Lee.V introduced two very important words into this discussion on the ‘Theory of balance’ the other day that I’m not sure has been considered enough. That is; Force(mechanical interaction b/w an object and its surroundings) and Vector(dircetion of force). I’ll throw some more out there - Moment of interia(resistence to rotation), torque (rotatioanl force), velocity(speed x displacement), Momentum (the quantity of motion possed by an object), and angle of incidence( described by the angle at which a foil hits the a fluid and results in a vector force) . Lift(as in a plane wing) is not really best described by Bernoulli’s equation (high-low presure gradient either side of a foil). Newton is the man that should be being discussed more when talking fin design and board design. There is a critical velocity which is exceeded during most surfed waves that causes Benoulli priciple to become less pertenent than Newtonian law. As is the case in 99.9% of plane wings and also race car aerodynamics. Newton’s Surfing Laws 1)LAW OF INERTIA: A surfboard will not move or accelerate unless acted upon by a force(i.e. paddling-catching the wave, and gravity-once riding) 2)LAW OF ACCELERATION: The rate of change of momentum of a surfboard is proportioanl to the force applied and takes place in the direction in which the force acts( i.e down the line speed and profile drag of the board outline and fins) 3)LAW OF ACTION-REACTION: To evey action there is and eqaul and opposite reaction (this allows us to walk on water and a fin to create stability and a change in direction). So back to the magic fin. The total effect of fin design is a combination of all the below statements (in brief). Newton’s laws suggest that- 1) the rake of fin and the side on surface area are most influential in creating change of direction. Both these variables influence the amount torque that is required to rotate the fins through the water thus creating a change in direction of the surfer. So the greater the rake the more resistance to rotation it has. This is also so for surface area. 2)Toe and camber in combination will induce an undesirable drag force when set at anything other than 0 degres to the flow of the water across the fin. We can’t get around that. But the anvantage of these variables is that they allow us to influence the vector forces that occur when set 0 degress. Vetor forces occur perpendicluar to the surface of the fin as water flow across and ramps of it. This ramping effect induce infinate vectors across the suface on the fin that over time(when trying to turn) and will also influnce turnablity of the board. These forces are outway the drag created by about 70%. 3) That leads us to the foil of a fin and front on surface area. The more hyrdodymaic we can make a fin, by varying foil, the less drag that will be created. The more we decrease front on surface area, by changing width and height, the less resistance (not drag) will be created. Drag affects our ability to accelerate -law 2 & 3, and front-on surface area is explained by law 3. Both drag and surface area are trying to slow us down. Again, undesirable. 4)Fin shape. The dynamic nature of water flow across the fin, the composition of the fin and the above previous ideas on toe, camber, torque, drag and all the other many variable this design concept must incoporate, will ultimately bring about the overall shape of the fin. I think cosideration to these aspects first is not really done and fin shape is the first thing considered first. I’m not saying its wrong, I’m just saying it might not be right! The above is just the fin being considered, albeit briefly, but Newton applies to all aspect of surfboard design. What about this idea. Consider that the dolphin fin and varients of it(for example) are widely used on many surboards. Consider also, that here we are ideally trying to get the same thrust ,turn, and stabilty out of 1, 2, or however many fins, all on the same plane(ie on the bottom), that a dolphin gets using using 4 foils all on different planes. Perhaps the surfboard being a non-natural mechanism needs a non-natural fin design approach. Pehaps we need a unique design of fin that is unique to the surfboard. Perhaps we need to copy nature more exactly, with fins on the tail rail for example, or maybe incorporate technology used from the multi million $ race yachts? I’m not sure how or what will be done but we can’t let little problems like this prevent use from creating the next great idea. It hasn’t prevent the Bob McTavish’s and George Greenough’s of this sport fom creating. Good luck! PS: The point I was trying to make was that maybe Newton makes more sense and more accurately describes the physical priciple of surboards design and riding.
Naki: G. Greenough present fin of choice looks nothing like the organic versions of the past so I think your right that we should look more to fins that work not ones that “look” right… The history of surfboard design shares a lot with early boat building; try something and if it works, keep doing it. There wasn’t much science in either until boats stopped using the wind and surfboards started using more than one fin. It’s not that the physics didn’t apply, its that there was no need to really understand the physics to get something to work. I really like Greg Loehr’s and Tom’s pitch control thoughts. I’m sure you could have asked any marine engineer and they would have told you about using resistance as a means of trimming pitch, but no one did. With changes in building materials and the complex relationship with multiple fins and bottom contours, maybe its time for more physics and engineering to play larger roles in design. It will certainly be needed if flex is used in hard, stand-up surfboards. The trial and error approach to flex is terribly time consuming (and therefore expensive). If a mathamatical approach could save time, it might be worth the investment. The next leap in surfboard design, in my opinion, has as good a chance of jumping off someone’s computer screen as out of a garage in Santa Barbara. I hope that everyone out there isn’t afraid of physics and science. It’s just another language. It’s just a little more precise than “flat is fast, curved is slow”. If we don’t start to use these tools, we’ll be stuck riding Spanish Galleons instead of America’s Cup yachts. Newbs
looking to nature is where the whale tail fin idea came from.we have essentially been using a dorsal fin for board fins.(single fin in particular)looking for more drive i got to thinking about dolphins and how they can accelerate so damn fast with a couple flicks of their tails.dorsal fin-vertical and for steering and stability.tail fluke-horizontal for pure power and drive.perhaps it can work on a board even though it has to be placed vertical rather than horizontal, the idea being the foil, template, etc. of the tail will work no matter it’s postioning.PG did all the design building and r&d along with us and the whale Tail fin was put into use.perhaps not a breakthru design but sure works better than anything else in a few of our boards.Always looking to improve…
Matt, Nature is a great source of inspiration but you have to remember that evolution is usually thinking of more things than efficient foiling. If it were, all fish and other aquatic animials would have nearly identical fins. The acceleration you see is mostly due to the muscle power of the animal’s entire body not the shape of the flukes. That said, the transfer of the animal’s motion into forward momentum IS dependent, in some part, to the foil and shape of the fluke. Anyway, at some point, we have to admit that a surfboard is not a cetacean and that there MAY be more efficient fins than the organic shapes of the past. On another note; Mr. Liddle sent me a picture of his ankle x-ray…He’s got more screws and brackets in there than a Home Depot! Ouch…
“On another note; Mr. Liddle sent me a picture of his ankle x-ray…He’s got more screws and brackets in there than a Home Depot! Ouch…” Lee V… I can relate. Two pieces of hardware going through my ankle joint look suspiciously like 1 3/4" drywall screws, and on my fibula there`s a 6" long steel plate with 7 smaller screws. As a reality check, I keep a couple full-size x-rays in my shop. Metal detectors see me coming a mile away.
