Fin Cant

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Anonymous (not verified)

How important is fin cant to all you board builders out there? Should the same angle be used for all the different bottom contours out there? I know how it affects a boards performance, Just want to see what you guys think! After some responses, i'll tell why I'm asking!

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[email protected] (not verified)

From talking with different shapers from different areas, steeper faster waves work better with less cant (5 degrees) and slower slopier waves more cant (7 degrees). But, there are numerous other parameters you'll want to tweak besides fin cant when switching from one wave type to another.

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STL (not verified)

I saw a friends quiver of rawsons, and noticed that there was a "6 degrees" written by pat, on the stringer of the 6'2", but 5 degrees written on the guns. I'm assuming this is for the fin guy right? Don't you think all shapers should do that! Seems the shaper would know better, than the fin guy.

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surflab (not verified)

As far as writing it on boards, Most shapers dont have a clue, on about 25% of the boards I glass, I have to go asfar as mark and place the fins myself. Some of the more experienced will tell me. some will tell me to tell me and really have no clue. I know in bigger shops when the models come through, say like A CI FLYER, gets 6 degrees its pretty standard http://www.surfboardglassing.com

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Bert Burger (not verified)

fin cant is hell important as well as toe in ..it must harmonize with the overall design package of your board you can have the best board on the planet and totally kill it with poor choice of toe in and cant even if there set in the right place....my toe in covers 4ml to 10 ml depending on speed of wave and cant covers 5 to 20 degrees, and theres some combinations of cant and rocker that can get real ugly...a bad combo of cant and tail rocker and your board feels like its towing a chunk of weed....your fin cant can also be responsible for your rail digging if combined with other rockers and outlines....like i said before ,,,the whole package must harmonize and fin cant is just another of the variables.... regards BERT

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Keith Melville (not verified)

4 to 10 ml of toe in? do you mean 4 to 10 mm?

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Anonymous's picture
Bert Burger (not verified)

yep ,,sorry typo

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Keith Melville (not verified)

no problema, it was either that or you'd figured out how to measure toe-in volumetrically... theoretically possible I suppose (angle of toe-in times surface area of fin)? what sort of set up would cause you to use 10mm? (extreme end of your range)?

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blakestah (not verified)

I don't believe in altered toe-in on a thruster. I've had numerous guns with the toe reduced, and they all turn for squat. Then I got one with normal toe-in, and slightly smaller side fins to reduce drive and promote speed, and it works really well. This is generally what tow-in boards use, too, smaller side bites. Too little cant and your rail digs, too much and you lose drive, but ride high through turns. It's a good bit less sensitive than toe-in, through, where a two degrees radically changes the ride. http://www.blakestah.com/fins/

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Anonymous's picture
Bert Burger (not verified)

i increase the tow in for big waves to reduce the lift and also the fins have a more favourable angle of attack...i decrease the cant as well so you dont end up flying ,reduce the thickness and pull the camber back and make em a little smaller as well other wise you feel over finned and if its serious size then do 20% 80% foil on the sides as well but thats just probably compensating for the fact that at that size i really need a single fin...but i cant help myself i still wanna turn ... regards BERT

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Eric (not verified)

Bert, when you say "pull the camber back" do you mean putting the maximum thickness of the foil section from say 25% to 30%? I'm going to grind out some thrusters soon. I'll chose a foil section that looks good and makes sense as compared to the surfing standards. I have to clarify that I'm grinding kiteboard fins for surf use, but not surfing fins. We are most similar to towboards except we "tow" with wind instead of gasoline. Of course, we can't let go of the kite for a totally free experience. Eric

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Krokus (not verified)

Great thread but I still havn't seen what I am after. I have been using about 4.5 degrees of cant on my standard thrusters. I have also been aligning toe-in to a point 3" each side of center @ 12N (12" back from the nose). My theory there is the angle is more relative to board length. Our waves are generally head high or less and rather fat. Most of the time we have wind chop also. I am gathering that I can increase the cant angle to say 6 degrees and this should help with the slow choppy conditions. My standard rails are med/hard @ about 25/75. Had one rider say board was super "loose" (6' 4" with 4.5degree cant, slightly less toe for drive but increase tail rocker). Its all a compromise in efficiency. Jim's dissertation on dynamics was really great information, thanks Jim! Now how about the cant, what effect does increasing and decreasing have when all else stays the same?? Krokus

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HalSose (not verified)

Toe-IN: >My theory there is the angle is more relative to board length. Correct up to a point, but no Cigar! Not so much board length, but "Expected Wave Size". Longer boards surf bigger waves. Smaller boards smaller waves. Thats why the string on the nose to the fins has always been such a decent trick for aligning toe-in. More toe-in on the smaller boards for ......smaller waves. Less toe-in on the larger boards for ......bigger waves. If you were to create a Super Board that was 5'10" that you used exclusively for big days you'd want 'less toe-in'. Conversely, if you made a 7'1" that you wanted tuned for smaller waves,......'more toe-in'.

