Fin theory,tom,halycon and others

General Discussion
201

sabs,

 I understand that you're looking for a simple method for experimenting with camber while maintaining plane form. By relying upon a thin plane form and adding microballoon filled resin to move the camber around or increase/ decrease it, I think you'll end up with some thing that will have irregular flex properties. And, unless you reinforce it with a schedule of laimnate it will want to crack. So, why not take either an existing fin template from a fin system and modify that fin. That way you start out with the same plane form and just remove material to change camber. If you want to add camber you could start with a bigger template and work it down. Another approach would be to layup a thick sheet of fiberglass and cut out a series of the same plane form templates and then sand in your various cambers.
202

Halycon, what about putting a bit of rake on that upright fin, or does that defeat the whole purpose of the experiment with vertical rake in the first place? Here’s a photoshopped pic with 20º of rake added. By adding rake to the same plan shape you are in effect adding a little length to the chord. Just a thought.

203

Mike,

So what you’re saying in simple terms is that you have to rake the leading edge to get any power out of the fin.

Oh, Tom’s right if you want to experiment with fin foil and thickness. Starting thick and taking material away is the best way to do things. He’s also right about the flexiblity changing as you thin the fin down. The best way to minimize this problem is to use G-10 which is expensive, heavy and very hard to foil. Anyone option is to make panels will lots of layers of carbon fiber in them and lay them up with a high grade epoxy. This well help the end product keep a greater measure of rigidity as you thin it down experimenting with different foils.

Off to work, Rich

204

halycon!!! i dont rate those upright fins either ,they lack any real drive out of turns and if you work your board it wont go any faster , the most bizaar thing tho? if you just stand on your board and theres that little bit more push, they go like a rocket…

one thing they do well is turn amazingly tight , but then you stop…

unless your falling back into the pit…

the ones of mine in the pic are huge , i made three sets, they kept getting bigger and bigger ,there never gonna be a small wave option…like you i placed them in the realm of high speed foils as far as the template is concerned…they have way less drag…

my theory on that one was ,trailing vortex …

when you have a raked fin , because you have a pressure difference on both sides(like all assymetrical foils) water form the high pressure side wants to get to the low pressure side, the raked template allows water to wrap the leading edge but in the process it starts a spiral ,that spiral of water continues to be fed all the way along the leading edge to the tip ,so at the tip theres now a vortex that is being dragged along by the fin …

where as a vertical leading edge doesnt allow that vortex to get a start , coz the water cant wrap around the leading edge from the high pressure to the low pressure side …so you wont get as much drag from the trailing vortex phenomenom…

i think sabs is thinking along the lines of my question before ,

i wanted to know if everyone agreed with my statment that if you move the thickest part of your foil(camber) forward or back , you basically move the low pressure region forward or back with it…

i shouldnt of put a photo of those vertical fins in ,it probably threw everyone off the point i was asking…

also still related …if you have a region of low pressure on one side ,then surely the most force against the high pressure side is directly opposite where the least pressure is on the low pressure side…and that by moving camber around we can move our low/high pressure region on our foils…

coz ive made some interesting observations from moving the camber around without changing the templates…

but i feel the changes i felt are due mainly to what i spoke about above …moving the low pressure region around…

so what im asking for is confirmation on that theory …as it is the key to unlocking the other observations ive made and giving them some sort of logical explanation…

i wont go into any other subjects till were all thinking about the same subject…

then i think we can look closer at this area …

got a new toy today … gonna post a pic its not a fin …just a surf pic…

regards

BERT

205

http://www.vacantisw.com/foildesign.htm

the basics…

you’ll see why moving the camber fore and aft will change lift characteristics…assuming all else constant…its a trade-off between the ability to maintain lift at large and variable angles of attack versus drag.

Although this thread has been very enlightening Im really torn by it. What’s better for the rider…improved lift/ability to deal with large AOA’s OR reduced drag…very hard to achieve both simultaneously. Im on the reduce drag side of the fence…lift/speed can easily be gained by using wider/flatter boards. Add the fact that few (or none of us) really knows what kind of angles the fins are dealing with…very elusive thing, angle(s) of attack on a fin.

A lot has been said about speed and I still believe it is dependent on the wave, the board and the surfer’s ability to generate speed (Im on shortys). Unlimited speed is NOT a good thing…I can easily outrun a wave to the soft shoulder but I’d rather stay in the pocket…that’s where speed is an undisputed good…having gobs of speed out of a roundhouse cutback in the process of getting back to the juicy pocket. Projection out of a turn is where I believe the holy grail of speed lies…but how? Better lift or reduced drag? Is lift even a factor during a big round turn?

