Shark skin coating

Discussion in 'Materials' started by Luis Cunha, Oct 24, 2007.

  1. Luis Cunha
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    Luis Cunha Junior Member

    Shark skin is made of a matrix of tiny, hard, tooth-like structures called dermal denticles or placoid scales. These structures are shaped like curved, grooved teeth and make the skin a very tough armor with a texture like sandpaper. They have the same structure as a tooth with an outer layer of enamel, dentine and a central pulp cavity.
    These scales also help the shark swim more quickly because their streamlined shapes helps decrease the friction of the water flowing along the shark's body, by channeling it through grooves.

    Do you know any coating/finishing for boats which has the same proprieties of shark skin?
    Do you think this kind of coating/finishing can improve the boat performance?

    Thanks in advance for you comments.
     
  2. TerryKing
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    TerryKing On The Water SOON

    Shark Skin

    Luis, I saw something about this recently at the China High Tech Show.. I'll have to dig through my pile of literature, but I just had my shipment of household and tools arrive here in China, and it will take a couple of days....
     
  3. Kaptin-Jer
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    Kaptin-Jer Semi-Pro

     
  4. Pericles
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    Pericles Senior Member

    Studies have found that the denticles create tiny vortices that reduce drag to make swimming more efficient. Denticles also allow sharks to swim silently compared to other fish that generate considerable noise when they play the water. http://en.wikipedia.org/wiki/Dermal_denticle

    In Japan, traditional sword-makers used shark-skin for the hand-grips of swords, to make them less likely to slip in the hand.Then the leather is called Shagreen.
    http://en.wikipedia.org/wiki/Shagreen

    On that basis, a silicone rubber cast could be taken from a shark and then used to print the pattern into thickened epoxy resin on the bottom of a boat. It probably would take some experimental work and if it did work, the boat would not reverse too well. :D :D :D

    Give it a go.

    Pericles
     
  5. Bergalia
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    Bergalia Senior Member

    I've a vague idea that the Australian Olympic swimming team experimented with a material (not unlike shagreen) for their 'cozzies' back in 2000. Maybe a similar material would be available (at a price) for your purpose.

    ** Yes, just looked it up:
    The Speedo 'Fastskin' suit was most controversial design, produced specifically for competitors in the Sydney 2000 Olympic Games.

    Fastskin can be considered Speedo's most sophisticated and technologically advanced solution to aiding competitors speed through water.The suit was developed and trialled over several years by a team that included scientists, a biomechanist, a shark expert, a computer clothing company, a Japanese textile company, a swimming coach and swimmers.

    The core research team discovered that the sharks unique skin structure minimised drag and helped make it move faster through water. From this idea Speedo developed a similar skin for swimmers using a specially developed knitted fabric with a tooth shaped surface print.

    The Fastskin launched at the Olympic site, Homebush Bay in Sydney, Australia in April 2000. Controversy arose when it was claimed the swimsuit gave the wearer a technical advantage over other competitors and there were calls to ban its use in the Olympic Games. However in the context of the evolution of competitive swimwear, design and technological innovations have always been devised to enhance the swimmers performance, the Fastskin is just part of this development.

    Made from a knitted super-stretch nylon/elastane/polyester fabric the Fastskin features V shapes ridges and a denticle surface print. In water the effect of these surfaces combine, with large vortices formed by the fabric print flowing in the opposite direction to the small vortices formed in the fabric ridges. This ensures the water is sucked closer to the body which reduces friction drag on the swimmer by allowing surrounding water to pass over more effectively.
     
  6. Pericles
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    Pericles Senior Member

    Bergalia,

    Now you've reminded me, I recall the brouhahaha:D :D :D :D :D :D :D

    Now I'm covered with chagrin.

    Pericles
     
  7. mastcolin
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    mastcolin Senior Member

    Yes they work. Yes they have existed (I think coating was applied as a film as opposed to a wet paint). Aircraft also experiment with these. Boeing basically wallpapered a plane...or was it Airbus, as trial.

    They are illegal in yacht racing under any class rules. They were banned in late 80's.

    Wet sand the bottom of your boat like everyone else does:)

    ps The RORC did research years ago. There are papers/articles out there.
     
  8. Petros
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    Petros Senior Member

    If I recall this properly there is only an advantage in certain Reynolds number ranges, and if this skin produces tiny vortexes, I imagine it only reduces drag for certain shapes at fairly narrow speed ranges. Vortexes "cost" in drag when you generate them, the question is if the "cost" of the tiny vortexes is less than the improvement in flow you are trying to affect down stream of the vortex generators. A shark uses body undulations to propel itself, in a similar way to a swimmer, and since a shark (or a swimmer's) flow is always transitioning, there may be advantages for a vortex generating skin in those speed ranges. I can not see how that would be useful in all operation conditions, on all vessels of all sizes or speeds.

    Better understand why it works and under what conditions before you go to the trouble to apply it to what ever you are building. I understand most custom sail boat makers have a certain grit of sand paper they use on the bottom and rudders to achieve a similar effect.
     
  9. RSALVAREZ
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    RSALVAREZ Junior Member

    Hi To Every One, I Remember The Airplane Test, Was An Airbus And Show A Reduction On Fuel Consumption, They Scan The Skin Then Build A Mold, Then A Complete Skin For The Plane And Reduce The Drag , May Be Is Like The Torpedo From The Kursk??, The Hydrifoil Aplied To The Hull Is An Example Of This , Can You Imagine Millions Of Hidrofoils To Create A Forward Trhust And Reduce Drag?? I Do
     
  10. Pericles
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    Pericles Senior Member

    Petros,

    The eternal question about the bottom of a boat. Matt or shiny? I reckon the test is to finish port and starboard sides with the two choices and see if the vessel moves or veers one way or the other, when given a straight push? :D :D :D :D :D

    Pericles
     
  11. Petros
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    Petros Senior Member

    Pericles,

    That would work better on a catamaran, the wider the stance the better. On mono-hulls it would be very difficult to know since they are seldom perfectly symmetrical as it is. The classic test, two models towed with a balance beam connecting them.

    It occurred to me while finishing my last sailboat (a 14' sloop day sailor) that symmetry was not important since when underway a sail boat hull is never symmetrical in the water anyway. Yet all of the books and plans make such a big issue out being fanatical about symmetry in the hull. In a sail boat it is not relevant within minor limits, power and paddle boats yes, sail boats NOT!
     
  12. wannasail53
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    wannasail53 Junior Member

    Probably too late as old post but:I have thought about this for many years after reading that the old golf balls where slick rather than dimpled and the dimpled ones go much farther than slick.Since a hull going through water drags water it would seem to me that the small vortexes would decrease the amount of water you are dragging along with you.
     
  13. Pericles
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    Pericles Senior Member

  14. kach22i
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    kach22i Architect

    Anyone know where I can get samples of Fastskin or purchase fabric on a roll?

    I'd like to see if it make a good hovercraft skirt material.
     

  15. Pericles
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    Pericles Senior Member

    I doubt it's tough enough or windproof. Think Speedo.

    Perry
     
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