BUT what are the virtues of having thick fins VS thin fins. I am not really interested in the obvious flex properties but more the hydrodynamics of thicker foils VS thin ones.
They both have their followers and the elite are advocating the SOAR style moulded foam core which is quite thin and without any real feature other than weight.
Then there are the Bert Burgers who seem to like them very (very very) thick and I presume would also argue that they are of a higher performance…
But who is right? The FCS H2 is the fastest, free-est fin I have ever used and it’s quite thick (thicker than standard fins anyway), similarly Future must have something thicker than normal so I am open to either but is it the foil shape on a thicker fins leading edge that helps or just the foil section that is allowed more roundness per area.
While I’m sure there are surfers here who could explain the technical virtues of thicker fins better than me, I think they work much better. There’s more area to get a fuller foil which works smoother…
Do a search on the topic. This question got addressed at some length a few months back. But to summerize for you, thick is superior to thin. Properly done, the fin won’t stall in high AOA turns, and will carry almost as much speed out of a turn,as you went into the turn with. Blunt leading edge is a major contributer to that performance.
I’m not an expert but from my experience i can tell you that i prefer thicker fins in small waves because they give me more release and lift and i like better thinner fins on bigger waves because they’re faster.
I think in the archives there’s a lot of info about this, specialy from Halcyon, Tom D., Bert and Blakesta.
What’s true is that you have to be really good to be able to shape a good foil on a thinner fin.
the h2s are heading in the right direction , they are visably and measurably thicker with a way softer leading edge …
gumby!!
theres some old threads , (fin theory , tom halycon and others ) (thick fins vs thin fins ) and (fin theory , vector forces ) if you get through that lot in the next month , then you should get something out of it and get some questions answered …
regards
BERT
hey gumby , i surfed those chunkas today , man what a difference to control …
i could hook the tightest turns , even from posistions of relativly low speed , i put em in a long board and could get 12 o clock reos in waist high waves , the same board with the previous fins and i needed at least a head high wave to get 12 o clock , because i needed a longer approach to draw the turn , coz the fins didnt handle high AOA with out drifting or losing speed …
stoked that long time board builders with a life time of experience like thrailkill would state the facts so simply …
Do a search on the topic. This question got addressed at some length a few months back. But to summerize for you, thick is superior to thin. Properly done, the fin won’t stall in high AOA turns, and will carry almost as much speed out of a turn,as you went into the turn with. Blunt leading edge is a major contributer to that performance.
For each point there can be a counterpoint.
Thin fins generate lift more sensitively. At the small angles of attack operating in a thruster bottom turn, stalling is a non-issue, so using a thin fin lets you work closer to the high-lift end of range.
Thin fins are also lower drag at zero angle of attack. Always.
Surfboard fins from all major manufacturers have evolved to the thinnest fins possible without having an inordinate compromise from excessive flex. Shortboard thruster sets are 0.25 inches thick at the base, and longboard fins between 3/8" and 1/2". In hydrodynamic terms these are 5-6% thickness relative to chord length. A full foil would be 12% or so. Or twice as thick.
There is a good thread in which this is discussed at length. If stalling were relevant, increasing fin thickness may help. And, if you are running one of the older obsolete fixed fin systems in which you run fins at -3 degree AOA when you go straight, thicker fins will speed you up.
But in my rotating fin boxes, thicker fins generate less lift and have more drag. Its application specific.
In the later 70’s I had some riders living on Maui that surf the bay quite often. When they requested a new quiver, I built them boards with glass centered foam fins. I thought I was onto something of a break through with my thick/pronounced foil fins. Nothing was farther from reality, at speed the pronounced cord would set-up a dramatic low pressure behind the thick spot, resulting in the tail suddenly shifting the the right then left. I got a quick response from the boys that being slotted towards the bowl and having your board squirrel out was no picknick. Well that put the super thick fin theory to rest !!!
This is very interesting to me, Yes, thin fins will have less drag at a 0 angle of attack, but the angle of attack on a surfboard fin is almost never 0. angle of attack is not 0 when you are going down the line, as there is both the component of the flow parallel to your line of motion and a component of the flow perpendicular to it. Thrusters come closer, as the fin is not set parallel to the board’s direction of motion in an attempt to account for the flow of water up the surface of the wave, but I’d be willing to bet that there is still a significant angle between the fin orientation and the flow direction. I am not sure about in water, but in the wind tunnel, thin airfoils generally stall somewhere between 10-20 degrees, which isn’t all that much. On a thicker airfoil, flow separation occurs a little later, maybe enough to make a difference. Ha, this is starting to sound a lot like class. anyway, I can definately see the merits of a thicker fin for a singlefin, and the thin fins perhaps catch up a bit with regard to thrusters, I know this is in water, but some basics shouls carry over. Also since there is only one tip, that might make some difference. The best way to figure it out is definately to surf a bunch of different finsthough, but I don’t think there is any harm in trying to analyze it while I am stuck here unable to go surf, sure beats doing actual aero homework.
Jim is pointing out what should be obvious in all cases. Different conditions warrant different equipment.
Different conditions are the open ended equation. Size, shape, speed and power of wave; size, shape, experience, and power of surfer; and, of course, size, shape and design of surfboard and fins.
How many grains of sand are there? How long is a piece of string? How many stars in the sky?
Doesn’t really matter, as long as you know they’re all there and they’re all different. Finding the ones you like is what the fun is all about.
Does anyone here remember when it used to be FUN ???
Has it ever occured to you that people are discussing it because it is fun for them. The great thing about a forum like this is you only have to read what is fun for you. I only read about 1 in 4 posts because they are the ones that look fun to me (and comment on even less). The knowledge that I have been gaining here has made surfing more fun for me, not less fun.
BINGO, you hit it. For those who like the academic side of this, I rode a 3/4", and a 7/8" thick foiled fin, with a 10" base. On the emperical side, I rode guns with the described fins in medium to huge surf at the following beaches; Sunset, Pipline, Laniekea (15’ glassy), Waimea, Makaha. There was no lack of necessary speed to routinely make the waves, no twitching in the tail, just good solid hold with ease of turning. All single fins. I can see the potential for handleing issues with multi fins that are toed in. A serious mistake with thick foiled fins, in my opinion.
remember the delammed fin I posted a shot of a while ago ?
Well , that was a thick fin .
It went really well. I REALLY liked it !
Unfortunately , the delam let in water, and the fin …well… delammed, for want of a better word . Sad day.
I have now pulled off the delammed outer layers . I left the tabs thick [so they still fit the plugs nice and tightly].
I now have the same fin in nearly half as thick a version .
Once I have foiled it [harder to do , for me at least , as it is now pretty thin , and more ‘flexy’ than before] , I will hopefully be able to report back my findings .
I fully intend to make a thicker one again of the same template , so I can ride BOTH , so I’m not relying on my memory from a month ago , when comparing them .
Here’s a shot of the ‘delammed’ fin …before…
And, after, with the delam pulled off (not foiled yet , though …)
From your picture it looks like you've got a light layer of say 4 ounce cloth capping a coarse layer of woven roving. They will flex at different rates and have a tendency to "delam".