Would everyone agree that singles are best when turn radii are large and also projecting out of big turns? In the singlefin case its about low drag and much less about lift (lift from a single fin?). So again Im on the reduce drag side of the fence…

So now…how do I get singlefin-esque projection out of three finner while simultaneously maintaining its excellent tight pocket turning ability? That’s my goal and hopefully some of you agree too.

BTW Bert…I was watching longboardTV on my dish the other day and there was a guy riding one of your boards at Raglan…perhaps that was U? I think it was a contest. Not only a gearhead but also a minor surfTV celebrity! I would’ve never noticed until you started posting pics of your unique wood boards.

Halcyon,

Could u get the guts you needed if an additional set of smaller fins where installed in that config? Like a twinzer but perhaps faster down-da-line?

206

meecrafty, my goal was getting single fin drag and three-finesque projection. But there is more to it than that.

BTW, you can fairly accurately measure the angle of attack with a rotating single fin. You simply increase the size of the maximum angle of rotation, and use little side force, and then ride it. At too large of an angle the board will start to draw a tight spiral spin-out with no drive - the fin angle approximated the angle of attack, and you lose it.

Greg Loehr stated he thought (and I tend to agree) that shortboard and fin design was driven to give the rider the best action off the bottom turn. The critical thing is to change from going straight with the wave, to projecting down the line as fast as possible. Optimizing this performance element has resulted in the most competitive success so far.

Also, Bert, vertical fins generate a vortex just fine. They need to be low aspect ratio, though. The leading edge vortex depends on the aspect ratio being low enough. The biggest drawback to the vertical fin is their limited angle of attack. They hit maximum lift:drag at too low an angle for hot-dogging on surfboards at lower speeds. If you make a vertical fin with a low aspect ratio, it will generate gobs of drive at low angles of attack. If the aspect ratio is too small, it will feel gutless. The starfin is a low rake, wide, low aspect ratio, fin (aspect ratio close to 2).

It’s been my contention that leading edge rake was set appropriately for matching the angles of attack. If you observe carefully, you will see that

  1. longboard fins are 5-10 degrees more upright than shortboard fins

  2. almost all shortboard fins by all manufacturershave the same leading edge rake

  3. windsurfing fins, which deal with more limited AOAs, are more upright than longboard fins

  4. wakeboard fins, and kiteboard fins, are even more raked than surfboard fins.

  5. the Takayama fins from Red-X are specially designed to go with longboards as rail fins - they are more upright than the shortboard fins

Further, if you make a rake series, and keep chord lengths the same, and fin depth, and just adjust rake, it becomes clear that more rake leads to higher drive at small AOAs, but more limitation in viable angles of attack. In choosing a planshape, the leading edge rake is one of the most important variables. I’'m not suggesting using vertical fins - but take your favorite fin and tilt it 5 degrees on way or the other. The difference in the ride is very easy to notice. That was mainly the point for me in using a straight leading edge - it made studying rake easy to do.

It’s also kind of interesting that surfing planshapes generate the most lift closest to the board, although some think planshapes like the Halcyon Mental, which moves the lift away from the board a little, are better. This is a function of chord lengths close to the base, and close to the tip. One of the things I don’t like about flex fins is their tendency to generate lift closer to the fin tip - thus generating a heeling torque.

Also, Bert, with respect to foils that generate low pressure through a leading edge vortex, lift from the low pressure side is highly concentrated close to the vortex - close to the leading edge. The low pressure would be closer to the wide point of camber is the fin were high aspect ratio and lacked a vortex.

I would be interested to hear about techniques for optimizing foiling. If you make a camber cut-out, it will be specific to one chord length, and difficult to replicate accurately enough from base to tip. If anyone has any tricks, I’m all ears. I generally start with a plate, use a sharpie to draw the wide point, and foil the leading edge rounded, and the trailing edge pointier, but my technique is quite crude.

207

Hello Meecrafty,

Since unlimited speed has not yet been experienced by any of us then how can we say it’s not a good thing? Some people used to say (just after the steam train was invented) that if you went over 60 mph you would die of asphyxiation. Of course this turned out to be false. There is something in what you say about outrunning the wave, though. As a speed freak I find I am constantly outrunning the wave at regular breaks that other riders find quite fast or challenging. The trick is to find faster waves. Closeouts are really good because no matter how fast you go you never outrun them and you will always end your ride in the pocket

Roy

208

Hello Chaps, I am following your discussion about upright fins and fin rake etc. with interest and have here a picture of a longboard fin, this one is attached to my seventeen foot redwood pintail and it has loads of power. It is fourteen inches deep and 22mm thick. Upright fins are great. Roy

https://swaylocks7stage.s3.us-east-2.amazonaws.com/s3fs-public/1000807_Star%20board%20pics%20021#.jpg

