How THIN is too thin ?

General Discussion
1

i know it’s all about foil and displacement but thin fins give a similar control for a much simlpler price.

 I read an interview here with George Gall who said that the majority of a fins performance is due to its template ANd I totally agree as I’ve been using  3 mm Aluminium fins on my paipos , bodyboards, shortboards and longboards for,over 10 years.

A lot  of the fin hype is just that., if they can convince you to part with $200  because Kelly said so , then it’s more profit for them but what exactly are you getting for your fin dollars ??

is your new celebrity fin set worth the money, or is it just a purchase of pleasure ? Just a momentary buy because  the guy won a title this year ?

sure it’s OK if you’ve got money to spare, but why not look into fin design and decide if  theres any real benefit to spending a few hundred or not .

 Is that new fin really $200 worth of difference compared to the other 50 fins you have ?

 

2

George is one of the brightest minds building surf craft. I agree with his asssessment on templates and yours on buying for pleasure.  Templates are most important and stiff is good.

all the best 

3

I’ve seen photo of famous fin experimenter George Greenough with sparks flying as he ground down a stainless steel plate.  Allegedly he was after a thinner foil but it was a design for his sailboard.  Some of his kneeboard fins have a pronounced thick area in the foil along the base.  And then there is the ‘Paddle’ fin…  with the ‘mast’ relatively thinned out to allow twist.   

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4

Stainless steel…  

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5

I’ve been testing MrMik’s turbucled G.Whale 3d printed fins in various thicknesses in a very high mileage  board I have been riding for 15+ years.  Same exact outline, just different thicknesses and flex.

 

12, 11, 10mm, the 10mm was the clear winner in overall performance but the 11 and 12 were more forgiving and smoother through turns but did not have the top end, or the accelleration.  The difference between 10 and 11mm is still a bit of a mindscrew as it was obvious just paddling, and up and riding the accelleration and higher top speed was undeniable, especially after I broke the 10mm  cried, then tried the 11mm the next day in similar conditions…

 

I broke all of these fins, and MrMik reengineered the designs with better internal support.

 

Yesterday I tried a 8.25mm  thick fin, and found it too flexible on my heelside turns.  When it reached its limits and rebounded the whole tail of the board would sway and the rail would be unset.  A lighter weight surfer ( I weigh 215lbs) or one less dependent on loading the fin, would likely have had no issues and might benefit from the flex.

Today I rode a 9.9mm thick fin that is significantly stiffer than the 8.25mm fin and it is as good or better than the 10mm fin, which was the benchmark performance fin.

 

I’ve Also been measuring deflection putting 5 and 10Lbs of pressure near the tip of the fin.  The 9.9mm thick fin is almost as stiff as the 11mm fin of a different construction method which was the third best fin.  The better fins for me,  have all been the stiffer fins with one exception that employed a unique hybrid construction method and seemed to flex more near the base and was stiffer through the body.

 

I bet if the 8.25mm fin could be made as stiff as the 9.9mm fin, it would be the new benchmark.  The 8.5mm fin did not feel too thin, only too flexible when pushed hard, and when it was not pushed hard, it was a rocket, but occassionally would wobble and drag

 

Somewhere between Oz and LAX, a 9.625mm thick fin is on its way to me and i am giddy with excitement as I had an absolute blast today on the 9.9mm.

 

So I do not know how thin is too thin from personal testing, but I do know how flexible is too flexible, and I like them stiff.

 

Cue the ‘thats what she said joke’

6

Are those the 3D printed fins?  I haven’t tried but a layer or two of carbon on each side would stiffen it up some.  Not sure if epoxy sticks to the 3D material though(?)

7

Yes they are, and epoxy does stick OK to good, but more so when the slight porosity of the material is  enhanced. I glassed over one  fin whose filament had layer separation issues. and consider it in the top 2 fins i currently have and have ridden.

 

I bet the mad scientist is plotting how to make even thinner and stiffer fins. 

8

The best thing I found about thinner fins is the top speed, there’s almost no drag from the volume or foil. I believe that a thick fin needs to be foiled and the foiling creates drag even in a straight line. As all the fins point in a different direction it’s likely all fins are dragging and constantly slowing the board.

 I used to make them from veneer and Carbon / glass but I’ve made them from all sorts of plastic, wood and specialist Aluminium.

 The plastic ones are 6mm thin and the aluminim fins are just 2 mm. That’s exceptionally low drag in a world of 10 mm fins.

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9

I found that thin fins (6 mm or so leading edge foil) tend to cavitate much easier, making them less reliable and slower in the long run.

Maybe just me.

10

No, it’s not just you.     You are spot on.       A thick foiled fin, is far superior, in the dynamic environment of a wave.      Still water?     Not quite as much.

11

No, it’s not just you.     You are spot on.       A thick foiled fin, is far superior, in the dynamic environment of a wave.      Still water?     Not quite as much.

12

My experience as well. I know that despite the photo of Greenough grinding on stainless steel, his edge board kneeboards and sailboards most often used very thick foiled fins. Maybe he used the metal ones on sailboards for flat water running?

13

Maurice Cole who  builds Ross Clarke-Jones’ tow boards swears by the C-Drive fins which has a standard base but a real thin chord and thin sweep that he maintains is the best for really high speeds.

I think that the thicker fins are fine up to a point but when you’re looking for the maximum speed, not necessarily  most manouverable, then thinner fins are proven to reach those highest speeds. It’s much like the minimalist size of tow boards themselves and how much faster foils are than a standard surfboard.

 Up to a point all the classic fin designs work but at the highest speed they can’t compete as their drag coefficients are always higher.

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14

Too thin is if the fin is not stiff enough to avoid wobbling / buzzing / humming when you drop down the biggest wave of your life and go faster than ever before. 

Too thick is if the fin slows you down too much while you are paddling for the biggest wave of your life, and thus makes you miss the wave. Or if the thicker fin wears you down while paddling against a sweep to reach and hold position, and then you have more noodly arms by the time your wave arrives. 

For the same reasons, I think any more than one fin is too many. 

15

MrMik, too much cant and too much fin area like a bad done bonzer slow down a lot the paddling power

16

No issue if using one fin only! I like it simple.