Stall & Wash-out

General Discussion
1

To the experts:

Boards and fins stall and wash-out.

On any board if you move your weight back and lift the nose the board will stall because this reduces trim speed, however there’s a thing called fin stall too.

Rail fins that are to big tend to create this feeling when the board is triming in a straight line. The will even make a board track back and forth from rail to rail because the alternately over power the board. But there’s more to the stalling reference than this.

Details please ~ ?

When a board washes out it seems to me we’re talking about its inability to hold a line, side slipping or skating are very closely related to this term. Fins wash out too. Sometimes when you try and drive off them you just dont get any punch, like when a single is too far forward for the size of the waves you’re riding.

Clarifications ~ ?

Thanx ~ Gone Surfin’, Rich

2

You know what Roy ~ You think you know a hell of a lot more than you do. So go pound sand!

3

Even after surfing and making surfboards for 20 years, and windsurfing and helping design fins, setups, materials, and such for 25 years, it’s still a mystery of combinations and slight nuances.

Certainly, introducing air bubbles to the equation causes some fins to just loose grip entirely, whether single tail or side. Imperfect foils magnify the problem.

Smooth riding, keeping the rail set and well controlled, seems to alleviate the spinout/cavitation somewhat. Bumpy waters or jerky surfers tend to increase the chances of spinout/cavitation.

I used to ride lots of twin fins. Can’t say side fin size is a culprit. I’ve used mainly 6" tall side fins, with about 5" chord. Sometimes, have gone up to 8" tall side fins, with no problems.

My 8’6" Pipe gun had two 6" tall sidefins, with a tail width around 11". Was fine and loose.

I think a combination of wide tail, harder rails, concaves at the back foot, bumpy waters, rider herky jerky, lightweight boards, all contribute in some part to the spinout/cavitation of fins.

One of the reasons that Mav guns wander towards quad fins.

4

Thanks Lee,

Very much the voice of reason and experience here. It’s good to get some perspective on the high performance edge of things, which Mavs certainly is.

Certainly the more air there is in the water the harder it is to track. What I’m getting at is how these terms are defined and pinning down exactly what we’re talking about.

I come here to learn and share what I found will work or a common surfboard. There are some very uncommon approaches that may be valid and I’m up for looking at them. Some mine are consider uncommon no down.

I want to be perfectly clear that I only come here with a few modest humble opinions.

When I know I don’t know then I know.

I hope Blakestah, Rob, Mark, Dale and few of the grand minds here at Swaylocks can help get the terminology straight.

Mahalo, Rich

5

Stall is defined based on lift:drag curves.

As you increase the angle of attack, or angle of the fin relative to the water, the lift increases up to the maximum lift angle. This is also the stall angle, further increases in angle of attack decrease lift. Drag is always increasing with angle of attack, and tends to increase sharply above the stall angle.

Lift angle tends to correspond to the angle at which flow attachment on the trailing edge breaks, and the low pressure side of the foil has a disturbed mess behind it.

Lift is defined as the force perpendicular to the water flow.

6

Roy,

You don’t know what you’re talking about.

IMHO you are not an expert. You are no bigger than anyone else and your scope in painfully small.

I’m not being abusive I’m stating fact.

You live in a tunnel and it stinks.

If you think this is abusive don’t get me started because you’ll be in for way more than you can handle.

Yes this is a public forum. I don’t set myself up as anything but what I am, that is, one who is attempting to learn about surfboard performance in my own humble fashion. I share what I think works and what other people tell me works. I ask advice from the masters. There are many here in Santa Cruz. I am amoung the least of them but I do have so sterling reports on some of my creations. Frankly I know your tunnel fin is crap on a modern high performance surfboard, so don’t bother me with it because by doing so you reveal how completely self possessed and entirely intrusive you are. Such a posture has no place in this discussion of what Stall and Wash out is.

So post away your stuff is nonsense and jibber jabber in the humble opinion I’m entitled to.

