Thanks Mark (both): Thank you for explaining you MVG development. And thanks to Mark Vin (Fin?) for provoking some decent discussions recently. You may want to search the archives if you haven't done so already. Fins tend to spark the most heated discussions in surfboard design. Very few of us are hydro- or aero- engineers yet we tend hold on to strongly help positions as though we are. We also seek knowledge from nature and from scientific journals. Most of us take aeronautical information designed for a different media and for much higher speeds and misapply them to slow moving surfboards. I suppose the interest in fins is because they stick out. These little appendages hold are attention and define us as a "type of surfer." In 1985 to ride a single fin shortboard was to suffer ridicule. Riding a multifined longboard now sets you apart from the more traditionalist. When you spot a surfer on the beach we unconsiously look to the fins to try to figure out what kind of person this is. Still the work on fins must continue. They are imperfect: they create drag, they can be dangerous, some catch seaweed and leashes, fixing them to the board has various considerations. Let every Swayaholic resolve to create an innovative fin or two in the next year and report our findings for the interest and betterment of our art. Let's get to work, Rob Olliges
Mr. Vin, The strakes on the F-18 -- are these the cylindrical looking affairs protruding off the wing tips or the long low sloped triangular wing protrusions the begin under the canopy and finish at the leading edge of the wing. I'm fairly certain you refer to the later. Put them on surf fins? Ask yourself: How this would affect direction change? The answer is obvious. the board would be impossible to turn. Bullet like appendages on the end of the fin. No, that's not worth considering. Either addition would be hindrance and unneeded. (Consider lapstrak boats yaw less than smooth hulled boats because the strakes reduce this motion, why would a surfboar be any different. Freedom of motion is the theme a surfboard is built around.) Am I completely amiss and the strakes you refer to something else entirely and my questions those of a cave man? On the other hand fin-lets like Herbs superchargers are very sensible way the imitate nature and accomplish more speed in much the same was the most free, and fastest tuna does. To mantain a proper perspective one must remember that airplane wings do very different things than surfboard fins do. Granted there is a crossover because the lift and drag they both produce are what makes them function efficiently but airplanes are propelled by a prop or by trust in a neutral fluid atmosphere while surfboards plain on a viscous fluid surface and are directed and driven by the fins beneath them the hull shape these fins are attached to. These are very different sets off circumstances to address. One might consider the surfboard a much less sophisticated vehicle than an F-18. In some ways it isn't; in some ways it is. The one that charms you best is the one that holds your eye and is hidden under a most graceful skirt. Mahalo, Rich We reveal what we don't know by what we say.
I agree wholeheartedly in the limitation of the wing analogy - but the tail analogy with the tuna is a lot closer. The real issue is whether MVG has a substantial impact at the speed in question. They could be critical at 50 MPH on a tuna, but irrelevant at 15MPH on a surfboard. I think they are also different from the twinzer or supercharger design. That is more like a double-wing. It allows attached flow at greater angles of attack by having two fins in parallel. Not the same as the MVG, which sets up flow heading into the base of the tuna tail.
blakestah the physics of the tuna swimming motion is a lot more complex than current physics math allows. i have the reports from jennifer nauen at harvard. however i can say that my mvgs work a little different than the tuna finlets, but with much the same result. the tuna has an articulated body, and nature has accomidated this by allowing the finlets to swivel. that is they can move much like a sail on a mast. they can also move individually or as an array. therefore no matter what angle the caudal (tail) fin is in relation to the finlets they can allign with the tail to contribute flow. this differs on a surfboard as the board is inflexible. but the mvgs are inflexible too so they remain for the most part linear to the flow. what little out of line they do get allows them to produce and contribute the micro vortex to the lee side fin and thus contribute flow in the form of a jet into the turbulent bubble reducing drag in a turn. visualize that. next, here's something to ponder. way back in the 70's scientists theorized that according to what was then current theory of flight the common bumble bee could not fly. well obviously it was the theory that was wrong because the bee could in fact fly. basically what they failed to realize at the time was that to the bee air was like a viscious liquid. so while yes the tuna goes 50+mph and the surfboard 15-35mph one may question the effect of the mvg on the lower speeds. well i say the tuna has to go through a full range of speeds from 0-50 and i believe the finlets assist at all levels of this speed increase and maintenance. maybe it's our theory that has kept surfboards from reaching the 50mph mark. but perhaps everyone is completely satisfied with their current boards. keeping in mind that the tuna has a lot of other things going on that assist in swimming, too complex to mention here, there is one test that would be telling. how fast can it swim without finlets? given that the latest research indicates that fish can feel pain i doubt this test will ever be allowed. but if the tuna doesnt need them why after 4 million years are they still there? regardless here's one statistic for ya'll, the atlantic bluefin tuna has been clocked at speeds in excess of 50mph and water is 800 times denser than air. also, it's not nuclear powered and doesnt require a crew of 200 highly trained sailors and techies to operate. that's enough for tonight, but i leave you with this one final thought, today i got a request from mvg team rider, aerial pioneer, and inventor of the air 360 john holeman who just today asked for more mvgs because he's back in the water and surfing again. honestly i and a lot of people besides myself prayed for this day and i for one couldn't be happier. mark
Do you put your MVGs on the side fins of a thruster? If so, in line in front, or to the side? Or just in front of the center fin?
Super stoked to hear John is in the water again. Soon to be seen in the skys above Sebastian. Rob Olliges
tubedog john holeman rides twins, so there is no trailing fin for him to put the mvg in front of. however, a couple years ago john came up with the idea of putting one directly in front of and in line with each of the side fins. he put them about a thumb width in front. john said he gets at least 15% more speed, faster acceleration and better recovery speed after landing an air. i finally tried his set up a couple weeks ago. (i'm a a slow learner. lol.) i have a 2 1/2 year old greg loehr tfs twin fish and i had taken the mvgs off to repair a cracked fin box and decided that instead of putting the mvgs back where greg originally did i would try john's idea. it was fast, tracked high very easily, turned easily (too easily at first but i got it down) and because it tracked high and pulled the max speed off the top of the wave i could see why john liked it set this way. so there you have it, tubedog. mark
Mark, Glad to hear John is doing so much better. Somehow I knew he couldn't be kept down for long.
What is your positioning of mvgs on the side fins? In-front in-line, or off to side? If to the side, how much away from main side fins? Thanks-
So you'd presume the MVGs on a tuna are there to aid water flow heading into the tail... and not to promote reattachment of flow coming off the rapidly tapering body height in the rear half of the fish? http://www.flmnh.ufl.edu/fish/Gallery/Descript/BluefinTuna/BluefinTuna.html This is kinda important - the vast majority of MVGs are rearward of the leading edge of the foil. They act on flow re-attachment in the draft or rear of the section, where water needs to re-attach. In airplanes, they disrupt flow at the leading edge, so that it is more disturbed coming off the rear of the foil, and separated flow is minimized at steeper angles of attack. http://www.microaero.com/pages/v_howvgswrk.html I kinda think the tuna MVG fins are there to promote re-attachment for water coming off the body, and have little to do with the actions of the rear tail.