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Bert Burger (not verified)

yep eric thats the camber move it forward for small waves back for big waves ... krokus if that was me in those waves id say 15 degrees of cant no tail rocker behind the fins. all that cant will lift the nose making it easier to throw up onto sections and over mushy bits but because itll lift the nose itll make the tail sit down, so flat behind the fins means that as the tail is being pushed down itll squirt ..it will be hell slipery in o h waves but in small stuff real drivy off the tail and great around sections where you want just go straight up after youve got around it...throw in a little more outline to compensate for tail rocker halsose have you tested those theorys???????as well as testing that theory i would also suggest a book from the libary on the physics of foils then it will make sense....you probably wont find a book like that ...maybe something on plane wings will do... regards BERT

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HalSose (not verified)

Bert if I have it wrong , please explain. I do double duty as a student and sometimes a teacher. Let me have it....I can take it!

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Anonymous's picture
Bert Burger (not verified)

ok i will try my best ...buts its a hard thing to explain in few words...side fins on boards are basically like plane wings....so if you imagined a plane or a bird droping nose first and then pulling up real hard, those same angles of attack are being thrown at your side fins ...when you turn your either turning off one fin or the other ...anyway back to planes ,if a plane is flying along and then suddenly pulls up the angle of attack on the wings is increased ,which in turn increases lift but if the angle of attack is to great the wings fail to keep lifting because the air traveling over the top cant stay attached to upper surface and starts to break away in turbulence and cavitations ..its commonly known as stalling and when pilots are learning to fly they have to know how far they can push there plane safely or else itll fall out of the sky...in a surfboard its called pushing hard into a bottom turn if you push to hard your board slides out,(the other design aspects of a board have an effect here as well but for now its just fins were talking..) what you are doing when turning is changing the angle of attack on the fins...as you change the angle of attack the fins produce more lift but not lift in vertical sense ,but at 90 degrees to the foil ....thats what hooks you into a turn, get 2 boards identical one thruster one single the thruster will hook way easier coz of the foil on the side fin ... now when we change tow in were changing the point at where the fin will have enough angle of attck to actually start turning your board,,,,if your fins are parralel and your going straight and you have decent foils there will already be enough angle of attack to create lift ,only problem there is ,there pulling against one another...coz one fin is pulling or lifting one way and the other fin is pulling the other way, your board becomes super twitchy and responds to very subtle body movements .......but if you turn to hard itll slide out earlier coz of the greater angle of attack on the fins due to less tow in ..now if we towed our fins right in like 10 mm it would be like a plane flying along with the body straight but the wings tilted down, theres no lift at all, before the wings had enough lift to make the plane pull up ,the tail of the plane would be hanging right down ....so when we tow our fins in we have to turn our board further before the fins pick up the water and start to pull us around,but what that means is that we can push our board further again before the fins fail and slide out ... less tow = more sensitivity less hold more tow = less sensitivity more hold add to this one more thing and thats speed ,the faster you go the less angle of attack a fin or wing can tolerate before it fails (just like if you turn a corner in your car, go slow and stick to the road ,go to fast and you slide out,each individual water molecule has mass as well if its made to go around the leading edge of your fin to fast itll slide out crashing into its buddy and starting a chain reaction of turbulence and your sliding out of control) so you can see why a big wave board needs more tow in 1 is you dont want your board sliding out if you push it to hard ,,,, 2 is the extra speed means your fins are likely to fail at a lower angle of attack ... how was that halsose ? it took me years to get a handle on my fins and exactly what they were doing...so if my explanation helps you understand a little better that will be good .... regards BERT

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[email protected] (not verified)

Bert, I often agree with most everything you say. I paticularly like the part about too much tow and your fins are going to act like a planes wings pointing downward and plowing along. (Something the Future Vector diagrams seem to totally disregard) But, I would emphasize more about the lift coefficient pulling your rail down and giving you something to pivot about. Also, fins that are parallel to the string with a 50/50 foil and camber at 30% or greater back from the leading edge are going to track. That's why the old school fish used to be great down the line point break waves. But, were hard to get vertical on. Toe is used to setup some initial instability so the board wants to turn. Toe, cant, camber, rake, base area, depth and tip area all have to be considered when determining the average flow rate across your fins and rail. More cant, larger template area with forward camber 20-25% will generate more lift at lower speeds. That's why we make the XT-1's with a fairly vertical template and the camber forward and thick and use a tiny trailer fin to be used in wider tailed boards and softer waves. But, they will also create more drag at higher flow rates. The X-2s are made to be a higher speed fin with the camber farther aft and a smaller template. So, they are probably best used with less toe and cant(5-6 degrees)in narrower tailed boards. As the velocities increase to the speeds that tow in surfers are reaching you want less drag and more inherent stability so the fins get smaller the camber is farther aft a 20/80% leading edge curvature is utilized and the toe is reduced all minize drag and turbulence. So, considering how much of each of the variables is necessary is super dependent upon how fast you plan on moving through the water.

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STL (not verified)

Something else the futures guys overlooked, was being able to have SOME, or how about ANY control over the cant of the fins. I've seen many installers putting those boxes in with no install fins. They just tape them off, and slam 'em in. Angle/cant?...anyone's guess. Center fins straight? Anyone's guess. Correct me if I'm wrong, but in this age of modernization of the surfboard, coupled with most production guys on the shaping computer(for accuracy i'm assuming), this seems to be huge step backwards IMHO. Cant was being measured accurately with glass-ons for decades. Shouldn't a fin system have cant that's at least checkable? I think so.