I will not address any of your half back statements about theory.

Rich

7

Blakestah,

Ah, the soothing sound of reason! How refreshing to hear definitions and clear reasoning about what the effect of stall and wash-out are.

So what we try to create is a fin that will give the best lift without washing out. As the angle of attack increases drag increases and as washout increase drag increases, or am I wrong?

Fin perfromance is best when lift is maximized and drag is minimized. This seems the correct way of saying things to me. Different foils on a single fin will create a different amount of lift and create more sensitivity turning or be more stable as speed increases. Fins that are more speed sensitive make for a more exciting surfing experience IMHO. That’s what I try to make without sacrificing stability as speed increases. It’s tricky bussiness, just like the terminology but

When drag is greater than lift, if we can equate things this way, we then have what we can term as stall.

As lift is compromised for whatever reasons, we can say the fins wash-out. And they drag as the do so.

It would seem we could say washing out is the process of loosing lift. Producing power when turning, the ability to drive, seems what lift is about.

I’m trying to get things straight so I can discuss fin performance with a better use of the terminology that discribes the way they affect board performance.

Thanks again Blakestah –

Rich,

P.S. It’s all in the foil.

8

You might also drop in on the finmakers of windsurf boards. They are planing vehicles with rider side pressure, so it’s sorta applicable.

Seems hi aspect, short chord with some NAACA foils (obviously, I misspelled again) are the key to anti cavitation/spinout/stall, and any knick, scratch, or flat spots from grinding on the bottom induces the above. Such are the best for low drag, high lift foils.

Some really knowledgeable theory peeps are involved in high end finmaking for windsurf boards, with boogie of C-3 fins (gaastra forums), one of the leading debaters who really seem to know what’s going on underwater.

For sure, traditional wave fins, with say, a 9" height and 6" base, are one of the LEAST efficient shapes availible.

Pure blades are the most efficient, for lift vs low drag.

Lotsa theory, but almost all fast fins are tall and skinny, like the cutaway tris on your own board. BTW, how are they working? Are they stressfractured yet?

Since windsurf fins are longer, regular fiberglass have almost dropped off the planet, unless used with wave fins shorter than 8". G-10 was the choice 10 years ago, but durability problems surfaced with longer and narrower fins.

Carbon composites, glassed over foam cores, with controlled flex, seem to be state of the art…and extremely expensive and fragile.

9

Seriously,I ride a thruster to avoid the problems associated

with the tunnel fin.

Alternatively, I ride a thruster to avoid the problems of

twin and single fins.

No design is perfect, some much less perfect than others.

10

You are smart, KISS.

However, other’s like to explore the edges of reality, push the edges of design, and go where no man has gone!

11

Back in the early to mid 70’s, I was making foam and glass fins. I make them with exagerated foils, about 3/4" to an inch thick with a very pronounced cord. There was no loss of speed from the thickness, but,…when you picked up speed, the pressure gradiant would change from side to side and cause the tail to occilate from side to side. One of my riders on Maui said it was very unnerving to be slotted at Honolua, going into the bowl and have your tail start doing the twist. gotta lay off the acid

12

I remember those, have used a few production copies made of lexan…or clear polycarbonate. They worked great, at Pedro, Bolinas, Santa Cruz.

They were weird at Ocean Beach and Deadmans, so we put them in the back burner, another good idea with limited applications.

They certainly allowed for very wide turning directions, holding power, slipperyness.

We thought Lexan/polycarbonate was just a lousy fin material for big, fast waves. What did we know?

13

I am unfamiliar with the term washout in these terms.

In aero literature, wash refers to flow around the foil.

Downwash comes from induced drag. This is the problematic current that runs around the tip of the fin, letting high pressure side go to the low pressure side.

Washout is a way to deal with tip stall. If the tips stall first, wings can be hard to control. So, on a wing that would otherwise stall the tip before the base, the tip can be turned to a lesser angle of attack. On a thruster fin, this may occur if the tip is toed in MORE than the base. The additional twist to re-angle the tip is called washout. Whether it is desirable depends on whether tip stall is problematic.

