and although I agree that the circular shape could be altered I can see no gain in doing so. In all the cases where the wing shape is altered there appears to be some disadvantage, even if it is slight.
To be honest, riding these things is really easy, and they are completely viceless if set up correctly. Setting them up correctly is really easy also.
Here's a picture of a wide tailed tunnel board. It's a kind of fun board.
All the best, I'd better try and find those pimples.
Roy.
https://swaylocks7stage.s3.us-east-2.amazonaws.com/s3fs-public/1000834_foilboardpics%20086#.jpg
https://swaylocks7stage.s3.us-east-2.amazonaws.com/s3fs-public/1000835_foilboardpics074#.jpg
hmmm/ pimples… might have something there… after all, raised bumps were used on golf balls near the turn of the century to add control and lift before they went to depression dimples. How would you test this? Perhaps a dropper bottle of resin and a lot of time on one’s hands? I can’t picture this adding anyting but drag, but hey, why not t
Quote:
ry it?
Mark, I found an entry for the effect of pimples on marine hull surfaces but couldn’t find the actual info. Roy.
Tubedog,
regarding your feedback with the cutaways…you said that the board lost some drive and gained tighter pivoting…I offered a couple of modifications (longer center fin base, canards, twinzer, etc). From your feedback, it appears that lost drive is an issue.
Then I started to think of the board shape around the front fins…
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why not use channels to gain back the lost drive?
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a small Vee in front of the fin to redirect flow away from the base in the turbulent zone near the board.
Mark,
Pimples…wasnt sure if you were kidding or not. So youre suggesting using them as trips/turbulators in front of the fins to reduce drag? On the fins?
Youre a microfin guy…I think I finally figured why small canards work and now I have some ideas on how to optimize location and toe. From my personal experience, sticking canards on a standard thruster setup loosens the board but you lose a little forward projection and drive…thus the whole fin setup must be modified…going with LokBox on my next board…
I had an epiphany the other day while thinking about this thread and I sketched a concept board which will feature the following:
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rear-half: center rocker more relaxed than rail rocker (concave under front foot, Vee in tail)
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LokBox fin mounts
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cutaway front fins (about 5/8" high)
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two (or four?) channels
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light/moderate Bonzer-esque concave
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small Vee ahead of each side fin
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optional mini canards
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turbulators/trips on fins
(I can always use regular fins if things dont work as expected)
Its a freakish design, but Im confident it will outrun any board Ive owned to date. Plus it will be fun to shape, experiment and optimize (I have to satisfy my gearhead addiction).
A big THANKS to everyone who has contributed to this thread!
If you go to design your own fins, I recommend looking at fins you like, and measuring the chord length at the base, 1 inch up, 2 inches up, 3 inches up, etc. And measure the rake angle.
Pivoty fins that don’t project probably lack chord length. If you shorten it at the base, you can lengthen it higher (in the next series).
Hey Roy,
The Bernoulli effect will be doing it’s thing no matter what. If you are certain that you want to stick with one shape perhaps you could alter the foil on your shape to benefit from the lift. No one says lift has to be up. Are you foiling your tunnel as if it were a wing rolled up with the foil on one side? If you did that maybe you have a foied shape that at one point pulls the tail down and that will be fighting the floatation and cause drag. Note: Kelly likes his boards to ride tail down so I’m not going to say it’s a bad thing. However if you were to change the foil on the bottom of the tunnel to generate upward lift and the sides to generate outward lift then you might utilize lift and get even more speed. Generally I’m suggesting you have options regarding tunnel shape and foil while still using a tunnel. The round tunnel does give you the most flow with the least amount of surface area but you can control the nozzel or venturi effect by changing the overall shape of the nozzel or tunnel. Perhaps looking at paint sprayer spray patterns or pressure washer spray patterns for more ideas on this. remember Edison said he found 6,000 ways not to make a light bulb. And people are still looking at ways to make them even better.
Cutoffs as they relate to Webber’s curved fins: I’ve read that he goes skating across the wave cutting back with ease, but I’ve never used them myself so I should not comment. I’ve also read that they are for very light people.
One thing is for certan you have completely altered the tip vortex. I’ll have to think about that more before I comment.
As for the pimples I havnt found any studies yet. I havnt really looked hard either. I was hoping someone else would do that:-) Or maybe no one has published any. That’s the way it is with new ideas.
Quote:
Hello Blakestah,The toe in angle of the thruster can be described as an angle relative to the rail. An angle between the rail and the fin can also be achieved by having the rail line pulled in. Thus my pintail boards achieve a difference between rail line angle and the forward facing foil. A more parallel rail line with a tunnel reduces the projection somewhat but there is still plenty. </blockquote></div>I find the stringer line is a more accurate way to describe the effects of toe-in. All fins are toed in relative to the stringer, not relative to the rail line. People that set fin toe-in angle relative to the rail, instead, soon find out the mistake they are making.
