Thick fins vs. Thin fins

Not too much time to post at the moment, but I have been lurking on this thread. I’m the guy (or one of the guys) who told Mark about the audible squeaking / ventillation issues with the set of 3/2’s (with the hatchet center fin). But I’m not the guy who did the Spicoli impression :wink:

I’ve posted about this phenomenon before, both at sway’s and at the surfermag forum page, and have experienced it a few more times since then, so I know it is not all in my head. I pretty much ride the 3/2 vectors in overhead+, hollow surf because of their barrel-beating speed. The fins seem to maintain very high top speeds (faster than with “normal” fins, for sure) and drive when ridden with rails very engaged, BUT I have experienced the squeaking/ventillation issues under two circumstances (which are almost polar opposites!):

  1. When backing off of the engaged rail and evening out the pressure so the board is riding fairly flat on the water’s surface in order to cover a lot of ground to connect over a relatively flat section of the wave. This is usually accompanied by a percievable lifting sensation and a little loss of control that sometimes passes (but not always).

  2. When coming off the bottom turn in a section that is standing up and begging for a full-rail off-the-top hack… executing the bottom turn by backing pressure off the front foot and putting almost all of it on the tail to do a tight, quick re-direction off the bottom and up at the lip, approaching it from an 11 or 12 o’clock track. I can usually break up the squeak/ventillation with a quick wiggle of my back foot at the ankle, but who wants to do that when the surf is dicey?

I’m about to take receipt of a new board equipped with RedX and will be putting Tom’s Next Generation X 2’s through the paces on that board in the hopes that those thicker fins give comparable speed but prevent that off-the-bottom stall that the Future’s 3/2’s are doing. Can’t wait!

“Remember that scene in the movie Without Limits where track coach Bill Bowerman describes to Pre how taking a 1/4 oz off the weight of a running shoe over the distance of the race lowers the total amt of weight a runner lifts overall by a huge amt? Well, if he was smart enough to found NIKE maybe that is the physics lesson we should be applying here, before we write off a couple cc’s of water as insignificant. Great movie too. I followed Pre’s career and I remember where I was when I read about his death. That sucked. But look at NIKE.”


Mark-

A few years before he died in late December 1999, Bill Bowerman and I had a number of long conversations about the design and construction of handcrafted footwear, and specifically custom, high performance running shoes.

Bill was arguably the greatest track coach who ever lived… and among other notable things, he was a maverick hands-on inventor. Interestingly he was very critical of what the corporate sports footwear industry had become… from the early days of no b.s. personally designed and constructed high quality footwear, to modern non-custom overseas mass-production and proprietary raw materials, with an emphasis on cosmetics over function, misleading/ false advertising, etc.

As he shared story after story, it was easy to see parallels to the development of mainstream surfing equipment.

One of Bill’s favorite memories was about the frustrating search for small quantities of the right (exotic) materials, and then personally creating custom one-off running shoes for his elite athletes… ultralight (winning) footwear that sometimes only weighed 4 ounces… a pair!

I’ve often thought if Bill Bowerman’s life had taken a different course, he would have been a truly great designer/ shaper.

Good stuff all…

Here’s another take on the subject highlighting the overall biological component in trying to understand the hydrodynamic influence of porpoise dorsal and pectoral fins. I think it shows there’s more going on hydrodynamically with the biological nature of the study source than just the shape and placement of these fins.

I really like this stuff and those studies even though old are still good reading…

http://www.spawar.navy.mil/sti/publications/reprints/marinemammals/ieee-m-b-9-93.pdf

lunch. out

Dale,

Thanks for the personal anectdote. You made my day.

And I totally agree. Best track coach all time. Hands down.

It’s often over used these days, but in his case it’s true, his genius was pure and original.

I started following Pre’s career in the tiny whos who in sports section at the very bottom of the last page of SI when he was a HS 3 miler. I was in 8th or 9th grade. In the thumbnail picture he didn’t look like a hs track anything. Let alone top hs middle distance runner in the US ever. But there he was in SI! He caught on fast from there. What a tragedy.

Mr. Bowerman’s business experience sounds like what surfing is going through now from the remarks on Sways about out sourcing labor etc. But the reality is surf gear and clothing has been coming out of Asia for a very long time.

