colas said..

Johndesu said..
Also I have just seen the "Quantum fin" on line (not yet available I think) which you might be interested in looking at colas :-)

Interesting, especially the video where he explains the evolution of the design. Note how he is progressively tending to a C-Drive outline :-)

Anyways, I think his "scientific" explanations are bull****. What he discovered is that moving the center fin of a thruster close to the sides loosens the ride.
Or you can get your "quantum" setup by just moving the sides aft and center front on a thruster setup. I loved this setup on a thin 9'11": insane pivot and looseness, and the lack of drive wasnt really an issue on a board with long and thin rails to rely on in the size:



And note that you can add another FCS box to get 3 positions for the center fin: (one one the ideas I am proud to have given to Gong):

Yes I understand all that but what about the idea of the lift that is explained and that the fin produces and also less drag - do you think that it is a valid point? I am interested in what you think?:-)

colas said..

Johndesu said..
Yes I understand all that but what about the idea of the lift that is explained and that the fin produces and also less drag - do you think that it is a valid point? I am interested in what you think?:-)

If there is lift, there is drag.
There is no motor in the fin, the force for the lift must come from somewhere.

About the lift, the real lifting is done by hydrofoils. Picture an hyrofoil with not enough force to lift the board out of the water: it will just create drag. The benefit is only when the hull leaves the water and its resistance is totally zeroed.

I stopped the vid when he began to say that the force of the fin was pulling forwards...

Note that his fin may very well work, despite his "explanations". This would not be the first time something would work in practice without the inventor knowing why. Especially in surfing...

Yes I see what you mean - it is interesting to think about it - thanks:-)

Tardy said..
big test for me today ....only 3 foot waves but steep ...using the after market fin i did notice ,,,they felt
very draggy and slow ...so when i got home ..i compare them with the originals .....and yes a lot wider ...even though the same shape and size ...
so...a loss of speed ...and liveliness .....

the fins are too fat...they will be getting a good sanding ...

so there are good fins and average ...customising...is the go ...

Yes it is good to sand your fins a bit, I also always sand the sharp edge so it is not so sharp :-)

Just had a amazing surf ,as a quad set up only 2-4 foot .....the rear fins I used had slight flat edge and quite a stiff fin .with honey comb ,claiming
they are light fins ...as if it makes any difference really they are that small the extra weight would not matter .

question ...are flexy fins better ...in some circumstances ...

i think I have found the perfect size now for my board .and semi flex..

after sanding a few sizes down ....some I made ..too small , they where too sketchy.

Ok thanks ...stiff fins are working ... I must say it s great to finally find a good combo of fins that work .
it makes surfing so much more enjoyable .what you have told me has just verified my thoughts on fins .
I'd have to say my board has increased in performance by 30%.. Stoked.

Jeroensurf said..
With the windsurf fins K4 claims the flex stores a bit of the energy bounching back and help to accelerate when you take the pressure of them.

This is a classic bull** pseudo-scientific claim. The stored energy would be too minimal to be felt.

What is actually happening is that the fin avoids stalling by "spilling up" the extra power while maintaining the laminar flow. This means that the fin will continue working (providing lift without too much drag) during all the turn, whereas a stiffer fin will stall under pressure and slow the board mid-turn.
So will definitely feel an acceleration with a good flex fin compared to a standard fin.

It is strange that K4 said this, because the windsurfing world have been exposed to these phenomenon for a while with the revolution in flexible sails that happened ~ 20 years ago

I ride a 7.10 x 27.5 and have been trying plenty of different fins this last year... I have settle on fcs2 performer XL sides with a medium centre for small waves and mediums all round when it gets bigger..
I got to talk to Justin Holland in WA at the nationals and he said he uses bigger fins in small waves and much smaller in big stuff...
I'm settled in my fin choice for now ...i went back to quad for a session after not using them for over 12 months and hated them....thruster for me all the time from now on....

Tardy said..
Question.do narrower tailed board require or like bigger fins or smaller .

I use smaller fins on boards with rear rails that dig deep in the water, to let the rail do the grip work and the fins just stabilize.
There are mostly longer, gunnier shapes

Loz79 said..
I ride a 7.10 x 27.5 and have been trying plenty of different fins this last year... I have settle on fcs2 performer XL sides with a medium centre for small waves and mediums all round when it gets bigger..
I got to talk to Justin Holland in WA at the nationals and he said he uses bigger fins in small waves and much smaller in big stuff...
I'm settled in my fin choice for now ...i went back to quad for a session after not using them for over 12 months and hated them....thruster for me all the time from now on....

