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
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.
.........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
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.
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/
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.....
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.
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/
"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/
.......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