There was a really good video demonstration of thruster fin stall from Teahupoo. Someone (Lopez, maybe) was making a really late drop, and had angled his board considerably. His fins stalled - both stalled, and he adjusted so only the rear fin was in stall, and then took a harder line again - obviously tracking across the wave as hard as possible without stalling both fins. He went into a complete stall at least twice, pulled out of it near the bottom, mashed a bottom turn, and got sickly pitted. I think on video I saw it in slow-mo, quite impressive.

I am not clear what your use of washout means, though.

14

Guess I’m no engineer (whom I always make fun of).

I can never relate the terminology with the symptoms, and consider all the stall/washout/cavitation/spinouts with a …BAD BERRIES!

Just a simpleton here, sorry.

I DO know a high aspect foil, foiled with care, tenderness, and a knowledge of NACA profiles tends to hold in most situations, speeds, and sideloads.

15

Hi Halcyon

I havnt heard the expression washout used in relation to fins having lessening grip

I dont know about any one else but I would of called that drift (as in away from the direction of the turn)

I say this properly because, as i posted on the other fin thread a while back, I talked about fin washout which related to the twist in a wing (aviation) or fin.

As for thruster toe in drag I do belive that there is some outward flow to wards the rails on a board so that fins with no toe in do cause drag

Its much the same on a boat if you have twin rudders they have to have some toe in or you get drag.

As some of the water displaced by the boat body migrates to the sides

regards Mike

16

Roy,

All designs have negatives.

There is no perfect design, as any design

is a compromise of alternatives…

…‘period’( that period part is a famous quote)

As to touting your products I suggest you come

to the racetrack with a Sports Car instead of a Truck

to demonstrate what you consider superior design and

implementation.

Else how can you blame anyone for an impact that doesnt

meet with your approval.

Didnt’ I spy on your website a tunnel board that had

fins that looked like they were cut out with tin-snips or

something only slightly more elegant.

Joel Tudor would hard be pressed to put your

equiptment through comparitive and competitive trials.

Frankly, I dont think I’ve heard you relate any negatives

of the tunnel fin…makes one wonder??

17

Lee DD,

I’ll check out the forum. You refer to. I’m sure there are lots to learn there. I agree with you completely about maximizing fin performance when it comes to templating and construction. When I make singles over 8.5" or so that have much cord length for common surfboards, (Mostly longboards) I like to use an epoxy laminated spine in a high density foam sandwich and laminate an epoxy shell over the rough foil. It makes an extremely light fin that is very powerful because the three sheer walls work together to make the fin very strong. Fins that float are good.

I haven’t had any of my polyester fins stress crack unless they were bounced off a rock or the bottom For fins under 8’0" and tow-in singles that need to be high aspect stiff and very strong Carbon/Fiberglass/Epoxy is the ticket. The combination of these stacked properly makes a tremendous fin. For it’s thickness it is very, very strong. If foiling for flex is in the picture the memory recovery curve is much steeper for this composite than Polyester. It’s like the difference between an old Fiberglass fishing rod and a new graphite rod. Fisherman that I am the crossover seems obvious though somewhat time consuming to produce.

I’ve fussed around with G-10 and the stuff is hard to work and very heavy. I prefer to make my own fin stock. I think it’s possible to make a better product this way.

Jim,

I know what you mean about extra thick fins. When the vertical cord is held forward and the fins are of an exaggerated thickness they don’t track well as speed increases. It makes for a very unwieldy feeling when you really get the board going. A top surfer I made a couple of fins like this for called them twitchy.

Mahalo, Rich

18

Roy, reread your posts and you’ll see that everyone can say what he wants here…

Anyway, as HalSose said before, it seems like you have the only perfect fin design in the world, so reconsider it’s price, 50 bucks is really cheap for some PERFECT fin set up plans.