You are very fortunate to have had contact. Thanks for sharing.

Mark

Oneula,

I was aware of the Dolphin Skin theory in the early sixties, and considered putting a soft skin on a regular surfboard bottom. However at that time I could not find a suitable material, and let the idea slide. Today there seems to be several choices readily available. A hard low rail design would lend itself to such a project. What with the spray adhesives available, it might be fairly easy to explore.

There is a common misperception that the lift generated by a foil (wing or fin) moving through a fluid medium (air or water) is due to pressure differences (a la the Bernoulli Effect). Nothing could be further from the truth!

As a foil moves through the respective medium, it deflects that medium and, in accordance with the Laws of Newtonian physics (in particular the third Law, ‘for every action there is an equal and opposite reaction’), lift is generated.

A thicker fin deflects more water than a thin fin and that is why it provides more lift.

Check out http://www.aa.washington.edu/faculty/eberhardt/lift.htm

It’s actually a future project I’m considering(sketched out in my head) once I get all my wood lam boards I want done…

I was thinking about shaping a regular board thicker than normal, the routering out the entire bottom 1/2"-1" deep up to the bottom edge of the inside rail line bevel. Then glassing and finishing the whole thing up before inserting and gluing on a panel of soft closed cell yoga mat foam into the routed out bottom. You’d slice and glue the closed cell to slide over the fins glassed on to the board.

The end result would be a hard stiff deck and rails but a bottom panel that would be soft enough to let the water pressure manipulate it to find its most efficient flow as it travels across the material. Need to find some real soft closed cell to do this though almost spongy in nature… I’m sure there’s stuff out their.

Another idea would be to glue some type if finely ribbed latex? airbag to fit in the carved out bottom to work like Dale’s Air mattresses, you just wouldn’t get the overall flex effect though but one hell of a shock absorbing bottom layer. Probably need the world’s biggest ribbed condom to pull it off… Now that would be a lot of fun.

Thinking about it now it seems that maybe an I-beam structure of 3-4" thick floaty foam and solid wood rails surrounding a 1-2" thin aluminum honeycomb corex/aircore body covered in divinycel with a shallow concave deck and a bored out bottom filled with either soft closed cell foam or a ribbed air bag would be the experiment to launch…torsionally still longitudinally semi soft with a very soft and pliable bottom layer to deflect the water pressure. only dreams I guess for now.

Studied this porpoise skin hydrodynamics stuff pretty seriously back in '74-'75 at UW but never built anything though… I probably should’ve gone to woods hole or scripps instead…

“Since electricity comes from electrons, does that mean morality comes from morons?”

LOL!!! Man thats going to be a hit at parties!

a good consolidation of the B vs N debate…

http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html

and a personal info goldmine…

http://www.onemetre.net/Technicl/Technicl.htm

With all the talk about “AOA’s,” and it seems mostly related to “turning” and much less about “trimming,” what do people think about the function of the fin(s) when trimming/going down the line? My understanding is, one of the fin(s) main functions is to keep the board “up” in the wave, so as not to side slip - kind of like the keel in the sail boat vis-a-vis sailing up wind.

how often do you need ALL of your speed unless your some crazy arieal artist orm riding near close outs i feel that boards are rarely pushed to their max speed think of how often you can do a cut back just to burn speed and still once again speed up for another, assuming the waves is long enough. and after reading this i went in my garage and made from scaps of foam two idsentical fins for my bonzer i hope to glass this weekend. can’t up load em sorry

I’ve always thought that a single fin is more like the sail than like the keel. That’s why, trimming down the line, you can go faster than the wave itself approaches shore. Just like sailboats go faster not with the wind dead astern but with it quartering behind. Their keel stops (to an extent) sideslip and the sail uses the wind for power and, with that power, provides thrust. A single surfboard fin, in trim, is doing both.

And single fins go fastest when trimming, turn to burn off speed. Other fin setups, at least if there’s toe-in invloved, slow down when trimming, but accelerate by turning. Totally 180* different thing.

I suppose this thread should clarify whether its talking about fins/fin setups that go fastest in trim or those that drag in trim and go fastest with changing AOA’s.