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HalSose (not verified)

Thanks Burt, give me some time to digest this...... i.e. read a few times.. in the meantime , someone has already disagreed, and I've wanted to restate my example.....since I think my outrageous example probably caused problems..... what I know of toe-in relates to the original Twin Fin Fish. No toe-in , it would track. toe-in: it would strengthen the boards rotational pt. , as in a pair of ski's going slow downhill and being able to rotate at your hips to pt. the ski's. i.e. No tracking! As to my previous example it was an Extreme Example, perhaps the example would have been better stated as...... If you have two boards each 6'4" and want one for larger waves and one for smaller waves and the only variable you can change on each board is the toe-in, ....then the small wave board should have more toe-in, the big wave version less. Anything wrong here! I'm thinkin not, but my previous example was like two boards er ahhhh.... dont remeber, but like 6'1" for big waves and 7'1" for small waves and that probably caused more confusion than it did to clarify.

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KR (not verified)

I'm definately no rocket scientist, I only relate my info to what I feel when I test ride my theories and my theory with big wave boards is that you need more toe in because the rockers and outlines are longer and if you want that puppy to turn you need to toe in those fins as for smaller waves i find the opposite, the curves are shorter and the outlines have more curve so you need to get some distance (squirt)out of turns over flat sections and if your fins are toed in to much it feels like you are pushing water. All that this proves is that there is more than one way to skin a cat. You can play with all the major keys (outline , rocker, foil, fins) to achieve different reactions thats why there will never be one surfboard or fin template. KR

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Bert Burger (not verified)

kr is right on there...tom that was sick ..as i red through your post it was in logical sequence man thats brilliant to know that others out there really understand the dynamics of fins...i was impressed....another thing to consider on big wave boards is when you increase toe in even tho your inside fin starts to hook a little later because it takes longer before the angle of attack is enough to produce lift....your out side fin is actually producing some lift as well first...if your foils are good ...a plane can fly upside down it just needs way more angle of attack to produce lift....as far as the drag is concerned its not a bad thing coz you end up shaping other things in as well to produce some drag but give some control at those high speeds....as for as tow in surfing is concerned....there at the next level again with different needs .... ps i made some jigs that fit into the futures boxes to line them up...there boxes are great but there fins havent really got it yet ....i make my own and mold the bases to fit the boxes.... regards BERT

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Anonymous's picture
Bert Burger (not verified)

tom just want to clarify some points?????im pretty sure were in agreement 99%of the way and so far ive never read another thing on fins that shows as much understanding as what youve written... you said.. "tow is used to set up some initial instability so the board wants to turn..." in my first example i used a board with no toe in at all i think that might have thrown you ...i would never build a board with no toe in .it tracks mainly due to the fact that both fins are pulling on the board in opposite directions,but it also doesnt know where it wants to go it tracks and is out of control at the same time ,its super sensitive ,sometimes will go in directions you dont want it to just coz your weight isnt right..... by having toe in your making sure that the bulk of the lift is coming from your inside fin.and that your well into a turn before the fin kicks in ...by having no toe in your board,it reacts to every little stimulus even whats under the water, the feeling of tracking comes from the fact the board doesnt do what you want it to... the toe in means that as your inside pivoting fin is producing lift your outside fin is like a plane wing tilting down producing no lift ,but once your turn tightens a little more your outside fin does start to produce a little lift but in reverse like a plane flying upside down.....give it just a few more degrees of angle of attack and your outside fin starts to fail and cavitate but usually by that time its out of the water anyway....as long as your inside fin is doing its stuff your well and truly in control.... having toe in offers more straight line control coz your fins arent pulling against one another and when you do turn the inside fin is doing most of the work....so any way after all that wouldnt toe in offer more stability and control before you start doing a turn???? when you were talking about the X2s you said a little less toe and cant.....i fully agree with less cant ...to much at high speed and your board starts to rise out of the water like your taking off in a plane....i do disagree with less toe because because at higher speeds the same angle of attack can cause a fin to fail whereas at low speeds the same angle of attack and the water is still wrapping cleanly around your fin...when you use more toe in on your big wave board you actually soften the angle of attack on your inside fin thus making it hold in better when your fully loading a turn....even tho your outside fin starts to create drag a little ealier youve still got control and hold ...that out side fin does create some problems ive been working with flex bias fins to help overcome that problem but not completely solved....even tho i ride thrusters in everything, the old single fin eliminates some of these problems at really high speeds and i really havent done enough work with them in big waves coz im always leaning towards thrusters trying to make them work....what you said about the XT-1s was so right, you nailed every aspect of whats happening....i only got 1 slight modification i would recomend there ...the more vertical template will offer more hook in the early stages of the turn but doesnt seem to drive out the end of the turn as well ...a little more rake will soften the intial stage of the turn but offer way more drive out the back of the turn which is great for real soft waves ....the more vertical template seems to turn and stop if the waves are to soft.....but in juice offer sick hook in the pocket at high speeds...and if its good juice theres no problem with drive out of the turn coz your falling out of the lip anyway...... ok lets see if we can figure this thing out....i may be missing something ,im pretty sure ive got it worked out ,i may also have misinterpreted what you wrote..... regards BERT

