Fins of the ocean

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If you go ride D fin longboards and then try a dolphin fin, it is a HUGE step forward.

I wonder why the hammerhead shark uses a D fin then ?

:slight_smile:

http://www.isidore-of-seville.com/hammerhead/3-2.html

scratching my head wondering how this could end with discussion of the D fin which clearly doesn’t grow on a hammerhead of that matter appear on any sea beast that swims with significant speed or maneuverability.

Good nite, Rich

Hi Rich,

You might try looking at this picture, which was taken by Blakestah and posted at the top of this thread for discussion:

Looks like a D Fin to me

"

So do these ones:

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Hi Rich,

You might try looking at this picture, which was taken by Blakestah and posted at the top of this thread for discussion:

Looks like a D Fin to me

"

So do these ones:

a D fin has its tip closer to the middle, not on the rear edge - it looks like the letter “D”

From the fin shop:

When I comes to “D” fin on surfboards we are dealing with definition. The photo that Blakestah shares of a vintage longboard with it’s red fin is one version of the “D” fin as I know them. The are others that are configured a little differently but they all have that same straight line at various rake angles as their leading edge. The photo that Bloke shares is just one of the many Hammerheads that swimm the sea. The bonnethead is certainly a beautiful example of hydrodynamic effeciency. For my part the lines and fin shapes of Sphyrna Mokarran (attachment) are the ones that transpose (with a measure of my own self appointed artistic license) best into functionality on a surfboard.

Growing from the matrix of the great pelagic travelers I find integral lines set in precise complex arcs and distinct angles that facilitate the type aquatic performance that enables each creature to make its living in a separate way. I dream about these lines and sketch them as I attempt to create evolving surfboard fin shapes.

Observation: Some of we land based creatures seem possessed by demonstrating the distance one can make excrement travel before it hits the ground, or find speading it over some else’s words entertaining; either excercize seems to be IMHO very unthrifty. In the sea there is a completely different paradigm as the stuff goes instantly into the wash.

For my part it’s not about being right, but rather sharing visions. Someone may be the best today but fame is soon gone. Sammy Davis was one of the finest dancers who ever lived but few remember him. What kind of fools are we?

Happy Easter, Rich

Good post Blakestah. I cant stop thinking about fins in the natural world lately, Went to the british natural history meuseum this week and spent ages in ‘the blue whale room’ checking out all the different fins on the cetacea. Inspiring stuff which already has the brain ticking with new ideas for the next board. Noticed that alot of the pelvic fins resembled those seen on the new van straalen boards.

Stick your hand out a car window some time and use your fingers as wing flaps. Imagine your hand inside a rubbery fin. This photo is of the bones in a whale flipper…

Hi Blakestah, thankyou for that information, I was under the impression that d fins looked like this:

Checked swaylopedia but there’s no entry for D fins.

What I was commenting on was this statement of yours:

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If you go ride D fin longboards and then try a dolphin fin, it is a HUGE step forward.

What I thought you meant by “dolphin fin” was a fin with a trailing edge that is raked aft like this:

As compared with the hammerhead fin which you posted, which has more of a vertical trailing edge, and which doesn’t resemble a dolphin fin . . . . seems to work for the hammerhead shark and it’s also similar to some popular longboard fins.

About aspect ratio: you say that the fins posted all have an aspect ratio of around 1:1, but this is only true if you take the height of the fin and the overall fore and aft length which the fin spans, this seems misleading as a very narrow raked fin then winds up with a low aspect ratio according to you when in reality it is a high aspect ratio fin. An example is the right whale fin which you posted, it has an aspect ratio closer to 5:2. Do you see what I mean ?

Cheers

Roy

Hi Roy -

I just added “D Fin” to Swaylopedia. I took the liberty of including pics posted here by yourself and Blakestah. Please feel free to add anything you feel I missed.

http://www.swaylocks.com/…edia/index.cgi?D_Fin

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Stick your hand out a car window some time and use your fingers as wing flaps. Imagine your hand inside a rubbery fin. This photo is of the bones in a whale flipper…

OMG, it’s got no thumb!!!

NIce post blakestah…

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And speaking of BS, I have never ragged on your posts regardless of how useless I found them…….

You’re a better man than me.

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AC: Glad you liked the Monterey Aquarium, hope you got to see the great white…..

They let the shark go about a month ago. My girlfriend and I happened to be down in Monterey with a half-hour to kill. We popped into the aquarium (we’re members so we don’t have to buy tickets to get in) to see the young male great white (their second white shark - the first female was released last year). The male had a really different presence than the female. Much more ominous. The next day, they released him back to the sea. We felt very lucky to see him first.

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You’re looking at the pectoral fins, which act more as stablizers than a rudder. Not that I don’t think the shape is relavant, but those aren’t the shark’s primary fins for quick direction changes.

You can think of an airplane as a rudementary copy of a fish. One major difference is the overall plane isn’t dynamic… just some of its individual parts. Those parts relate directly to fish fins - ailerons, flaps, elevator, rudder. Airplanes and fish use these control surfaces to change direction in a 3D environment. Surfboards are only changing direction on the surface of the water and don’t need the complexity of a fish to work well.

Another point is… surfers are tapping into a wave’s energy, and don’t require anything other than getting pushed fast enough with sufficiant control to have a good time. Fish and airplane performance is more of a life or death thing. Both must also be capable of generating their own energy and speed.