“Good one?” - The mouse will die. Perhaps an insect is “under the radar” of gravity, but not the mouse. Taylor

It’s interesting, it has been pointed out that most/often 2+ fin boards need to be “pumped” to maximize their ability to generate speed, but how often does one really only do one or the other. I had a bit of this type of discussion with an expert in this field, and we both pondered why there isn’t more emphasis on moving fin’s around a bit, both to see what’s doin’ in certain conditions, and to maximize the boards potential for various conditions. It seems this discussion, while it started about thick v. thin, is often moving towards “the best fin,” when it seems there is no “best” fin, but probably just a best fin for a given board/rider/waves - and that discussion has many, many variables.

My Original question posed to Daddio who made a rather strange comment: “Remember basic physics: Drop a mouse a bee a feather and a boulder in a perfect vacuum and which will fall faster?”

TaylorO’s reply to what I don’t know: It’s a non-sequitur at best. “Good one?” - The mouse will die. Perhaps an insect is “under the radar” of gravity, but not the mouse. Taylor

What that heck does that mean?

Is this some kind of joke?

No wait don’t even bother.

Here.

  1. In a vacuum there is no air. Sure a mouse and any living thing will die. So? In a vacuum without wind resistance they will all fall at the same rate dead or alive.

  2. There is no such thing as escaping the effects of gravity. I’m not even going to ask where that idea came from. It’s wrong.

  3. Everyone else got it. As we know by the silence, which is as it should be.

Come on. This is simple stuff. If someone skipped out on their HS Physics class they should keep that secret to themselves.

Not blab it all over here.

Sorry TaylorO, I lost my patience for a second. I apololgize. It’s not your fault. It’s our education systems fault.

TaylorO,

There is good stuff here.

There have been several excellent posts along the way, where the informaton you are seeking has been broken out in ways that make sense, by guys with great amounts and years of experience and tons of knowledge. It’s worth a look back on previous pages of this thread. Take your time. It’s well worth it.

That is pretty much it for now on this topic. Guys have dropped what they were doing all week, and stopped by and said what they have to say, have said it the way they know it, and learned it, and where they learned it. There is a lot of respect here, too. Feel it. Everyone could feel it as he thread developed. It was pretty cool. Now some guys are going back to try things different ideas based on what they heard here. Some may try thick fins for the first time. Some may question their standard thin fins and wonder, is there another way? Some will be reading links for a while and bookmarking them so they can refer back later. That is the way it is done.

As for guys testing different fin locations, that is done all the time. A lot of it all the time. But it’s usually small incremental changes and tends to coincide with model changes, because the previous years testing goes into it. Shapers have teams, keep files, and take notes on rider feedback. Most shapers have different fin positions for their summer line and their winter line of boards. And they are constantly updating from season to season and annually over the years. Look for small changes from the elite. Look to other threads to find out why some people think that is and form your own conclusions. Find a shaper you like and get to know him and talk with him and order boards from him.

Get involved. Keep an open mind so you will be ready to be stoked. Treat people like people. That’s all it takes.

Thanks for dropping by. It was a good week. Hope you enjoyed it as much as I did. Mark

Wha…tha…? Surface area - volume - weight? dis - place - mint??? Damn that water is hard. “Hey Culligan Man.”

There is much separation between theory and practice.

You’ll note that I didn’t say - mouse with a man made lead parachute.

My best friend just retired from the Ventura County Fire Department, and had told me that when they would go to a high rise structure fire, the mice would dive out of a broken window, hit the ground and do a little dance, then scamper away - freaked him out the first time he saw it!

I sat in the back of most classes and designed things in a sketch book thru most of High School, but found this article in a magazine in an art class in Junior College - Natural History Magazine - '74. This article has rattled around inside my head for most of 30 years, and aside from my maybe not saying it just exactly right from a science viewpoint, it did silence everybody long enough for the questions to start popping up and I’m sure everybody was trying to picture the macro/micro thing that I was talking about. Lord knows it’s hard for me to type these posts out and I always get NAILED for the little piddly things like doobies and buddha and mice and sureforms, but I dare you to honestly answer any of these posts from your heart as well as your mind and not be affected. I’ve always looked forward to TaylorO’s replies. And I try just that much harder to challenge him as much as he challenges me - the next time. Silence is for fools. Have a nice day.

Retyped here without permission:

Natural History, January 1974

Size and Shape

The immutable laws of design set limits on all organisms.