Hey Loz .7.10 and 27.5 is a small board ,I reckon 3 fins would be plenty .It is a different riding style to a Quad .
i too like the thruster feel.you can do snappier turns .
quad turns I feel are more dragged out .but I like the floaters which quads are good at .

this all depends on board shape too.
eg..I have a 2016 7.0 Raptor ..they first came out with a rear fin box ,then the later ones just Quads ,they ditched the box .
I guess they reckon quads where the go for this shape ..it's a loose little mother .most you can paddle is 3-4 on one side .

colas said..

Jeroensurf said..
With the windsurf fins K4 claims the flex stores a bit of the energy bounching back and help to accelerate when you take the pressure of them.

This is a classic bull** pseudo-scientific claim. The stored energy would be too minimal to be felt.

What is actually happening is that the fin avoids stalling by "spilling up" the extra power while maintaining the laminar flow. This means that the fin will continue working (providing lift without too much drag) during all the turn, whereas a stiffer fin will stall under pressure and slow the board mid-turn.
So will definitely feel an acceleration with a good flex fin compared to a standard fin.

It is strange that K4 said this, because the windsurfing world have been exposed to these phenomenon for a while with the revolution in flexible sails that happened ~ 20 years ago

I,m a nurse and although it interst me a lot I have no hydronamica or engineering background so I guess i,m not the one to call something bull**** nor am the one to say something else is right. I guess his argument as well yours are pretty difficult to prove as right and maybe you two are both right.As far as I can judge finmaking is still more an craftmanship as science.Anyway, what do I know from trying and feel due trial an error is that they seem to work really really good in some conditions: steep but not too fast waves. In really fast waves/ high speeds I prever a stiffer set up. My GUESS is that under the high speeds softer fins might twist at the base under pressure and the faster passing waterflow where a stiffer fin do,nt. but then again, its just a guess.

As far as me is told by some pretty big brand windsurf fin designers I met ( Pio from MFC, Rik from Maui Ultra Fins and Steve from K4) / discussed stuff with through the years, the basics are copying nature (dolphin fins) and playing from that starting point and from there mostly trial error and a lot of guessing.CFD: Computarized Foiling Dynamics isn,t that old and the NACA profiles we used in the past not suitable because wings act and are calculated on different speeds.Again, I know a lot more about bodies as about boards and stuff but where you get irritates when people mix up things, I get triggered by people burning Ideas based on what sounds like an asumption as well? I guess as much as they can,t prove there claim its as though to proof there claim is wrong and the rest seems to be opinions based on FEEL and ideas. :)

On the bit lighter side: We don,t have that much of quality waves in Holland but today was pretty awesome with shoulder to just overhead high clean glassy pretty fast waves and I was just able to squeeze out an sundowner session :)Even with my I don,t-know-what-kind-of-profile-but-they-seem-to work-okay-standard-Starboard-fins under my Airborne8.8 and the fact is was minus 2 celcius..it was AWESOME :)

Johndesu said..
Can you please explain and give some examples because it interests me greatly, - I am still experimenting with different fins & on different boards. Also I am still looking for some H3 fins (I recently lost a side fin out the reef:-)

An example is the inside foil of side fins. There is no question that an inside foil is "better" for efficiency (more lift less drag), but in actual surfing use flat-sided side fins have their merits: they may be slower but may give more control, depending on the board, rider, conditions.

I see that Future for instance even mix the foils: inside foil at the base for efficiency, but flat foil at the tip to keep the feeling in turns for people used to flat inside foils. Future has a lot of good info about fin design, btw.

You can find a lot of good info at: forum.realsurf.com/forum/viewtopic.php?t=3492

I read once an interview abut the design of the H2 fin I can't find again. Basically, FCS hired a (non-surfer) naval engineer to design the "best" fin by reproducing the movements of a surfboard in an observation tank, starting from some known profiles. The result was the H2 fin, but it proved not so great in actual tests by surfers, so FCS now uses tank data as one input among others (riders feedback).

On the spare H3, contact your FCS shop, they can provide spares normally.