So basically if you get up and walk up to the trim spot on your board, the sidebites are merely creating drag, and no other benefits?
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BTW saw some Roy vids recently (Squidtail and another one) where he’s using big thick double-foiled non-toed vertical fins on a twin and single (with cans) and looks to be getting some really fast trim speeds on a high line, not just weight-speed off the drop. I was impressed. He actually did catch a guy from way back and the guy kicked out. Those crazy newfangled vertical fins are the way to go Roy. (I know he’ll be here soon)
I agree Jank. Roy’s vid was pretty cool. Man he caught that guy from way back too? Here is my latest on the vertical fin theory.
I have had a blast on this so far. Super short arcs in turns.
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Any additional benefits, such as drive and turnability, are just bonuses. Please note that much of those add’l bennies came with multiple fin steups, where those extra fins are NOT parallel to the stringer.
The stringer line is a red herring, it’s the angle between the water flow and the fin (or fins) which counts, and the direction of the water flow is influenced by the angle of the rail, NOT the stringer. Singlefins and fins set fore and aft can create plenty of drive, I think that the myth of no drive from fore and aft fins should be laid to rest. 
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…is real problematic for me.
Thats because youre really Roy Stewart.
And you seem to have lots of problems with lots of things,
especially things related to surfing.
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Quote:…is real problematic for me.
Thats because youre really Roy Stewart.
And you seem to have lots of problems with lots of things,
especially things related to surfing.
If Janklow is Roy Stewart then you must be Bill Thrailkill 
(That’s a wink)
Seriously though surely the mods can confirm via ISP addresses that Janklow’s his own man ?
A pity that you have chosen to say that it was such a nice thread
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I have had a blast on this so far. Super short arcs in turns.
How sensitive is it to fore-aft weight placement?
Whenever I used very upright-rake fins I found turning was exceptional IF and only IF my weight was placed JUST RIGHT.
More rake increased the size of the sweet spot. Curious if your impressions are the same.
…ZenSlider ,
my observations and opinions for this issue are based on shortboards; so you dont walk to the trim spot
as you can do (I suppose that you refer) in a 2+1 longboard
I think the sidebites are there mainly for holding because you ve got a hard rail on tail; if not the board will tail slide or get out of control
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Here is my latest on the vertical fin theory.
I have had a blast on this so far. Super short arcs in turns.
Looks neat, here’s our latest verticalish fin thingy:
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Quote:I have had a blast on this so far. Super short arcs in turns.
How sensitive is it to fore-aft weight placement?
Whenever I used very upright-rake fins I found turning was exceptional IF and only IF my weight was placed JUST RIGHT.
More rake increased the size of the sweet spot. Curious if your impressions are the same.
Hard to tell from the pic, but we blunted the front and used a pretty thick foil. It seems to work very much like the winged keel…but shorter arcs in cutbacks and off the tops. I always found winged keels to really come alive in turns, but this one seems bit quicker. This is our protype. We also have a shorter one that looks more like a real spitfire wing. It’s with a test rider at the moment. I wanted a fin not so sensitive to rocker as the winged keel. I am riding it on a zap outline so it’s mostly tail driven. Will try it on a double ender and a longboard and give you more feedback.
Brilliant!
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swied,
Exactly! Rocking and pumping a sailboat is refered to a kinetics. If you time the rocking and pumping correctly at hull speed in waves you can break onto a plane at a lower windspeed than normal as well. And, like you said you need to time the angle of the rudder with the rock to get your forward momentum when there’s no wind to get you to the dock. If you’ll notice it’s in the concave direction of the roll. That’s the cupping I’m talking about. But, you wouldn’t push that much rudder in when you’re flat water planing because you have all the wind speed you need. That’s exactly why convex 80/20 style fins work best when you’re controlling all the power you could possibly want. They minimize leading and trailing edge turbulence while redirecting flow.
On another note: toe does have a lot to do with control. Cant is much more subtle. But, toe is pretty noticable. Take a look at your own avatar. How much more engaged do you think you’re backhand fin is than your front side fin. Pumping is rolling from one fully engaged fin to the other while timing the swing or AOA at the same time. You can gain forward momentum with this timing in lots of different scenarios above dead slow. But, when you are trying to control the amount of power you are dealing with the last thing you want is concave surfaces.
Your logic makes sense to me. I was a little hesitant to make my initial post and step into this debate given my total lack of experience in this area.