Steven Jay Gould

Museum of Comparative Zoology, Harvard University

Who could believe an ant in theory?

A giraffe in blueprint?

Ten thousand doctors of what’s possible

Could reason half the jungle out of being.

POET John Ciardi’s lines reflect a belief that the exuberant diversity of life will forever frustrate man’s arrogant claims to omniscience. Yet, however much we celebrate diversity and revel in the peculiarities of animals, we must also acknowledge a striking “lawfulness” in the basic design of organisms. This regularity is most strongly evident in the correlation of size and shape.

Animals are physical objects. They are shaped to their advantage by natural selection. Consequently, they must assume forms best adapted to their size. The relative strength of such forces as gravity varies with size in a regular way, and animals respond by systematically altering their shapes.

The geometry of space itself is the major reason for correlations between size and shape. Simply by growing larger, an object that keeps the same shape will suffer a continual decrease in relative surface area. The decrease occurs because volume increases as the cube of length (length x length x length), while surface increases only as the square (length x length): in other words, volume grows more rapidly than surface.

Why is this important to animals? Many functions that depend upon surface must serve the entire volume of the body. Digested food passes to the body through surfaces; oxygen is absorbed through surfaces in respiration; the strength of a leg bone depends upon the area of its cross section, but the legs must hold up a body increasing in weight by the cube of its length. Galileo first recognized this principle in his “Discorsi” of 1638, the masterpiece he wrote while under house arrest by the Inquisition. He argued that the bone of a large animal must thicken disproportionately to provide the same relative strength as the slender bone of a small creature.

One solution to decreasing surface has been particularly important in the progressive evolution of large and complex organisms: the development of internal organs. The lung is, essentially, a richly convoluted bag of surface area for the exchange of gases; the circulatory system distributes material to an internal space that cannot be reached by direct diffusion from the external surface of large organisms; the villi of our small intestine increase the surface area available for absorption of food (small mammals neither have nor need them).

Some simpler animals have never evolved internal organs; if they become large, they must alter their entire shape in ways so drastic that plasticity for further evolutionary change is sacrificed to extreme specialization. Thus, a tapeworm may be 20 feet long, but its thickness cannot exceed a fraction of an inch because food and oxygen must penetrate directly from the external surface to all parts of the body.

We are prisoners of the perceptions of our size, and rarely recognize how different the world must appear to small animals.

Other animals are constrained to remain small. Insects breathe through invaginations of the external surface. Since these invaginations must be more numerous and convoluted in larger bodies, they impose a size limit upon insect design: at the size of even a small mammal, an insect would be “all invagination” and have no room for internal parts.

We are prisoners of the perceptions of our size, and rarely recognize how different the world must appear to small animals. Since our relative surface area is so small at our large size, we are ruled by gravitational forces acting upon our weight. But gravity is negligible to very small animals with high surface to volume ratios; they live in a world dominated by surface forces and judge the pleasures and dangers of their surroundings in ways foreign to our experience.

An insect performs no miracle in walking up a wall or upon the surface of a pond; the small gravitational force pulling it down or under is easily counteracted by surface adhesion. Throw an insect off the roof and it floats gently down as frictional forces acting upon its surface overcome the weak influence of gravity.

The relative weakness of gravitational forces also permits a mode of growth that large animals could not maintain. Insects have an external skeleton and can only grow by discarding it and secreting a new one to accommodate the enlarged body. For a period between shedding and regrowth, the body must remain soft. A large mammal without any supporting structures would collapse to a formless mass under the influence of gravitational forces; a small insect can maintain its cohesion (related lobsters and crabs can grow much larger because they pass their “soft” stage in the nearly weightless buoyancy of water). We have here another reason for the small size of insects.

The creators of horror and science-fiction movies seem to have no inkling of the relationship between size and shape.

The creators of horror and science-fiction movies seem to have no inkling of the relationship between size and shape. These “expanders of the possible” cannot break free from the prejudices of their perceptions. The small people of Dr. Cyclops ,The Bride of Frankenstein ,The Incredible Shrinking Man , and Fantastic Voyage behave just like their counterparts of normal dimensions. They fall off cliffs or down stairs with resounding thuds; wield weapons and swim with olympic agility. The large insects of films too numerous to name continue to walk up walls or fly even at dinosaurian dimensions.

