Then we all agree the 13% ratio all the way is the best. A bit of critical thinking. We say that straighter leading edge and an outline like the Wayne Rich Harmonic or the fcs H2, 3... Fins is more efficient. Why is not everybody using this outlines? A curved leading edge is less efficient but should be better for something else. If not peoøle wouldt choose that outlines. Better turning or... you name it. Is my point correct?
These more efficient outlines with reduced tip chord length are probably not being used widely for a few reasons.
Anyone spending money tooling up to make multifins will be taking a risk on a fin outline that surfers are not used to seeing. The high performance shortboard generic fin outline has been with us for a long time and most surfers just assume that it is the optimal outline and would be risk averse to spending money on anything else. Although FCS are edging towards fins with reduced chord length at the tip with designs like the H2 and H3. In fact I believe the H2 was designed in conjuction with a naval architect, which would explain why its outline is what it is. You will see more variation in hand foiled longboard single fin outlines because there are no tooling costs involved.
Also, as gdaddy has alluded to in this thread, these less efficient outlines might actually be what surfers want, despite the fact they have more drag. The additional drag created by long chords lengths at the fin tip might create a feeling of control, or hold, or drive. Terms which are difficult to qualitatively define, and don't have a lot of scientific meaning, but are important to what a surfer wants to feel when turning.
I started foiling this one. Using 13% /2 for thicknes and different foil than usual for my twins. Really looking forward to compare it with the thinner ones
I am also not a professional airfoilologist, but have learned a lot since I started designing fins in CAD to be cut out with a CNC router. In my opinion its a lot less intuitive, you can't sand until it feels good, but it can be more data driven. I start with an fin outline. Then, theoretically based on conditions I plan to surf in but realistically picked on suggestions by other swaylockaholics, I pick an airfoil with appropriate lift, stall, angle of attack properties. My chosen outline and airfoil dictate how thick my fins are and where the thickest part of the fin lies. This approach also allows you to use different airfoils along the height or sweep of the fin to almost tune the fin to how you want it to perform. Finfoil is a great resource even for hand made fins. I previously used finfoil's printed contour map to hand shape a few fins.
All of that being said my fins all come out on the thicker side, 1/2"-3/4", and I think they all surf well. I made a quad set for FCS boxes that were 1/2" at their thickest, but I haven't glassed or surfed them yet.
I think part of the equation includes the amount of energy and speeds involved in various conditions. How much drag do you want? You will *want* to run slower and apply more rider input in slower conditions whereas in fast conditions that becomes a big problem. If you're using a fin cluster as your motor then you're using them differently than if you're using a board's rail line as your motor and the fin is there primarily to provide hold, stability and control.
I don't longboard, but I see the function and use of a D-fin on a noserider to be distinctly different than a keel on a windsurfer or a thruster cluster on an HPSB.
Hi, thanks for bringing this very interesting topic up. The 13 % thickness... i have been playing a bit with finfoil.io and i have to say these thick foils look different.
One thing.. when are fins considered to be a half foil? Only when they are flat on one side? A lot of fins now incorporate a inside foil, from what i understood these should be thicker too, right?
In a twinzer or split keel set , would it make sense to have a thick fin in the front and "leaner "fin in the back ?
Hi, thanks for bringing this very interesting topic up. The 13 % thickness... i have been playing a bit with finfoil.io and i have to say these thick foils look different.
One thing.. when are fins considered to be a half foil? Only when they are flat on one side? A lot of fins now incorporate a inside foil, from what i understood these should be thicker too, right?
In a twinzer or split keel set , would it make sense to have a thick fin in the front and "leaner "fin in the back ?
Side fins which are flat on the inside are half foils, so 6.5% thickness to chord length is what suits them.
If your side fin has convex foil on the inside then 13% is ideal drag wise. Concave inside foils on side fins however is another story. 6.5% would probably be best for them I would think.
Please remeber that all of this is "ideal", and for example the drag inherent in a thruster type fin set up itself is magnitudes greater than any drag reduction you might achieve by impmenting the 13% ratio on all the fins. Twins and quads will benefit more, and a single fin will benefit the most.
Any advice from me on particular fin set ups, beyond these basics I've outlined would be purely speculative, and uninformed. There are others here with much more experience on these matters from a practical point of view than me, who may be able to help.
I'm not a hydrodynamicist but I do recall reading about two good surfers who did some experimenting with speed foils. George Greenough and Nat Young come to mind and both guys have at one time or another reportedly used thin foils for maximum speed... GG on a windsurfer and NY on a surfboard at a world contest where he said he added bondo edges and foiled his fin thinner to maintain control and drive in unexpectedly big conditions. I have a photo of GG from a magazine where he is shown foiling a fin cut from stainless steel panel - thin but stiff... again, on a windsurfer where change in angle of attack would not be as important as in surfing in general day to day conditions.