I thought of a way to possibly test the drive of a particular fin configuration. Hop on an SUP in a calm swimming pool. Rocking the board back and forth rhythmically should enable you to slowly push the board forward. If you end up going backwards, then you know something is really wrong.
I think I have have been watching too many Myth Busters episodes on TV lately. How would Jamie and Adam confirm this fin thrusting myth?
I put a thruster in the pool and it just sat there, doing nothing…just floated there…
No drive…nothing…
I was a bit disappointed…
But then I put the pump on all hell broke loose!!!
I put it nose first towards the jets…
It moved towards the jet source…
Turned the pump off…
Nothing again…
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I think I have have been watching too many Myth Busters episodes on TV lately. How would Jamie and Adam confirm this fin thrusting myth?
On my rotating single fins, you could get thrust on a longboard. Easily. The toe-in was larger, 4-5 degrees, and the fin larger.
On a shortboard it was harder to feel, with less toe-in angle. But on a short enough board (under 6’2" or so), it was not so tough. The feel was the same and the percept of acceleration towards the nose when turning was pronounced.
I have little to no trust in the surfing perceptions of people who doubt or cannot feel this. It is an intrinsic part of surfing a thruster, and critical to the surfing performance of every professional surfer.
I’m not saying if you don’t feel this you don’t count, but you should wonder what you are missing, because the perception of thrust is very real.
Dave, I understand what you’re talking about, I’ve experienced it, done it, do it, etc, but for the sake of explaining it…you didn’t in your post… under what conditions are you talking about? Why use the esoteric term?
You’re talking about pushing off the flat side of the rail fin face and feeling enhanced drive off bigger faces, right? And mechanical advantage coming from toed-in fins, owing to the downward angle of trim and relative AOA, right?
Since you brought them up, have you gotten any interest from any pros? Has Dan Malloy tried them, for instance? He seems pretty open-minded.
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Dave, I understand what you're talking about, I've experienced it, done it, do it, etc, but for the sake of explaining it...you didn't in your post... under what conditions are you talking about? Why use the esoteric term?You’re talking about pushing off the flat side of the rail fin face and feeling enhanced drive off bigger faces, right? And mechanical advantage coming from toed-in fins, owing to the downward angle of trim and relative AOA, right?
Since you brought them up, have you gotten any interest from any pros? Has Dan Malloy tried them, for instance? He seems pretty open-minded.
As has been pointed out, the thrust in thruster is analogous to a sailboat tacking into the wind. The wind crossed the centerline to hit the sail. It is re-directed towards the rear of the board, but at a slight angle. This angle between keel and sail lets the sail generate propulsion forces.
On a surfboard, the water hits the inside face of the inside rail fin. The forces transferred to the fin are normally referred to as drag and lift. But you can “map” them into forces towards the nose (or tail), and forces towards the rail.
With the rail fin toed in, and water hitting its inside face, there will be a force towards the nose (ie: a propulsion force) and a force towards the rail (ie: a holding force). The propulsion force is the thrust in thruster. You cannot create a propulsive force (where propulsion is referenced to the stringer line) with a fin that lacks toe-in anymore than you can sail into the wind with the sail parallel to the keel.
This thrust force is absolutely critical to modern shortboard function in competition. It depends on board length, bottom contour, rocker, and having the fin separation appropriate both fore-aft, in toe-in, and having the rail fin the right distance from the rail (roughly 1.125 inches).
I had my SurfTrux evaluated by several pros very early in prototype testing, and their feedback was valuable. The feedback will mount with time, there are roughly a dozen Swaylockers with them in hand now…it would be quite easy to get pros to evaluate them if pros were interested…but if you just send something to someone in the industry there is roughly a 99% chance it will simply sit on their shelf.
Hi folks, I’d just like to say thankyou to all of you for the contributions. Its really been wonderful watching the thread grow with so much well considered debate. I’m really impressed with the depth of knowledge held amongst the group, I’ll have to re-read these posts many times. I’m intrigued by the amount of debate in this area, please continue. Steps on the path…
Much thanks and happy waves this Easter,
LionFische.
My take:
I understand what’s accurate about it, but the sail analogy is a bad one. Also superfluous. If you can’t understand this, you just can’t understand surfboards: FACT: An appropriate rail ridden correctly without a fin can give purchase enough for trim, and with gravity, those two factors produce down-the-line progress well, if the rider is able to surf the rail well.