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[email protected] (not verified)

I understand your angle of attack arguement. And, on the foiled side it seems to make sense. But, on the low pressure side the more toe you induced the larger the shadow, which equates to more turbulence and drag. I think where we are diverging is in the intent of the design. Big wave guns for surfing Sunset and Cloud Break over the years have gone to more performance style surfing and require fin setups that can handle a greater range of angle of attack. Primarily because people are snapping under the lip and doing big carving cut backs in waves that previuosly we all just ran for our lives. When tow in surfing started people were designing their boards with the old run for your life survival mode and toed their fins less and went with finer foils and camber aft. Now, when I talk to tow in board makers, they are already starting to want bigger fins with more toe and camber slightyly forward. The tow in guys are starting to get away from the run for your life mode and more perform on the face mode. Now as far as how we make the XT-1. A vertical template is a relative term. The XT-1 is such a large fin that the angle from the leading base to the trailing tip is not as shallow as say our X-3 template. The X-3 template with its full size center fin gives you that softer entry and more drive out of the exit feel. Personally, it's a bit tracky for the way I like to surf. But, thousands of people riding Al Merricks seem to like the template. So, to each his own. I personally prefer our X-4 template for my side fins and an X-1 or X-2 center fin. I ride my thrusters with a 50/50 weighting and only weight my back foot heavily in extremely steep stituations. So, I like a larger, more vertical template with relatively vertical rake, camber forward, medium toe and about 7 degrees of cant for my side fins and a fine smaller center fin for my general purpose thruster. It's got a 14-3/8" tail and farely flat rocker and gets ridden at Lowers alot. But, when I surf places like the Reefs in La Jolla, I like to ride my Bonzer of a vary similar template and I ride it hard off my back foot. When we setup are fin range we attempted to bang the corners of contemporary fin designs first utilizing the the master templates and foils of established shapers. Maurice Cole gave us the X-1 and X-2 templates. That's part of the reason the camber is farther back on his fins. Australia typically has more powerful waves. Al Merrick gave us the X-3 and the X-7 to match. Timmy Paterson gave us the X-4. California shapers tended to give us fins with camber forward. T&C gave us the X-5. Again Hawiian waves camber aft. The X-6 is a modification of the X-3 that we did for Taylor Knox. The X-8 we did from a master of Casey McCrystal. The XT-1 we did from a master of Matt Biolas. Guy Takyama gave us the XL-2 master. And, Malcomb Campbell gave us the masters to do his Bonzers. Almost all our templates are also available in laminated fiberglass and we are expanding our RTM range as well (3 templates currently available). We are planning on adding some new templates based upon some pretty extreme design theory. But, we been covering some other portions of business recently and hope to get back to Red X real soon. We can only afford to spend so much time a year developing Red X. In the end everything in surfboard fin design is a compromise and you just have to tweak your variables until you find your comfort zone in the spectrum of board design.

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Anonymous's picture
Herb Spitzer (not verified)

.........I only let my glassers do the lam/hottie/and ruff out.This allows me to control the boxing(Red-X) and finish work...........nothing like getting back a board you didn't shape.Herb

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[email protected] (not verified)

Bert, I forgot to address your question about inherent instability. There is a turbulent zone immediately beneath the bottom of your board that varies in depth deepending upon surface condition, bottom contour and velocity. When your board is parallel to the surface of the wave your fins are feeling an equal amount of influence from the various densities that the fins are reaching down through. As soon as you start to initiate any type of turn the inside fin is emersed deeper into clean non-turbulent zone and the outside fin is immediately in a less dense flow over the depth of the foil. Consequently, the inherent instability and a good reason to surf a thruster rail to rail and not try to glide in the flats.

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blakestah (not verified)

Bert, I feel compelled to explain why I recommend not changing toe-in angles. I agree, that toe-in creates drive. I do not think assymmetric foils are at all required, although they do help. Singles cannot drive simply because the center fin is parallel to the stringer line. An analogy is a sailboat trying to tack with its sail aligned with its keel. It doesn't move real fast. The sail angle relative to the boat centerline is critical. Anyway, back to toe-in. The center fin is aligned with the stringer line, on a thruster. It provides hold. It is there to stall, and yank the tail back in line, when you try to turn too hard. The relationship between the tail fin stalling, and the side fin creating drive is critical. For this reason using smaller side fins is more effective in a "faster moving" board than reducing the toe-in. Reduced toe-in just makes the board more tracky and all around crappy to try to turn. In a very straightforward analogy, the rear fin acts as a canard to the side fin. When you turn. the rear fin stalls. In stalling, it engages forces on the hull to protect and prevent a side fin stall. Because if you stall the side fin you've lost all directional control, and at best you can skid stop if you are really really good. If you assume the thruster fins MUST always be the same size, you can reduce toe-in on bigger wave boards, but it works much better to keep the toe-in angle the same, and make the side-biters smaller. http://www.blakestah.com/fins/