Reading you i can see that you’ll be the next Simon Anderson, is just a matter of time. Be patient.

Good waves!

19

Hi Roy

Too bad about the weather hay,at least there have been waves on the east coast for the last couple of weekends it makes a nice change from the west coast

Fins, toe in I find the best for me is 2 degrees relitive to the stringer on a board thats 6’4" with a tail of 14 1/4" and me at 82kgs, at average wave speeds down the line the back of the board is down in the water about 1 1/2"to nearly 2" thats still quite a lot of water being displaced out the sides

On the boat its 3.8 degress but only really at low speeds are both rudders fully in the water, at any speed the apparent wind comes forward the boat heels waterplan form changes shape and the weather rudder only has the tip in the water,which is doing nothing but draging

If I had been smarter I could have made them kick us and got the weather one clear of the water earlier

The little fin boxs that I make for myself were at the begining just so I could play with toe in on the same board on the same day and really feel the differences that it makes

Now the same little boxs are leading me to try lots of other ideas,as different shape and camber fins seem to not all work best at one toe in angle

Regards Mike

20

Blakestah is making a good start, but honestly I’ve heard a bunch of retired guys with model airplanes use more accurate terminology than most of the discussions I read here. Here’s a bit of stuff borrowed from basic aerodynamics, skip it if you wish:

Foils are devices that provide reactive forces when in motion relative to their surrounding fluid; they can be accurately described by their chord, camber, thickness, and thickness distribution.

The chord of a foil is the straight line joining the ends of the mean camber line, i.e. from the leading edge to the trailing edge.

In a symmetric foil, the distance from the chord line to upper surface is always equal to the distance to the lower surface. In a cambered foil, this is not the case.

The mean line is equidistant from the upper and lower surfaces of a foil.

Camber is the maximum distance between the mean line and the chord line. If the maximum distance between the chord line and the mean line is 4% of the length of the chord, the foil has a 4% camber.

Camber is a straight line on symmetrical foils and a curve on asymetrical foils. (that means Chord and Camber are different on asymmetrical fins)

Thickness is defined a a percent of Chord.

Angle of Attack is the angle between the foil’s chord and the relative wind (or relative water for a fin)

(there are several ways to define AOA if you want to get really technical).

Path Velocity is the speed and direction of the foil, which is the opposite of (and equal to) the relative wind/water.

the Mean Camber Line is exaggerated in order to show the chord clearly.

As the angle of attack of a foil is increased, its coefficient of lift increases - up to a point. If the angle of attack is increased further, the rate of increase of the coefficient of lift is less, until finally it starts to actually decrease. The onset of a stall is the point at which the flow over the foil ceases to be a well-behaved laminar flow and the foil starts to lose lift. A foil stalls at a predetermined angle of attack.

parasitic drag, is resistance of the foil to the water through which it moves. Parasitic drag increases with the square of the speed.

induced drag is related to the foil’s production of lift. Net lift is produced at right angles to the chord of the wing. Since there must be a positive angle of attack at low speed to produce lift, there is a component of the total hydrodynamic force which resolves to a vector in the drag direction. At low speed and high angles of attack, induced drag increases and becomes a large factor.

washout is a defined term related to “twist” in the foil; washout is a twist that places the leading edge higher than the trailing edge as you move from root to tip

twist is the relative angle of attack at the root and tip of a foil.

Washout is more important in aerodynamics than surfboard fins because that airplanes have critical control surfaces located near the tip of the wing. These ailerons allow pilots to turn the plane and pull out of spins. Fins have no such control surfaces, thus tip stall is not so critical. (Plus airplanes tend to fall out of the sky when they stall, much more dangerous than stalling a fin – except perhaps at Teeahapo or however you spell it.)

That being said, not all parts of the fin generate lift equally; and its probably still better to have fins stall gradually rather than all at once, because that increases control.

There. Enough insomniac terminology…