Add a rail fin to this picture and what you have is a vertical control surface that will stabilize the rail in its track from the rear, thus enhance that rail’s purchase and moderate its release very effectively, enough so that you can push off or release the rail much more effectively and stably, and owing to its semi-vertical foil and flat face, you can push and arc off the fin itself to some extent; the ability to do any of that owes much to its mounting angles (if you don’t have cant, your ability to push off it is reduced effectively by every degree of lean angle) but much more to its position in relation to the rail next to it (and that curve or line)—the fin also adds a measure of passive drive.
Given the downward component of trim toward the fall line, a toed-in fin gives a more effective AOA to pump against and arc off, in other words, toe will often allow an aggressive rider to use the AOA better, relative to his desired trajectories–that is, turn-in is easier and in relation to a center fin mounted at an opposing angle, that is, straight; the trade-off being two toed-in fins in opposing angles will produce resistance and significant drag in straight trim.
Have multi-fin boards always had toe-in? Answer’s no, isn’t it? Did they make any progress down the line before they did? Yes they did. So toe-in is not physically required to produce drive (down the line motion)
The stringer relationship to fin toe isn’t the thing. Brother Roy is correct. It’s relative to the curve(s) or line of the releasing rail and any rearward fins. The stringer is a line. Planes are the thing.
2 cents worth from the Flatsville peanut gallery
…all these theories about multi fins creating super propulsions are not super exactly…
in my exp and is my opinion that a finless board is faster but out control too; so you need to put some stuff to hold and to have a direction that you require; the name is fin or fins.
depends on the TYPE of shape the type and how many fins you put there.
for me the last 1/3 of the outline combined with the rocker and type of rail there is the key
like you say, the side fin work to put control (hold and direction, to not slide) and to serve a faster or radical surfer but not for a rookie or not so exp one.
the faster boards (shortboards) (that they have intrinsic speed) are/were those who less drag like one with a single fin an stabilizer in line and a bonzer (that s is like a single fin, but with “help” for some tight arcs)
so, I ride with minimum pumping (but keeping the board always in movement. This is crucial for ALL the modern shortboards) and obtain the SAME speed that the guys for ex in thrusters that need to pump more…
so in my opinion the fins mainly are for holding and prevent tailslides in radical bottom turns, etc
then comes alive the impulse factor; but in second for me.
1. To stabilise a board and hold it in a wave.
2. To allow control of a board.
3. To create drive.
1 and 2 are a given. As far as drive, I certainly can’t explain why, but will relate my experiences and let you decide.
First, the boards… Mainly I shape and surf 9-0 to 9-2 thruster longboards. I use O’fishl carbon thrusters, usually the SS (4.5 inch center and 4.75 inch sides, or more often the TC (4.5") all three. The toe in is what I consider a standard practice set-up, pointing the fins in to meet approximately 2" in front of the nose. On my boards the toe in is set at 3/16". I use the 4 degree cant but combined with the V the cant runs around 6 degree. I’ve tried 8 degree cant plus V but didn’t like the feel. It just didn’t turn or drive to my satisfaction. I put V bottoms and various sizes of double channels in the last third of board.
Drive-- to me --is the amount of resistance I get in a hard bottom turn. In other words, my board will try to gain speed and fly down the line rather than slow down and turn hard. Sometimes I’ll have a board that makes large arching turns at incredible speed with my SS fins. If I then drop in a smaller set (TC), the board’s drive drops and the manuverablity increases greatly. It is amazing what a 1/4" change will make. So, depending on the waves, I decided whether pure speed is in order or ripping is the call.
Also, with my V bottoms, I have found that by adding the double channel in the rear 1/3, that I get more drive out of my boards when it comes time to pump for speed. Why, I don’t know. But it works. So for me, the best combination is toe in 3/16", 4 degree cant, V bottom, double channel. Works every time.
I won’t get into single fins for now, but my experience is limited anyway.
Aloha
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in my exp and is my opinion that a finless board is faster but out control too; so you need to put some stuff to hold and to have a direction that you require; the name is fin or fins.
Underwater fins have a better lift/drag ratio potential than planing bottoms do, so finned boards can in principle be faster than finless boards
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the faster boards (shortboards) (that they have intrinsic speed)
Shortboards are not necessarily faster and are in many cases slower than longer boards Shorter boards do not have ‘intrinsic’ speed, they use the same physical principles as longer boards . .