What is the formula to find the proper thickness for any giving fin? I read somewhere that in most fin systems including old style box’s the fins are not the proper thickness for the shape/size of the fin according to proper hydrodynamic principles. The example was giving of those hollow Karl Pope fins that are twice as wide at the wide point than the slot in the fin box. Obviously Mr. Pope has a formula he used to get the thickness he desired for any size fin and he must of had a reason why he thought they should be so wide. I seem to remember seeing pictures of a fin shape formula where all this was laid out…especially the part about the widest point of the fin and where this wide point is placed in relation to the leading and trailing edge of the fin. Anyone?
"Obviously Mr. Pope has a formula he used to get the thickness he desired for any size fin and he must of had a reason why he thought they should be so wide."
Reynolds Yater designed the Hollowfoil fin.
Regarding "CORRECT" thickness... it's likely variable depending on what board, wave and rider is involved.
Thinner is faster but more likely to track. Thicker is easier to pivot and allows greater angle of attack while maintaining laminar flow on both sides of fin.
There’s a formula around here somewhere on the relationship of chord length to thickness
like most surfboard thingies there’s trade-offs, as John said
naca foils suggest 8-12% of the length is a good number. It is however up to the individual. Way too thin fins also have tendency to cavitate.
measure your nose at the bridge.
Fins should never be thicker than your nose.
unless you have an experimental permit from
authorities to have a nose + fin. All boards
so permitted must have the permit glassed
on the bottom 9’’ forward of the trailing fin.
when you are caught without a permit
you can be jailed,car confiscated,
board confiscated all hair removed
from your body with an razor that shorts out.
if you do make a board with an excessive
fin component thickness,hide it when men
AND WOMEN from the surf police
are walking the strand…!
…ambrose…
ask any perch
how to set up fins
to match theirs.
perch always out perform
other boards for stand surfing.
That wasn’t helpful…or funny.
now that
was funny.
…ambrose…
when in doubt copy .
understanding
only a fool
has the courage
to do things wrong
and learn the limits
first hand.
That WAS funny and clever. When in doubt, copy, is good advice. Having the courage to do things wrong and learn the limits is part of the fun of doing it yourself. Mike
There are ''clues'' in nature. Certain surfers, in the early 1950's, paid attention and used the information. The answer has also appeared in discussions on Swaylocks, in the past. The answer also appears in this thread. Do your own homework.
''IT IS ONLY WITH UNDERSTANDING, THAT YOU KNOW.''
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"There are ‘‘clues’’ in nature. Certain surfers, in the early 1950’s, paid attention and used the information. The answer has also appeared in discussions on Swaylocks, in the past. The answer also appears in this thread. Do your own homework. "
So I shouldn’t ask for insight I should just figure it out myself? What’s the point of the forum then?
I never asked who invented the hollow fin but only why Mr.Pope’s fins are so wide and why his fin is so different from other box fins of the same size. His fins thickness is over 14% of the base length…more than the 8 to 12% HANG20 suggested. Here in PICTURE #1 are two fins with the same template and base length. The Pope fin is almost an inch wide and the Rainbow fin is just over 5/16 wide. That puts the Rainbow fin at 5.5% of base length and the Pope at 14.5%…again far outside the 8 to 12% suggested. So what was Pope after that made him build this fin? More pivot, better turning? What did he think was lacking in thinner fins?
My main question was asking if most fins today including box fins and all fin systems fins are the right thickness for the size of the fin. (And when I say RIGHT I mean right within whatever rage is accepted as good) The 5/16" thickness of most fins today seems right for a 4.5" fin base but as any fins’s base gets longer the fin should get thicker right? Here in PICTURE #2 is a wide range of box fins of all different sizes and base lengths yet every one of these fins is around 5/16" thick. Why are all these fins the same thickness? The largest fins with base’s over 7" should be much thicker even if I used the 8 to 12% suggested. So whats the deal? Is it just cheeper and easier for fin makers to make the fin as thick as the box… because that’s my guess. Does anyone out there besides Pope make fins (especially larger box fins) thicker than this accepted 5/16th of an inch?
My last question was about the placement of the thickest part of the fin in relation to the leading and trailing edge of the fin. On the Pope fin with a base of 5-3/4" the thickest point of the fins foil is 1-3/4" from the leading edge. Just over one third of the total base. Can that be adjusted front or back and to what effect? Like most of these things I know someone had already tested all of this and I only want to understand why the accepted placements have been accepted. All my other large box fins have no obviously discernible thick-point and most of them seem to be the same thickness (5/16") for most of the fins base length. Most of my box fins don’t have that foil shape you see in fin foil drawing or that you see in the Pope Hollow fin (PICTURE#3) This fact is making me again think that most box fins are production made without much concern for the proper foil for the size fin being made.
Surf your board with the Rainbow fin for several sessions, and then surf it with the Pope fin IN EXACTLY THE SAME POSITION, and all will be revealed. Hint, pay close attention to what happens on a hard backside cutback. I went to thick foiled fins in 1960, after a discussion of the topic with Phil Edwards. My own ''happy range'' is 10% to 15% of chord. In general I end up with about a 12.5% ratio. Those ratios are for symmetrical foils only. Try not to be quite so demanding, when asking questions. Because I know, do you consider me a fool? Go to the NACA site, lots of insight to be gained there. Pay attention to the discussion of laminar flow foils.
Not sure where I demanded anything but thanks for your help.
[quote="$1"]
Not sure where I demanded anything but thanks for your help.
[/quote]
It was the tone that I was reacting to. The real problem is that I'm probably just old and cranky. Hope I was not too offensive.
Hey Bill no problem. When I saw your signature “Shaper since 1958” that’s just what I thought, “Oh he just old and cranky.” I’m only 41 and I’m already pretty cranky so you have a lot more of an excuse then I do!
Bill
[quote="$1"]
That wasn't helpful...............or funny.
[/quote]
i thought it was both =)
''Surf your board with the Rainbow fin for several sessions, and then surf
it with the Pope fin IN EXACTLY THE SAME POSITION, and all will be
revealed. ‘’
Thats what I would have told him.
Let us know after you do it.
Howzit Bill, As I look at the bases of both fins I don't see a metal pin in the Pope fin like the Rainbow has so how can you use them in the same box. I do see the pope screw hole is in front and the Rainbow's is in the rear but that's no big deal. Aloha,Kokua
[quote="$1"]
Howzit Bill, As I look at the bases of both fins I don't see a metal pin in the Pope fin like the Rainbow has so how can you use them in the same box. I do see the pope screw hole is in front and the Rainbow's is in the rear but that's no big deal. Aloha,Kokua
[/quote]
The Pope fin has front and rear tabs. They use a small square plate. Or the FU plates can be trimmed to fit in the smaller space under the tabs on the Pope fin. So, you drop two plates into an FU box, and you are in business.
Howzit Bill, So the Pope fin has 2 screw holes and you put 2 screw plates in the box, I can see how that would work. Thanks for the answer.Aloha,Kokua
Ya I thought it was weird when I bought it but the fin came with two screws plates. Two of the small square screw plates and not the bigger rectangle ones because they wont fit. I guess because it’s made from cheap plastic the pin in front system would probably break the fin base… especially if you hit something. I used it allot on a 7’ G&S egg I had but never did do the comparison of the two fins (I should have). Then the fin started to fill up with water when I used it and I could never find where the crack was so I stoped using it. I’d do the test of the two fins now but I don’t have a good board to use the fins in. I’ll try to find one soon.