I believe, as has already been stated in this thread, that some elements of fin foil design may have been compromised to some degree based on ease and expense of production.
These more efficient outlines with reduced tip chord length are probably not being used widely for a few reasons.
Anyone spending money tooling up to make multifins will be taking a risk on a fin outline that surfers are not used to seeing. The high performance shortboard generic fin outline has been with us for a long time and most surfers just assume that it is the optimal outline and would be risk averse to spending money on anything else. Although FCS are edging towards fins with reduced chord length at the tip with designs like the H2 and H3. In fact I believe the H2 was designed in conjuction with a naval architect, which would explain why its outline is what it is. You will see more variation in hand foiled longboard single fin outlines because there are no tooling costs involved.
Also, as gdaddy has alluded to in this thread, these less efficient outlines might actually be what surfers want, despite the fact they have more drag. The additional drag created by long chords lengths at the fin tip might create a feeling of control, or hold, or drive. Terms which are difficult to qualitatively define, and don't have a lot of scientific meaning, but are important to what a surfer wants to feel when turning.
Many thanks for that observation/information lemat.
I'm sure the mast manufacturers have done their homework.
Thank you so much for all of this good information.
I started foiling this one. Using 13% /2 for thicknes and different foil than usual for my twins. Really looking forward to compare it with the thinner ones
Collage_20211027_195145_edit_867705118104576.jpg
I am also not a professional airfoilologist, but have learned a lot since I started designing fins in CAD to be cut out with a CNC router. In my opinion its a lot less intuitive, you can't sand until it feels good, but it can be more data driven. I start with an fin outline. Then, theoretically based on conditions I plan to surf in but realistically picked on suggestions by other swaylockaholics, I pick an airfoil with appropriate lift, stall, angle of attack properties. My chosen outline and airfoil dictate how thick my fins are and where the thickest part of the fin lies. This approach also allows you to use different airfoils along the height or sweep of the fin to almost tune the fin to how you want it to perform. Finfoil is a great resource even for hand made fins. I previously used finfoil's printed contour map to hand shape a few fins.
All of that being said my fins all come out on the thicker side, 1/2"-3/4", and I think they all surf well. I made a quad set for FCS boxes that were 1/2" at their thickest, but I haven't glassed or surfed them yet.
I think part of the equation includes the amount of energy and speeds involved in various conditions. How much drag do you want? You will *want* to run slower and apply more rider input in slower conditions whereas in fast conditions that becomes a big problem. If you're using a fin cluster as your motor then you're using them differently than if you're using a board's rail line as your motor and the fin is there primarily to provide hold, stability and control.
I don't longboard, but I see the function and use of a D-fin on a noserider to be distinctly different than a keel on a windsurfer or a thruster cluster on an HPSB.
Hi, thanks for bringing this very interesting topic up. The 13 % thickness... i have been playing a bit with finfoil.io and i have to say these thick foils look different.
One thing.. when are fins considered to be a half foil? Only when they are flat on one side? A lot of fins now incorporate a inside foil, from what i understood these should be thicker too, right?
In a twinzer or split keel set , would it make sense to have a thick fin in the front and "leaner "fin in the back ?
Side fins which are flat on the inside are half foils, so 6.5% thickness to chord length is what suits them.
If your side fin has convex foil on the inside then 13% is ideal drag wise. Concave inside foils on side fins however is another story. 6.5% would probably be best for them I would think.
Please remeber that all of this is "ideal", and for example the drag inherent in a thruster type fin set up itself is magnitudes greater than any drag reduction you might achieve by impmenting the 13% ratio on all the fins. Twins and quads will benefit more, and a single fin will benefit the most.
Any advice from me on particular fin set ups, beyond these basics I've outlined would be purely speculative, and uninformed. There are others here with much more experience on these matters from a practical point of view than me, who may be able to help.
Thanks!
I'm not a hydrodynamicist but I do recall reading about two good surfers who did some experimenting with speed foils. George Greenough and Nat Young come to mind and both guys have at one time or another reportedly used thin foils for maximum speed... GG on a windsurfer and NY on a surfboard at a world contest where he said he added bondo edges and foiled his fin thinner to maintain control and drive in unexpectedly big conditions. I have a photo of GG from a magazine where he is shown foiling a fin cut from stainless steel panel - thin but stiff... again, on a windsurfer where change in angle of attack would not be as important as in surfing in general day to day conditions.
I believe, as has already been stated in this thread, that some elements of fin foil design may have been compromised to some degree based on ease and expense of production.
greenough stainless.jpg
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