Hey Sways,
Fins run the gamet from ompletely rigid (polycarbonate) ~ al la Horan/Lexan Starfin to a thinned out high profile super flexible polyester/glass Greenough Stage IV.
We live in a media that sports all kinds of flexiblity claims for performance short boards, funboards, & longboards
What’s you take on this picture? Where does fin flexibility and speed of recovery (resilience) fit into the fin performance picture?
Gone Surfin’, Rich
Hi Rich -
One of the flexiest fins I’ve tried (i.e. Harbour boomerang/banana? fin) seemed to give a little too much for my style of surfing. I had the sensation of it losing thrust on the bottom turn followed by a “rebound” effect that twisted me up on the shoulder a couple of times. Obviously, some guys like it - I see a lot of them on longboards. I’ve also seen some stress cracking in the narrow section of the fin on some older ones.
One of my favorites in small to medium surf is a Liddle flex fin. It’s a more vertically oriented outline with not much tip area. It seems pretty loose with a bit of springiness and allows easy rail to rail transitions.
I also keep a couple of basic stiff glass blades for bigger conditions on the same boards.
I guess that’s a simplified version of my experience from really flexy to really stiff, really raked to really vertical… a place for each in different conditions.
Well for me, I tend to flex the fin according to the rail shape…the harder the rails, the stiffer the fin flex. On tri fin set ups I always have the centre fin pretty stiff, and vary the flexes on the side fins. I do not like thinner fins, and any flex is in the tip. I guess it depends on how you surf as to whether you retain speed in a turn or not…
As the others said, the variety of board length, riding styles and wave conditions dictate personal preferences.
I find the flex I like similar to board flex. Quite stiff at the base but with uniform flex towards the tip.
I feel I need a certain amount of rigidity to get the job done, too flexy to me felt sort of saggy, if that’s a description. The secondary drive people talk about getting from a flexy fin I found too unpredictable.
And yet too stiff felt like it needed to be ridden to precisely, didn’t leave as much room for spontaneity. Not as forgiving.
I haven’t ridden a board over 7’8", most between 5’10" and 6’7", all what I guess you would call modern performance designs. In the end, after many years of trial and error, I pretty much used the same fins in each board.
I was watching pbs the other day and there was a show wherein a team was developing a ‘crab-like’ automated robot designed to sweep the ocean floor for mines.
An interesting statement was made by one of the designers/scientists along the line of “we don’t always have to follow nature to a ‘t’”; referring to the robots six legs (as opposed to more in a real crab" and fewer joints in each robot leg as well, allowing it to still accomplish all its tasks while still being less complex than a real crab; it even could do thing a real one couldnt like get flipped and just tweak its legs the other way and keep going instead of having to right itself.
Maybe not relavent but got me thinking along the lines of nature is the main (and totally logical) influence (as you have said/known who can deny the millions of years of evolution!); but we still might end up falling on the trial and error of strange imaginative ideas that dont resemble known existence (??)
maybe loehr is right, design has just about run its course we’re down to materials…or are there still millions of combinations out there that can render known models/surfcraft obsolete??? maybe refined materials open up and make new/once thought infeasible designs possible to excel??
Wonder what will happen when, like the f 16, the craft has greater capabilities than the pilot can physically endure
only a combination of time and hard work but mostly luck will tell i suppose??..just some rambled thoughts
rich curious as to your current thoughts on paddle fins
would a 1/4" diameter solid round (or rain droppish shape curved leading edge) have more drag/leave more turbulence than a standard 3/8" thick 4-6" long “base” of a well-foiled fin? just talking bases, not whats past 3-4 inches down. Yes a naive question, any thoughts anyone?
fin thickness changes two factors, mainly. The first is sensitivity - both drag and lift increase more quickly with small angles of attack in thin fins. And the lift:drag ratio is better with thin than with thick fins.
The other factor is maximal angle of attack sustainable. Thin fins stall at smaller angles. Whether this is relevant depends on whether your application is sensitive to fin stall or not. In other words, as design criteria, you want to use as thin a fin as possible while not stalling.
These criteria assume you’re using a fin that is going to experience positive and negative angles of attack equally -ie: a center fin.
Fatter fins in the middle will not drag as much for small angle of attack changes, but will also have less lift than thin fins at every angle of attack up to the stall angle.
When you play with assymmetric fins as rail fins you alter a lot of factors - you are essentially tweaking one parameter, and moving the “best fin” around in a multidimensional space. The problem is you’re only searching in one dimension. You need to play with toe-in as well, at least, as well as the degree of assymmetry and the thickness. The best rationale for thick fins is that they are much more easily made stiff enough, and there are a LOT of fins out there that are not stiff enough.