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Anonymous's picture
Bert Burger (not verified)

ok ....thinking caps on ....remove all outside stimulus .... first tom ...the foiled side is the low pressure side ,the flat side is the high pressure side....bernoulis work with fluids contributed greatly to others after him because he discovered the principals and laws present in fluid flow....principal number 1... when the speed increases the pressure decreases.. blakestah....i increase toe in on big wave boards so the side fins produce less lift...and you are totally right in putting smaller side fins in coz that'll reduce the lift as well ...both methods will produce less lift from the sides....the idea of producing less lift in your sides on big waves is for more control and to stop your board over reacting.....because a fin will produce more lift as the speed increases ...and that increase in lift is logarythmic to speed ( example imagine you straped a square foot of ply wood to your hand ,went driving in your car and hung your arm out the window at 30 mph your hand would fly along, tilt your hand a little to increase angle of attack and you get extra lift your arm lifts up....now do the same thing doing 60 mph (dont do it!!!!)your hand still flys along , but when you tilt your hand to increase angle of attack it will produce enough lift to hurt you ...so doubling the speed more than doubles the lift...) you said that the side fin creates drive ( i may have taken that out of context)...yes the tail fin and sides together create a vector sum...more than one force acting on an object....the sides dont create as much drive as the tail fin ....remove the tail fin lose drive ...the tail fin on a board works similar to the tail on a fish ,,,if a fish had no tail fin it cant accelerate...it would just flap from side to side like a twinny without forward drive....but if the tail fin was to big it would overpower the fish, now when the fish wiggled its tail, the tail would remain relativly still while the fishes body moved ,,,, on a thruster you can work your tail fin from side to side to create drive ...it didnt get the name thruster for nothing.... your pivoting off your fronts driving off your tail...its very important your front fins have enough bite to make your tail fin effective...classic example is keel and rudder, keel is pivot point,rudder makes drive and direction ,remove the keel and you remove the pivot point now when you turn the rudder, there is no direction change and no drive forward,,, even tho these examples are crude in comparison they are similar enough to be used to grasp a bit of whats going on....imagine if you had small keel and huge rudder , the rudder would overpower the keel, when you turned the rudder it would want to remain on track ,while the keel now was receiving an angle of attack as the boat crabbed,if the angle on the keel was to much it would cavitate and fail to act as a pivot point,,,,,.... if your side fin fails you slide out .if your tail fin fails you spin out ,because your pivoting off your front fin.if your tail fin is to big in comparison to your front fins it then becomes the pivot point and your body weight must get behind the tail fin to do an effective hook under the lip.... if your tail fin is to small in comparison to your fronts(big fronts) you get heaps of hold you have a pivot point but not as much drive forward ,just like if you had a tiny rudder it wouldnt be as effective.... in short, small fronts big tail = more drive less direction.... big fronts small tail = more direction less drive... theres a balance to be acheived for different speed waves ,,, and like you say blakestah they work as a package.....

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[email protected] (not verified)

Bert, I usually think in terms of sails, when I'm considering angle of attack. When going up wind, the closest even an IACC boat can sail close to the wind is 25 degrees apparent wind angle. Inorder to achieve this they sheet the sails in tight which moves the draft aft and flattens the foil. In this configuration the sails produce a fraction of the drive. But, they allow for an angle of attack that is closer to head to wind. Think of the leading edge of the sail or foil as 0 degrees. The sail or foil works on its high pressure on the flat side and low pressure on its curved side as long as the angle of attack stays between 25 degrees to 90 degrees. (Let's forget about the fact that headsails are not sheeted to the centerline of the boat for a moment, because even mono-rigs which are sheeted to the centerline can't exceed 25 degrees AWA). Anyway as soon as you try to point higher than 25 degrees apparent the sail starts to luff(opposite of stalling). Luffing is the point at which the air flow seperates from the windward side of the sail and the majority is going around the foiled leeward side of the sail. The low pressure side becomes the high pressure side and vice versa. I understand that sails are soft and rely upon the flow of air to maintain their shape. They are also much more sensitive than a ridgid foil and require greater angles of attack. But, they are a good visual for what I'm trying to communicate. Back to surfboards. Until the flow of water is running parallel (or close enough that laminar flow bends the flow) to the flat side of the fin, the fin will produce less and less lift and more and more drag. The foiled side becomes the high pressure side and the flat side becomes the low pressure side. So, until you are initiating a turn, your just dragging those puppies around. And as you initiate a turn the outside fin looses more and more ability to create lift as the inside fin is creating more and more lift up to the point of stalling. Hence my statement about inherent instability. Thrusters are built to turn. Singles are made to glide. Thruster are intended for controlled redirections close to the power. Singles are meant maintain stabilty and glide within a much tighter angle of attack envelope. Two different tools for two different kinds of wave riding.