209

Here are just one person’s results with tinkering with the theories recently posted on this excellent thread. First, I am not a fin foiler, so my results may be affected by that. I’m just tinkering. But I would classify myself as someone who is very equipment sensitive, unlike many of my friends who could change fins and never report feeling any difference. The following experiences were on the same 6’2 standard thruster on fast shoulder-high waves at the same reef over several days. My first experiment was a duplicate of Meecrafty’s FCS G5 cutaway trailing base. I noticed an increase in pivot ability off the top but a decrease in projection off the bottom. Next I double foiled the leading edges to maybe 90-10. I noticed another slight increase in ease of pivot, but again a slight loss of ability to set and angle and push hard on the fins to gain extra projection and perhaps a slight loss of straightaway speed. Next I took a pair of Rainbow fiberglass FCS tab fins and double foiled the leading edge to maybe 90-10. Again I felt a slight loss of speed and loss of ability to set a turn angle and hit and hold the turn hard. Next I trialed a set of the new concave/double foiled FCS FG-5 fins. They are probably a lot better foiled than my efforts, and appear just a bit thicker than usual FCS fins and so can handle a better more rounded foil. Anyways they rode very lively in small waves, with noticable better planning lift and lightness in the tail perhaps due to the fact they are foam and more bouyant like other fins I’ve had like that (ie AerCore glass-ons). Perhaps the slightest loss of straight-ahead speed over regular fins but made up for it when worked down the line in turns. I’ll keep experimenting, but for now I seem to like the foam concaves in small waves but would prefer the more familiar foils perhaps with slight cutaways in faster waves where the waves provide all the speed needed. Also theoretically this may reveal board design implications- on larger wider boards where planning provides all the glide and speed you need, perhaps the cutaways and double foils would help with turning. But on thin small performance thrusters where speed needs to be generated and maintained by thrust turns, perhaps traditionally foiled wider based fins allow for speed generation by means of resistance, through propulsion from hard carving turns with force. One thing- I recommend you don’t hit the fiberglass/foam FCS fins on reef - they nick quite easily. Comments?

210

You cannot just remove material and expect an improvement, necessarily. If you want a true-er test, make a set of fins of the same fin area as your current thruster fins. Copy the leading edge. Remove the trailing base material and add it slightly higher - make them Mental.

Basically, this shifts the fin forces slightly higher on the fin. It is in a much better position to optimize lift:drag, and should be more powerful than the standard fins.

The cutaway you did may have improved the lift:drag ratio, but if it also made the fin area too small, it wouldn’t work for you.

211

Bravo Tubedog! A man of true action.

Youre feedback is the best Ive read in a while.

I’d be on it too but unfortunately its totally flat in the flaccid penis state.

Personally I would not sacrifice bottom turn hold and projection.

I find it interesting you noticed a difference when double foiling the leading edge…you are sensitive!

Agree with Blakestah on maintaining area. If you want to tinker some more get the twin fin size front fins and use a smaller cutaway…maybe only 5/8" high cut out…for smaller boards, I don’t think the turbulent layer under the board is very thick at all, particularly planning high…like Bert opines, about as thick as the sheet of spray off the board…

other thoughts…

say you use cutaways…move the front fins back a little and add a small canard (much smaller than Rusty’s) to lengthen the effective base (???) and hopefully maintain drive/hold. I have used small canards and they dramatically change the feel of the board…felt like the front fins were set too forward…very loose.

What if you supplemented the lost front fin area with more center fin area?

this is the direction my noggen is going today…

Blakestah, what kind of sheet do u use to make protos? PVC?

Roy, wave pocket speed is limited and that’s whereabouts the speed I like to go.

The fastest surfing is being done at Jaws via toe-in and Laird (the king of Jaws) rides a reasonably standard three fin set-up…wave, surfer, board…

212

McMaster-Carr, 3/8" fiberglass sheet (made with polyester resin), I get 4-5 7.5" fins per sheet, the material is the same as regular fins, but lower in quality. About $22, you can get it in 24 hours. It is plenty stiff, fine for prototype work, but a lot uglier than the stuff normally used.

If you want to try a “Bert” thickness fin, you will need 3/4" sheet.

I use it principally b/c I don’t have the necessary glass lying around to make my own sheets. But, if you make your own, it will be a LOT nicer material. However, it is pretty easy, I have good access to a bench belt sander, and can now foil a fin in less than 30 minutes, not bad for an amateur.