Kendall,

The Bonnethead in the photo from my perspective appears to be to be a highly evolved glider. The contours of his head and pectorals embrace that kind of locomotion. With the wide surfaces we see on him abupt directional change or quick elevational adjustment will be a bit of a struggle. Long base cord projecting from the body matrix does not release from it’s established direction well. (Traditonal Keel fin Fish boards)

Howerver his bigger cousin the great hammerhead shark – Sphyrna Mokarran has much more pointed fins, carries them much differently and has a head of a far different profile. He is one of the most agile of swimmers in the sea even though he’s a very big fellow.

In this link (http://www.sharkattackfile.net/species.htm)

shows some very good shots of several different shark species. Certainly sharks are not the only ones we can take ideas from for fin profiles but these photos will lend themselves nicely to thought on the subject.

We all come to this forum with our own opinions. Mine are different than yours so I’ll share them here.

Where I disagree with you Kendall is when you say, “Surfboards are only changing direction on the surface of the water and don’t need the complexity of a fish to work well.” If one looks at the contours of surfboards built in the 70’s and compares them to those of today one finds that those of today entertain many more complex arcs in tangent to those of yesteryear. Thus they are more in immitation of the multidimensional contours of aquatic animals and as result the boards of today perform better. This is not to say that there weren’t some grand shapes in the 70’s or that some of the ideas from that era are not seen in the creations of today. Any good shaper will tell you that he is marrying the old with the new and getting something better all the time.

Kendall, when I read your text I sense that you are very unexicted about how evolved aquatic shapes apply to surfboards. I on the other hand am initiated by them and also by those of birds. For I see surboards are a marriage of things aquatic and things avian. Surfers move much like birds banking on the wind. The also have purchase under them that affects their ability to accelerate and maneuver.

It is my feeling that we surfers don’t operate and 3 demensional world but in all of the eleven demensions that modern physics entertains. When we see how water moves we begin to sense how we must make out boards more like membranes and less like dinner plates.

Back to work, Rich

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When we see how water moves we begin to sense how we must make out boards more like membranes and less like dinner plates.

Holy airbag, Batman! That sounds like one of Dales Neumatic surf craft to me!!!

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Kendall, when I read your text I sense that you are very unexicted about how evolved aquatic shapes apply to surfboards. I on the other hand am initiated by them and also by those of birds. For I see surboards are a marriage of things aquatic and things avian. Surfers move much like birds banking on the wind. The also have purchase under them that affects their ability to accelerate and maneuver.

Hi Rich,

No… actually I agree with you that the shapes apply. I just don’t agree with some of the posts about how they apply. I oversimplified my feelings just to make a point. The thing that made me respond was comparing a pectoral fin of a gliding shark (used for stability) to that of a surfboard fin that’s made to help control turns.

I know surfing has more than two dimensions. My main point there is we are dependant on an external force to give us momentum, wereas fish have to generate it from within. Therefore in my mind fish are required to be more complex. Not that surfboards can’t be… just that they don’t have to. Also… I surf for fun. Having fun isn’t always directly related to how effectively the board travels through the water (for me). Sometimes a slow cumbersome supertanker is the ticket. Other times I want something zippy and quick. On rare winter days I want something that is just plain fast down the line and easy to paddle into monster death drops. Mostly I’m just looking for a board that will give me the most pleasure in the specific conditions of the day. I don’t have to be the fastest surfer on earth. I just have to be able to surf faster than the wave I’m on.

As with fish (or any animal) there isn’t one design that does it all. I show up at the beach with a few boards and use the one that feels right for the conditions of the day.

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Another point is… surfers are tapping into a wave’s energy, and don’t require anything other than getting pushed fast enough with sufficiant control to have a good time.

Kendall,

As you should know by now surfers are dependent (for waveriding motion) upon the force of gravitational attraction between objects, and do not generally get ‘pushed’ .

I notice that this comment of yours (That surfers just get pushed etc) contradicts your other posts in which you state the importance of pumping the board for speed. . . . pumping the board for speed is very similar to what fish do to drive themselves !

Also, you say that fins are only for steering the board. Now notice this: The side fins on the shark (which are not used for primary propulsion) are according to you, not as relevant as the tail fin . . … . and yet by your own ‘analysis’ the surfboard fin is a static steering device, and thus more similar to the shark side fin !

Your posts specialise in sounding intelligent, but they are so full of contradictions that they are very time consuming to unravel.

This thread was intended ( by Blakestah ) to be a discussion of surfboard aspect ratio and rake in comparison with the fins of marine animals. . . so far I am the only one to comment on either of those topics !

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Roy… I don’t recall ever saying surfers were “pushed” by a wave. I said we tap into the waves energy. My point is simply that as surfers we depend on a wave to do more than paddle or bob. Fish generate their own momentum, with or without waves.

I’m not discounting the effects of aspect ratio or rake in a fin’s performance. I’m also not saying we can’t learn from the designs of fish… in fact I believe that’s where most of our inspiration should come from. There is just more to surfing than fin shape.

OK… you can go back to hyping your unique and expert knowledge of all things in the universe ; )

Maybe I am crazy but I have always thought that sharks sort of have a flexible bit of tissue on the trailing edge of their dorsal fin (dark gray region of attachment) making their fins sort of a cross between a D fin and dolphins fin.