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blakestah (not verified)

I hope my point is not getting lost. It seems easy to all agree that for reasonable turns there are two real active fins on a thruster. My point of view is that the side fin is generating drive. Physically (to take tom's sailboat analogy), drive is impossible with a fin aligned with the stringer line. It requires an angled side fin, and a "stringer-line" angle of attack (AOA) JUST GREATER than the angle of the side fin. In this configuration, the side fin has forces forward along the stringer-line (drive), and towards the rail. In the same configuration, the center fin cannot ever generate any force up the stringer-line. It is like a sailboat trying to tack with its sail aligned with its hull (and tightly drawn). The sailboat goes backwards, only. Similarly, the center fin can only generate forces to the sides, or rearward. Never forward. My viewpoint/theory/argument is that the relative angle difference between side fins and the center fin is EXTREMELY important. It should not be changed for big wave boards. Because, once you get into an AOA in which the side fins generate drive, the rear fin starts to stall. This is a canard configuration. If you attempt to further increase the AOA, the rear fin will stall more. When the rear fin stalls, it generates a force backwards from the direction of motion. Because of its position, this tends to straigten out the turn. This is a "turn protector". It is truly possible to generate as much drive on a twin as on a thruster, but it is much less stable through the turns, because it lacks the rear fin. You need the relative angle difference between side and rear fins to maximize hold and drive through turns. If you make the rear fin larger than the sides, you can generate less thrust when you go rail to rail. This occurs because the thrust comes from the side fins and NOT from the rear fin. The rear fin is there to provide "hold". If you make it a little smaller, the board can generate more thrust worked rail to rail. http://www.blakestah.com/fins/

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Anonymous's picture
The BUZZ (not verified)

"A 'thruster' has three fins going in three different directions which create substantial drag and loss of speed, because at least two of the fins are constantly out of alignment with the water flow. With a self-aligning rear edge, speed is significantly increased because the fins are allowed to respond to the water pressure and continually move into an improved alignment with the water flow. When the rear edge of the fin responds to the water pressure against it, higher speeds are achieved, turns are initiated easier and the board becomes less prone to spinning out while the spring like effect of the "loaded up" rear edge can be used to generate more speed, more drive and more lift through turns." George Greenough http://www.speeedfins.com/history/

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Anonymous's picture
Herb Spitzer (not verified)

.......My systems with tri or twins product almost no drag,and maximum contollable lift = much more stable,and looser than the standard 2 or 3 fin set-ups.Not to mention riding it straight inline(trimming,gliding) w/ rapid gained excelleration(no pumping or rollercoasting). .........Paddling in a pack of surfers against a strong current proves this to me,as I can out run even the longest flatest single fins,etc,on a deck w/ 1/2 the volume,and plane length. ..........an E.O.D. saying,"if you see me running by you,you'd better catch-up!Herb

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Anonymous's picture
Bert Burger (not verified)

question for tom...i can understand the side fin generating less and less lift as the water flow becomes more parralell ...but why should there be more drag......? to me it sounds like your foils are to thin...and your leading edges on the inside flat side are to sharp so when water is forced onto the high pressure side its not wraping the leading edge cleanly but is breaking away ,creating turbulence and drag... question for blakestah ...how come a twinny without a tail fin can hold the face so well up high???another question can a centre fin generate lift???? remember the vector equation ...take each variable (what each fin is doing separatly)and then add them.then you get one overall force in a given direction.. im starting to get the feeling no one is wrong here....it seems like we are all observing slightly different outcomes because we not all working with the same variables.... regards BERT

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Anonymous's picture
blakestah (not verified)

Herb, there is absolutely no way you can claim substantially no drag with your modified thruster set-ups, Herb. I suggest you take out all the fins and paddle around, and check your observations. I've taken several surfboards that were thrusters and retrofitted them with my rotating single fins, and the differences in speed are notable, both when going straight, and when turning. Thrusters are not a low-drag configuration. I'd be happy to send you (or Bert) one of these systems to try if you have any doubts at all. A relatively full description exists at the web site below. To clarify the theory on thruster drag, when going straight, the two side fins each deflect water out to the side. This creates a void in the middle, and will cause a large, slow, eddy current that creates drag. Speedfins are not much better, they do not really turn very much. http://www.blakestah.com/fins/

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Anonymous's picture
[email protected] (not verified)

Bert, I'm not talking about a specific fin in the above referenced angle of attack arguement. I'm talking about single foiled fins in general. Our fins are actually quite full incomparison to the laminated fins. Glass filled nylon is lighter than laminated polyester resin and fiberglass cloth. The extra girth also gives us a stiffer lateral resistance. But, that's in general. We do have some thinner fins. And yes, the leading edge of our fins is abit abrupt in its transition from the foiled side to the flat side. But, that is because it is easier to remove material than to add on plastic parts. Meaning some people like nice sharp transitions. Others want a full radius leading edge. Anyone can sand a radius into our fins. But, it's quite another thing to attempt to glue an edge back on. But, I know in this day of instant gratification fewer and fewer people want to touch a tool and tweak things in themselves. But, that was our logic when we originally made the fin molds. The point I was attempting to make is that since side fins are intially toed eskew to the stringer. And hypothetically the flow is parallel to the stringer when you are not turning the flow vector intercepts the curvature of the foil prior to the appex of the transition between the two sides of the foil. Consequently, a greater percentage of the flow is going to follow the foiled side and a greater seperation is occuring on the flat side until that flow vector is changed to at least parallel to the apex of the transition between the two sides as it is changing angle towards the flat side. What I'm attempting to describe is that intuitive feeling that thrusters drag when gliding flat and straight. But, light up as soon as you start initiating turns. The inside fin becomes the working fin and the outside fin just negates itself. Depending upon the speed you're traveling at determines how much you want to fillet that flat side edge and smooth some of the twitchieness out of the transition.