Now if we could only do something about the poor surf conditions…

213

Tomatdaum,halcyon

The thin sheet I make is a carbon layup with epoxy

Get a piece of formica ply the same size as three fins thats about 600 cm x 110cm

screw down each edge length ways a piece of 5mm formica

Now lay up cabon be it unis or twill etc dry untill you reach a level with the edges

Now one by one wet and lay each piece on when you get to the top screw down another flat sheet over it

The excess resin will flow out the ends ,oh and any raw timber edges should have packing tape on them

When it cures crack it out

You now have a piece of flat sheet If as I said in the last post you taper it from the middle down to the edges, you will now have a fin core

it will be slightly heavy but will have 0 flex ,its a good starting point later when you get plan shapes and foil cambers that you like start to intrduce lightness and flex

The balloons will not crack and you can add or take away as you please It good for fine tuning

Halcyon

All I way saying was that if you persue more upright fins then as Blakestah says the aspect ratio has to stay lower

You need tip area.a point does nothing

Blakestahs plan template posted awhile ago has tip area that will provide a pressure difference and therefore lift

A spit fire wing is a hell of a lot bigger than a fin,some things dont scale down that well

Just to add some fun to this I will post some pics of the sloted duel fins soon

these are two foils working together to act as one foil

Cheers Mike

214

I’m reading this thread from the beginning and it’s really interesting, and since my english isn’t good enough, i’m printing all the thread (more than 160 pages + photos) to read it at home with a dictionary close to me. Of course, i’m learning a lot with you guys, so thanks to all of you who share your knowledge with us, especially Halcyon, Tom, Blakestah, Bert, etc.

I just wanted to make a comment on the “unlimited speed” thing, and is that i believe that having a surfboard and a set of fins that give us “unlimited speed” would be really good.

If you have unlimited speed, being in the pocket is the surfer’s work. I mean, you don’t have to use your speed just going on a straight line, is your work riding the wave trying to get all the power it gives you. Sure you’ve seen Slater on any video, and the difference between Slater and the rest is that he’s always lots of speed, even at the end of a hard turn.

I think that’s where Rich’s fins are going, his fins make your board feel smoother on rail to rail changes, and allows you to carve easier while maintaining the speed and holding better than any fin i’ve tested.

I have fins that hold a lot, yes!, but they’re anything but fun, because trying to do a good turn with this set up, is a nightmare. Then i have fins that feel very loose, but they have two problems: they don’t hold enough and/or they do “square turns” more than carving, and square turns make you loose a lot of speed. “Pivoting” is good when you’re surfing a noserider with 1’ waves, but isn’t fun on 5’ hollow waves.

So if sharing your knowledge you find a set up of fins, that gives you “unlimited speed” (at least, a little more speed) and allows you to carve as hard as you want while maintaining all your speed: you’ll start a revolution in our sport, and it would be nice because we’re seeing the same things since the late 80’s.

One more think: when i read your feedbacks it seems like you’re talking always about the performance of the fins on long,clean point waves, and i think that most of the surfers in the world use to surf 1’ to 6’ beach break close outs… Did you tested your fins on those conditions? It feels really different when you’re going on a wave that has a different shape every second.

Thanks again to all the contributors from Swaylocks.

Good waves!

215

A 1 to 6 foot closeout is not very demanding of a fin system.

The feedback you get from linking 2-3 turns together, and from going rail to rail, and making multiple trips up and down the wave face, is much more valuable than anything you can determine in a beach break closeout.

216

Blakestah,

          When i wrote "1-6' beach break close outs", i meant a shorter wave with a shape that isn't always the same.  So i wanted to wrote that not everyone has Rincon, Malibu, Blacks, or Mundaka on his backyard. Let's change "1'-6' beach break close outs" for "1'-6' waves with a sandbar bottom". 



          Hossegor is a beach break, and so is Doninos, and you can get good feedback from there, but i'll be diffrent to one from a perfect point break. 



          Good waves!
217

Mate, the point is that if you have your act together you can link three or four turns and zoom up and down on a closeout. Sometimes also, one man’s closeout is another man’s long ride. chiz chiz Roy.

218

Right I think you are, Roy! One guy’s closeout is another’s off-the-lip re-entry/redirection or floater opportunity.

219

Actually, the best barrel riding practice that I ever got in was chasing the exit at El Portro. Going to Hawaii after several months of El Porto, made working the reefs much easier.

220

I was just talking about beach break waves, often enough to do 3 or 4 maneuvers, the shorter waves. OK this aren’t close outs, so my apologies because i didn’t use the proper word.

Anyone who surfed here in Galicia knows that we don’t have world class waves here, but we have a lot of good empty waves, mostly beach breaks with really consistent swells. Our waves aren’t bad, but they are different from Rincon or Malibu.

A perfect point wave often allows (or demands) longer radius turns and once you surfed some waves on this session you know how the wave is going to break on each section. While on a beach break you need to be more spontaneous, and it demands quicker/tighter turns, and you really need to be able to generate speed really fast if the wave’s face change suddenly.

I think now you’ll understand what i was talking about.

Good waves!