Quote:The projection factor for a tunnel is influenced more by the fore and aft trim of the wing. If one lifts the nose too much, projection is lost, but if the nose is kept down a bit, drive and projection is great.I find there to be a significant increase in turning efficiency when fins are angled relative to the stringer. Such boards rapidly came to dominate competitive surfing. When you turn an angled fin, water hits it and is deflected towards the rail and tail. The forces are roughly perpendicular to the fin surface. You get pushed forward, and you get pushed towards the rail (projection and hold).
If you play with the angles, even a little, you will see that a one degree change in toe-in angle on a thruster rail fin is enormously noticeable. A quarter inch toe-in works out to about 3 degrees of toe-in. If a shortboard is toed to the nose, it is about 5 degrees. Virtually all shortboard thrusters operate in this range. More toe is more projection and less hold - and vice-versa. The effects are very powerful.
I just don’t get how this process - the process of converting speed towards shore to speed down the line - or the basic bottom turn - is aided by the tunnel in a way it is not aided by a single fin. The tunnel and fin do not deflect water in an angle relative to the stringer, and as such, can generate, at best, very very weak projection. The projection has to come from reactive forces on the hull and rail instead - as it does on a single fin board.
Further, I am a little hesitant to try anything on such a long board. The hull length has a substantial impact on the boards ability to turn. I don’t ride boards longer than 6’6" until the surf is pretty big.
I know it can be difficult to understand a new concept without riding it, so it could be I am way off. But I like to think about how fins and boards turn, and I am having a hard time seeing how an efficient bottom turn would be aided by a tunnel.
VGs and turbulators.
Dimples and pimples.
What works better in water and why?
How do they both relate to turbulators?
What’s a pimple? I think the most interesting research lately has been on the fins of the Humpback whale. Have the link somewhere but my bookmarks have grown to encyclopediamaniacal proportions.
Questions without answers. Yet.
Anyway If I was going to be funny this is more along the lines of my level.
Hope it doesnt offend everyone. If so I’ll banish myself. I could use the free time.
Quote:
When you turn an angled fin, water hits it and is deflected towards the rail and tail. The forces are roughly perpendicular to the fin surface. You get pushed forward, and you get pushed towards the rail (projection and hold).
In addition, the direction of water flow (relative to a front fin) is radically different between the flow near the board’s bottom (turbulent layer) and the flow above it. I modified my clear/acrylic model test board yesterday and will test soon to prove this theory for myself.
oh, I don’t know. I can picture how a tunnel fin affects bottom turns pretty easily.
Just as a gross oversimplification, look at it this way… picture a standard fish-type board, i.e. twin fin, no toe in. Now picture nailing a flat chunk of fin stock across the tips of the twin fins, sort of like a lid on a box?
Now, go surf that board. The minute you turn it, that extra horizontal surface connecting the fins comes into play, like a foil board or an extra amount of surface area on the bottom of the board. (More complicated than that because of where it is, but at a minimum it’s more planing area.) That’s certainly going to affect the turn…
Now, a tunnel fin is similar to that, but a lot rounder. Regardless, it has some horizontal surface area added to the vertical surface area. (again, it’s more complicated, because it also has surface area at all the other angles in between, no matter which way you roll the board you’re putting some new portion of the fin in play.)
I think its a pretty interesting concept and might even make one of these for a board I’m glassing… maybe…
Mark,
I have used tunnels which are foiled on both sides and tunnels foiled on one side only. They both work well. Whether or not the tunnel lifts the tail up or pulls it down is most easily adjusted by the angle of the foil in relation to the bottom (it’s a bit like thruster toe in but in the vertical plane). If you make it so the wing lifts the tail slightly then you will go even faster. Setting them up to direct the water parallel to the bottom is a good place to start. If you foil the fin only on the outside the effect will be to direct the water slightly towards the bottom, so this can be compensated for by a bit of toe in in the vertical plane. Also I am sure that you can have fun making different shaped wings. I am rather conservative and prefer round ones.
Roy
Blakestah,
Water does not have to be deflected at an angle relative to the stringer for an effective bottom turn, that’s just one way of doing it. Please allow me to repeat that the tunnel finned boards have tremendous drive and projection. This is their main feature. The tunnel will not sideslip during a bottom turn so no energy is lost. Your suggestion that the tunnel setup is capable of only “very very weak projection” is way off the mark. Of course my boards draw different lines from the modern thruster. THe point is that they have amazing drive and projection.
Cheers, Roy.