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Anonymous's picture
Herb Spitzer (not verified)

......it is like I stated,at least for me and some others that use my SCs and/or+mvgs = CrossXfire system. .........TRIs or TWINs aren't suppose to go straight down the line and gain maximum speeds either,but I can do this very easily/thoughtlessly.In other words..................it changes the whole ballgame completely. .........As far as testing with or without fins,SCs and etc.,Yes I done this several times and my way feels almost as drag/cavitation free as completely finless board,yet has more stability,looseness,and speed/forward drive than anything else I've ridden including singles or thrusters..........and I have ridden just about everything that floats. ........I would like to try your rotating fin.I have tried rotating fins before(Waltie swivel fin)and found some real plus' to them as well as some big down sides.Frontside they worked fantastic,but backside the waltie swivel fin tended to hang me up due to the fin reversing angle creating a water brake.Now this might be due to the nature of my backhand style,I don't know.That's just what I learned from R&D ing them...........your fin system seems simular,are you aware of the waltie fins,I still have a couple.Herb

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Anonymous's picture
Herb Spitzer (not verified)

......have a nasty backlash,like when doing a full roundhouse cutback they tend to create a whip maybe a couple times thru the turn,really wierd.Down the line they do pump up energy more/faster/better.I also exp. the backlash in other incidents.As much as I tried to predict,control,backoff or drive thru it,I just could get a full 100% grip on the backlash thing,and sometimes the backlash would jump up in a split second in the most critical situations........not fun.Herb

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Anonymous's picture
blakestah (not verified)

We have found rotating fins take perhaps 5-10 good sessions to work out all the kinks in performance. I have not been able to find a Waltie - I would like to see it. The main differences vary from user to user. Better surfers have to unlearn rail-reliance in making turns. I still sometimes pound a rail into a turn, only to have the board fly out from me. It turns harder than a thruster, but the way you enter and leave a turn is a little different. Email me blakestah AT blakestah DOT com if you want to try a freebie, I'm looking for feedback. The website link describes what we've found so far. http://www.blakestah.com/fins/

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Anonymous's picture
Herb Spitzer (not verified)

.......I'll trade you a waltie for it.The waltie may be used, but 100% functional/clean + all parts included....deal? oh yeah, I used the waltie for several weeks into months and switched it from board to board.Herb I'll email you as soon as I get back from my daughter's conference at her school.Herb

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Anonymous's picture
blakestah (not verified)

A waltie for one of my fin systems is a fine deal by me. Drop me a line. http://www.blakestah.com/fins/

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Anonymous's picture
Dave Verrall (not verified)

hey blakestah, i just checked out you site with the pic of the fin.. i have about 10 sets of these put away in the roof of my factory, i bought them about 10 years ago from a guy who spent a fair bit of money with his dad making the moulds etc, i think his name was simon, he was from brisbane and did cheap backyard quality boards out of his van. the fins workings are very similar to yours, we found them a simple novelty, no real performance was gained. luke egan tried them and said NO. one of the boards i made comes back for repairs every now and then and that customer loves it. however i rode mine for around a month and found i liked the board better with a wedge stuck in it to stop it rotating. i will try and find a set and post a pic for you to check out, dave http://www.feraldave.com

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Anonymous's picture
Bert Burger (not verified)

very enjoyable conversation guys .....tom im stoked to think that a guy like you who actually understands fins is in the bussiness of making them.....i was impressed with fact you answered every comment of mine with the specific information and stuck to the subject not a marketing blurb...your the sorta guy i could work with. unlike most guys who stand there with there mouth open,and then come back with a prerecorded statement.... i found it interesting that some of the failings of thrusters that others have observed, have lead them to solutions to overcome some of the shortcomings.... blakestah ....after thinking about your comments today ,the ones about reducing the size of the side fins for big waves ,it seems a perfectly logical way to go....its the simplest way of reducing lift (the overall effect of the side fins).i starting thinking about the sort of waves that set up would work well in,,, solid size ,fast and down the line.... my way of going about big wave performance ,,,was a make the thruster work at all cost mentality...more toe,,less cant ,camber back,20-80 side fin foils,camber forward thicker tail fin,my likes in a big wave board are still very performance oriented,,,, some comments tom made,,,, made me realise exactly why my boards have evolved this way " thrusters are made to turn " "made to go from rail to rail " " made for controled redirections close to the power zone"... even tho those comments are not new to me ,it just emphasises the personal influence in board design ,the shapers own likes in a board will lead him down certain design paths . being a younger shaper myself ,my own surfing likes and dislikes still come out very strongly in my boards for customers....it suddenly hit me ...... a comment by an older shaper to me more than 10 years ago ....he said "once you stop surfing you start shaping boards for other people "..it was like a riddle that i only just worked out.... blakestah i can see your concerns on not wanting to change toe in because of the fact you need more angle of attck before your side fins kick in thus making your tail fin more prone to stalling .my way of dealing with that problem was thicker centre fin and flex bias side fins....that way even when the tail fin is getting real heavy angles put on it ,its still driving you forward,and by having my side fins not bend as much when you load the flat side but bend a little more when you load the foiled side it helps compensate for the extra toe in when going straight along with the 20-80 foils as well, but that extra toe gives more hold when your right on your rail ,,,i have this strong feeling the only thing that lead us to different solutions was our own surfing likes .....hanging out at swaylocks has given way more insight into other peoples surfing likes ,even in just the week or so i been here .... tom ive also been making some real stiff 12 mm thick carbon fins ....they are totally sick in up to 6'waves ,60 grams per set and they float....they can only be made in a vacumn mold ....i been making them since 97 all set fins but lately i been gettin requests to do them for boxes so im gonna have a go at doing a futures box set ....you guys may already be working with real light stuff ,,if your not we should confer,,,, regards BERT