When the kindly entomologist of Them discovered that the giant queen ants had left for their nuptial flight, he quickly calculated this simple ratio: a normal ant is a fraction of an inch long and can fly hundreds of feet; these ants are many feet long and must be able to fly as much as 1,000 miles. Why, they could be as far away as Los Angeles! (Where, indeed, they were, lurking in the sewers.) But the ability to fly depends upon the surface area of the wings, while the weight that must be borne aloft increases as the cube of length. We may be sure that even if the giant ants had somehow circumvented the problems of breathing and growth by molting, their chances of getting off the ground would have been far worse than that of the proverbial snowball in hell.

Other essential features of organisms change even more rapidly with increasing size than the ratio of surface to volume. Kinetic energy, for example, increases as length raised to the fifth power. If a child half your height falls unsupported to the ground, its head will hit with not half, but only 1/32 the energy of yours in a similar fall. A child is protected more by its size than by a “soft” head. In return, we are protected from the physical force of its tantrums, for the child can strike with, not half, but only 1/32 of the energy we can muster. I have long had a special sympathy for the poor dwarfs who suffer under the whip of cruel Dr. Alberich in Wagner’s “Das Rheingold.” At their diminutive size, they haven’t a chance of extracting, with mining picks, the precious minerals that Alberich demands, despite the industrious and incessant leitmotif of their futile attempt.

This simple principle of differential scaling with increasing size may well be the most important determinant of organic shape. J.B.S. Haldane once wrote that “comparative anatomy is largely the story of the struggle to increase surface in proportion to volume.” Yet its generality extends beyond life, for the geometry of space constrains ships, buildings, and machines, as well as animals.

Medieval churches present a good testing ground for the effects of size and shape, for they were built in an enormous range of sizes before the invention of steel girders, internal lighting, and air conditioning permitted modern architects to challenge the laws of size. The tiny, twelfth-century parish church of Little Tey, Essex, England, is a broad, simple rectangular building with a semicircular apse. Light reaches the interior through windows in the outer walls. If we were to build a cathedral simply by enlarging this design, then the periphery of the outer walls and windows would increase as length, while the area that light must reach would increase as length times length. In other words, the size of the windows would increase far more slowly than the area that requires illumination. Candles have limitations; the inside of such a cathedral would have been darker than the deed of Judas. Medieval churches, like tapeworms, lack internal systems and must alter their shape to produce more external surface as they are made larger.

The large cathedral of Norwich, as it appeared in the twelfth century, had a much narrower rectangular nave; chapels have been added to the apse and a transept runs perpendicular to the main axis. All these “adaptations” increase the ratio of external wall and window to internal area. It is often stated that transepts were added to produce the form of a Latin cross. Theological motives may have dictated the position of such “outpouchings,” but the laws of size required their presence. Very few small churches have transepts.

I have plotted periphery versus the square root of area for floor plans of all postconquest Romanesque churches depicted in Clapham’s monograph of English ecclesiastical architecture. As we would predict, periphery increases more rapidly than the square root of area. Medieval architects had their rules of thumb, but they had, so far as we know, no explicit knowledge of the laws of size.

Like large churches, large organisms have very few options open to them. Above a certain size, large terrestrial organisms look basically alike—they have thick legs and relatively short, stout bodies. Large Romanesque churches are all relatively long and have abundant outpouchings. The invention of the flying buttress strengthened later Gothic buildings and freed more wall space for windows. Churches could then become relatively wider and simpler in outline (as in the Cathedral of Bourges).

The “invention” of internal organs helped animals retain the highly successful shape of a simple exterior enclosing a large internal volume; and the invention of internal lighting and structural steel has helped modern architects design large buildings with simple exteriors. The limits are expanded, but the laws still operate. No large Gothic church is higher than it is long, no large animal has a sagging middle like a dachshund.

I once overheard a children’s conversation in a New York playground. Two young girls were discussing the size of dogs. One asked: “Can a dog be as large as an elephant?” Her friend responded: “No, if it were as big as an elephant, it would look like an elephant.” I wonder if she realized how truly she spoke.