Uh oh here I go (again).Fins…fish…fins…fish.Fish fins.Someone needs to go outside of the box and look into other designs.We have been tweaking surboard fins for 30 years and they all still look like fish fins.The B1 bomber doesn’t look like it would fly to me but I guess it is O.K…Maybe a good fin (skeg) should look like coke bottle…who knows?..just an opinion…maybe worth two cents or so. R.B.
For fins I like Cheyne Horan’s (& Ben Lexcen’s) Starfin. It resembles a WWII British spitfire more than any fish. Plus it adds a planing surface independent of the surfboard. Not sure how it affects pitch or trim but it rips! I really recommend them. Rob Olliges http://www.cheynehoran.com.au/starfin.html 
Ben Lexan’s winged keel design was a very clever rule beater. Under the 12 Meter measurement rule if you sacraficed draft you could gain sail area. By placing the majority of the ballast in 30 degree angled wings at the base of a shallow draft keel, Australia II was able to gain sail area. That along with the first fiberglass hull in 12M class which allow Lexan to get the weight out of the ends of the boat and into the lower more centralized Center of Gravity made a dynasty fall. But, I’ve never been convinced that the same shape can benifit a surfboard.
I wrote this below and from what I’ve read above I’m not sure everyone is clear on what I mean by resistance so I’m reposting it here. It’s easy to complicate a simple idea. Resistance means: The resistance of the rail and the outboard fins to the wave face. That’s all. A thick rail resists more than a thin rail. A large fin resists more than a small fin. If you were to have a very thick rail in the tail and a thin rail in the nose you would tend to bury the nose of the board through turns more than if you had a thin rail in the tail and a thick rail in the front. The larger the outboard fins are the more they resist. So the balance of resistance is shifted forward with a larger fin. Smaller outboard fins shift the balance aft. That’s it. Take a batch of fins with you to the beach and try this out. You may disagree but I’m right. After 25 years of being aware of this, it works. There are a number of other important issues but these two, pitch and resistance, are the two that make the most difference.
In regards to the fins/fish/surfboard connection the fins/tails of various undersea creatures are dynamic. If you examine the bone structure of a dolphin for example, you see that their pectoral fins have essentially the same bone structure as our own arms and hands. They are capable of changing the angle, camber and foil at will by bending or extending their “finger” bones. A flex fin (paddle fin or tuna fin style) actually spills energy as it bends. A dolphin can change foils by cupping it’s pecs and tail to redirect water flow into forward speed. Our crude attempts at replicating their speed, grace and style are laughable.
Have any of your rocket scientists noticed that the kids are RIPPING ‘way’ better than the top guys in the 60’s-80’s? The hardest, fasted off the lips possible! The section beating acceleration into airs! 360’s are effortless! On a longboard note, shortboarding on longboards, hanging great tens, tail 360’s! Snap out off it, who among yourselves can pull these moves? Let’s here it… We don’t need a design breakthrough, we need to quit smelling resin and surf more. High Performance surfing comes from your heart and soul. We still rip on waves with 90’s shorboard equipment cause it works unbelieveably well (watch any LOST video). We still rip on '66-'67 NUUHIWA Lightweight outlines with 10" raked fins cause they are the sh@t!!!, and the hottest longboarding ever is ‘NOW’!!!. Speculate all you want, but there are young athletes doing amazing maneuver’s on the current 6’2" x 18.25"x 2.25" with a variety of removeable fins. In the water, fish fins evolved through 100’s of years ‘IN’ THE WATER not in the air or in a machine shop or on a blueprint. My point is, "Unless you actually ‘DO’ advanced surfing maneuvers your B.S. carries little weight with highly skilled surfers. AND for you self-important regional shapers who forget to open a window while laminating, quit fertilizing that Polyp in you sinus, stop rationalizing and go surf. If you were that analytical you would be Pre-MED instead of pre-cancer… No offense to anyone in particular, and please don’t hate me as I outsurf you at your break, in front of your longboard club, on unscientific, unscanned, outdated backyard equipment! Oh yeah…good morning!
I’ve never surfed on one myself but I remember seeing a guy absolutely tearing up windansea about 10 years ago. He was riding a board with one of these fins… obviously it worked well for him. Never say never…
Thanks for that brilliant post Mr. Weed. I am sure that everyone around the Site is waiting with baited breath for more astute comments.
DICK WEED>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>RIGHT ON
Just trying to pass along a bit of knowlege that might help. Sorry for the attempt. Your right. Surfing is just fine and our disposible equipment should never change. By the way Weed, you rip, how many time you beaten Kelly?