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Anonymous's picture
[email protected] (not verified)

Bert, I'm always happy to enter into an intellectual discussion on design theory. The internet is an incredible venue for bringing together people of similar interests. And, each time we exchange theories, we each come away with a better understanding of how each parameter affects the outcome. Our company is a custom plastic injection molding company. The medium we work in is best for replicating proven designs. We are constantly looking for refinements and innovations that we can help bring to market. Besides making Red X fins, we also make leash connector components, soft surfboard fins, fishing accessories, RV accessories and medical components. One of the medical projects we are currently working on will knock sixty hours of lab work down to less than one to determine the cancerous cell count in blood samples. We rely upon guys like you, Halcyon, Herb, Maurice Cole, Timmy Patterson, Al Merrick and numerous other shapers to R&D new designs that we can bring to the general public. We do have a source for resin transfer molded cored fins. I'd be very interested in working with any designer that brings us ideas that will help move the design evolution forward. One project I have planned is to make a fin root and spline that any foil can be shaped and glassed over. Currently, some of the design elements that make our attachment method as base secure as possible, also make it difficult for fin designers to make proto-types to fit it. Our root has a taper that mates to the taper in our boxes and we mold the side fins at 4 degrees off vertical. I realize that it's much easier to make a Future root. But, we were considering performance as our number one issue and ease of manufacturing the fins was down the list of priorities. Hopefully we can work together in the near future. If you have any ideas you would like to develop further, we'd be happy to enter into a confidentiality agreement to ensure your rights to your intellectual property. John Adrian is our distributor in Australia. If you need anything from us, I'm sure we can arrange it through John or Frosty. Thanks for the discussion, Tom

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Anonymous's picture
blakestah (not verified)

Dave, I would love to see one. I made several prototypes, and asked expert surfers where the fin failed for them in performance, and I did make some non-obvious alterations on what could be considered a simple rotating single fin. The fin has limits built in, and does not have any tail wobble when you go straight and fast. It is literally just like a rigid single fin when paddling and the early phase of making a drop. But it releases at a hard enough angle of attack to generate drive. Anyway, I am certainly interested in what is out there, I did a pretty thorough search of existing IP to ensure that no one had patented what we did, but there are lots of other patented rotating fin designs. And I have yet to actually see any implementations other than my own (but Herb is helping me with that). I am quite sure mine can be adapted to a three fin design, although as yet I am unsure there is a real performance advantage to that. http://www.blakestah.com/fins/

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Anonymous's picture
Herb Spitzer (not verified)

........Got the Waltie boxed up w/ stickers and an old business card,but no instructions,I'll keep looking for them today. ...........Try the SCs and MVG I'm sending you as well,Thanks and I'll let you know whats/hows on you fin system.I plan on building a 6'-? round tail like the Bradshaws that Buttons rode in the late 70s.........of course with some minor updates.Herb

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Anonymous's picture
blakestah (not verified)

I'm sending you a little design guide. But, I am sure you will build whatever you think is best. It is easy to look at the rotating single and think "single fin hull", and you end up with soft rails and rolled vee in the tail that totally screw the actions of the fin up. I recommend a flat tail, rounded pin (or squash or squared off), down rails in back, and enough rocker in the rear for a thruster. The directional control is strongly provided by the fin. The hull from the fin forward can be vee or concave or double, they will all work with different ride characteristics. The fin will re-direct water flow across different points in the tail, and this works best with a flat tail (not to mention flat tails are the fastest). Hope you enjoy it, look forward to hearing about it. http://www.blakestah.com/fins/

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Anonymous's picture
steve (not verified)

Hi There, I would like to know more about your fin system - how much are they? it looks great! I own a business manufacturing specialty surf gear and other composite liesure sports equipment and this looks like a great product - please tell me more! Do you have any testimonials? do you ship to australia? do you need an australian distributor? cheers, steve eagle

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Anonymous's picture
blakestah (not verified)

This is mostly covered at the link below. Currently, any US shaper that does a reasonable volume can have a sample for testing. To anyone else $75/unit, which includes a fin and finbox. There are about a dozen units out for testing, the first "outside" testimonials should come in the next few weeks. We did quite a bit of testing here before sending them to others, the summary of the expert rider results is on the web page below. I am not shipping to Australia yet, I expect to initiate this with the next production round. For any further questions that relate to sales/distribution, email is best, email blakestah AT blakestah DOT com. http://www.blakestah.com/fins/

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Natedanger's picture
Joined: 10/06/2017
Word!
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