Biology doesn’t make very much sense without physics. Mike

Dddio,

I’m a big fan of the hammered truss myself:-)

I sat all over the place in HS. We didnt have any hot chicks in our classes so that was not a factor. In college I tried to get the backrow. If there was anything they didnt allow I was on it. I took up smoking because they didnt allow it. Boy was I stupid. Fortunatley that habit bit the dust a long time ago. But seminars were so small we just sat around a small table. Nowhere to hide so I had to do my homework readings on time and get involved in the discussions. That was tough, because I took my Senior Seminar my sophmore year. Scheduling conflict. I pulled it off. Sartre Seminar. It left me seriously and permenantly deranged:-) Scarred for life.

Twenty years later I went back for a visit. First thing I wanted to see was if my typewriter ribbon was still draped in the tree outside my dorm where I threw it that fateful winter? It wasn’t. Bummer. But I was strutting around campus with my 30 yr trophy GF so I was the badass.

That reminds me of a Jack Nicholson anectdote. This happened two years ago. Many of my team riders either go to or went to school at Manasquan HS, NJ. Jack is an alumni. One winter morning one of my team riders had been surfing and got to school late. He let himself in and closed the door behind him. As he walked down the hall he heard someone knocking on the door, so he went back to let the person in. It was Jack in long dark coat and shades with his hot 19 yr old GF behind him.

Jack introduced himself and thanked him, then proceeded to walk down the hall. When suddenly he stopped and turned to face my team guy and said, no try and hear Jack’s drawn out voice here because its perfect…“Youuu knowww. YOUuu look, the way I feellll, RIGHT NOwwwwWWW?”

True story.

Very interesting read. I would have liked to have heard the conversations of the cathedral designers stating why they needed to build the way they did without engineering school or BOCA or structural analysis or anything but guts and glory. Kinda like where we are now with fins.

I have a little pet theory of my own that goes like this: Earth, at any given time, supports exactly as much life as it possibly can. Extrapolate that this way: Our galaxy is the blueprint for life. To wit if one were to look for life as we know it in other parts of the universe things to look for would include, first our size sun. Next our size planet with our size moon. All these things are necessary to keep the right gravity and tension and distance from sun to keep water in liquid form which is absolutely necessary to support life as we know it. Next look for the color blue.

But first thing I noticed on your article was a familiar source.

Museum of Comparative Zoology, Harvard University.

That is where I sent MVGs to Jennifer C. Nauen back in 1999.

She was another ally. I found a link to her paper on tuna finlets.

http://www.biolbull.org/cgi/content/full/200/1/9

MY brother informed me that my contribution to her research was the idea of contributing flow to the tail fin vortex.

She wrote:

“Such future experiments with flow visualization will reveal whether the finlets alter the path of water flow in their vicinity and whether that water is directed into the tail vortex, potentially increasing swimming efficiency.”

It wound up in the last line of her conclusion because I didn’t talk with her till after her research was done and they were mostly done writing this paper.

Check it out. Then, imagine if we had that kind of research on surfboard fins, instead of the thick vs thin article. Mark

You might try checking out the California eigth grade science curriculum. Its been in there for years!

DanB said: “You might try checking out the California eigth grade science curriculum. Its been in there for years!”

Dear Mr. DanB;

I have no idea what you are talking about. With almost 100 replies on this thread you are going to have to be a little more specific as to exactly what “its” refers back to. Please, if you will, take the time to cut and paste the phrase, and a little of the surrounding context you are addressing, as I have done for you. It’s a courtesy.

I have steadfastly maintained that it’s important to keep this discussion on a simple level, because that is where I contend any kind of conclusion about fins should fall. Most posts on this thread have begun with personal conclusions and then sometimes worked back when called upon to support claims, so, hopefully, you see my point. That point being it has to be understandable by a 14 yr. old or it’s almost worthless. That has been my point all along. Right now I don’t know any 8th. graders. The most recent crop of 8th graders I had on my team are now Seniors. I guess it’s time to recruit some more. But I would rather hammer red hot nails in my eyes, than put myself through that process again.

By the way the correct spelling for “eigth” is “eighth”. Although “8th.” is acceptable to me here, I would not use it in work I planned on turning in to an 8th. grade teacher. Also, there is a spell check button below. It’s there for a reason. You might familiarize yourself with it’s use. It helps. I use it most of the time. When I don’t is shows. Also, the proper contraction for “it has” is “it’s”.