Back to Halcyon’s point, I’ve used rotating fins in my single fin boxes. The fin is essentially infinitely stiff, but turns in toe-in angle around its leading edge. Matching the stiffness of rotation to the riding conditions is essential. The forces on the fin change by an order of magnitude if you go from knee high waves at 5-8 knots to 25 knot double overhead plus, and it should be no surprise that the best rotational stiffness changes by a similar amount. Softer finbox for slower waves, stiffer finbox for bigger waves. With time the rider gets to ‘know’ the stiffness the same wave a longboard skateboarder knows how stiff his trucks are. I’ve never been satisfied with the rotational stiffness at both head high and double overhead. Or, waist high and overhead - it’ll always be wrong for at least one of the sizes. Flex fins are pretty similar. There is a performance boost available, but you need to be dialed in to the conditions.
right on…a lot of the stuff u said has made sense to me - liddles thinner fins with the wide point further back being faster, greenough thicker more towards leading edge having more lift…
those rail fins i made on my last board are pure carbon epoxy and are like 1/8-3/16 thick…super flexy but the blade remains pretty stiff
you know what trips me out is the guys that tune the fins perfectly to their hull/rails. Like that liddle hull…you look at it and its pretty big compared to what i usually ride, and it has this littlish fin foiled reeeeally friggin thin and flexy at the tip, and ran waaay up on the board…and the thing has INCREDIBLE drive.
but what really blows my mine is how greenoughs velo was tuned so sweet his fin would come out of the water, and he would still be driving all rail and it would be in control as the fin re-entered…just friggin mind blowing.
hows the mechanical feasibility of getting a weight friendly flex box for sidefins goin?
edit- oh yeah and my initial question wasnt about lift but just drag…would dragging a 1/4" dow through the water have the same, less, or more drag, than dragging a 6" long 1/4" at thickest foil with, say, an average placement of the thick point for a popular single fin. Just the drag on say 3" depth of those specs (no rake or outline changes on the foil in question)
2nd edit- holy smokes did some reading there are too many factors to esablish a base as everything changes so much…saw one graph where spheres have less drag then a cylinder of the same diameter, but at a certain speed or input energy threshhold, it switches and the cylinder becomes more efficient! heavy stuff, too much for my peabrain-
sorry for the gibberish rich, carry on with your thread!
hey rich ,
in the last 6 months ive gone through another one of those intensive periods where i end up trying heaps of different stuff only to confirm what i already knew , but can at least have a deeper appreciation of why and how to add to the intuative feelings i already had …
ive been through a series of fins from thick flexible ones , thick stiff ones , thinner (not blakestah thin) flexier ones and thin rigid ones …
using as a sandwich or filler , core cell , 80 d cell , 60 d cell , 4.5mm ply and 9mm ply …
fabrics were standard e glass 2, 4, and 6 , 200 gram twill weave carbon , hessian , and lastly cotton , couldnt tell you the weight …
plus tried 2 different epoxies , one with a longer pot life , slightly lower hdt, and a lower barcol hardness which gave it a slightly rubberyer feel , 2 polyesters , standard lam res and a gp resin , also tried tooling 2 part liquid urethane …
regardless of flex , , one common denominator was the fins ability to spring back if it did bend , all the floppier softer fins just didnt cut it in , fast sectiony waves that required quick spontaneous manouvers …
the stiffer fins respond way quicker as no energy is lost while the material loads up ,
in certain soft waves the floppier fins still worked fine as long as you had plenty of time to line sections up , and held nice clean arcs that didnt change to quickly in intensity or tightness …
all the stiffer fins gave instant response time (blakestah will like this) even the thin stiff fins responded instantly , but just wasnt as smoothe and fast out the end of the turn , and tended to stagger or make me do my fast drawn turns in stages washing off a touch of speed with each stage …
so many variables to mention , and give details of each combo …
but in a nutshell the light stiff well foiled fins were the winner …
none of the foam filled fins could really handle serious direction changes without some lag , except some carbon/eps combos which i got super stiff …
so many other possibilities as well , because of the board/fin combos …
it comes down to energy transfer …
energy transfers quickest through something that is stiff with a low density …
i started thinking that the weight of the solids had something to do with them feeling slightly spongier or not quite as responsive , but now im convinced that energy wont transfer through the higher density fins quick enough …
your fins are really at the extreme end of your reach , as far as your ability to feel whats happening far away , almost like an extension of your body …
if you were blind and had a long stiff cane im sure you would be able to define more detail at the end of the cane , then if you had a soft rubbery one…
ive always believed that a board should get proportionately stiffer the further away it gets from you , i think that same philosiphy applies to fins as well as an extension of the board , that every part of the board should get stiffer the further away it gets from your center of gravity/mass to give you the most far reaching sensitive feeling of whats going on around you …
dolphins ride the wave in the power zone , if the power of a wave is deeper down , then it stands to reason we can harness some of that with fins that transfer that energy back to us in a more efficient way …
reaching in past the turbulent boundry zone to the clean green water …
i really think tom would agree with the lighter stiffer fin giving more sensitivity as opposed to the heavier stiffer fin …
but i will make that point again that if you have 2 fins with the same stiffness , but one is heavier than the other , the lighter one will respond quicker , not because of lightness or weight but because energy can transfer quicker through a lower density …
also even if 2 fins seem to have the same weight and stiffness , depending on how the molecules are linked , will determine how direct the energy can travel …
the lower the hdt the quicker a polymer based material will reptate …
those thermo softening style polymers and resins with lower heat distortion temperatures dont seem to feel as lively , even tho they feel similar in your hands when trying to bend them …
if making a standard lay up fin it would make sense to put a layer of carbon in the middle , that way as the fin is foiled , even tho the tip gets thinner it also gets proportionatly stiffer in comparison to the rest of the fin , and when doing side fins , putting the carbon on the flat side …
right now im loving my timber carbon combos …
regards
BERT
Dear All
A while back some people were talking about basalt fibre. Did anyone try it in fins? Seems like a safe alternative to hand foiled carbon - apparantly the basalt fibres break into sections that are too long to cause irritation.
I have some samples of the stuff, There isn’t anything they sent me that would wet out very well at all.