Thick fins vs. Thin fins

General Discussion
61

Blakestah,

Thanks for doing the math for me everyone. Okay good, 12.something cc’s. Lets round it to 10cc for the sake of discussion. That’s 10cc in say a 4" wide fin right? Can we safely agree that this 4"w fin will always be 4" as it displaces 10cc of water? Right? Let’s say the difference between the thick and the thin fin is 2 cc. Also, before I forget 1cc = 1 ml for our fluid conversion friends.

Now ride your board 100 yards with one of those 10cc fins. Sorry for mixing my measurements.

That’s 36 inches in a yard times 100 yards for 3600 inches divided by 4 inches for the size of the fin which is a fixed number and you get what, 900? That’s 900 times 10 cc volume of water that your fin has displaced. Or stated differently 9000 cc’s of water that fin has had to push out of the way and move around it. That is only if you can surf in a perfectly straight line, too. How much does 90 liters of ocean water weigh? Someone has the answer, till then, this will have to do, a 2 liter bottle of Coke weights about 5 lbs. So 1/5th of if for the 2cc is still a significant difference. On a thruster that’s x 3 or 27000/20 for the 2cc difference or 13.5 liters of water difference between a set of three 10cc volume fins and a set of three 12 cc volume fins. Is that right? 33.75 lbs of Coke? If so it’s a lot of Coke or water, and a lot of weight to be pushing around.

Remember that scene in the movie Without Limits where track coach Bill Bowerman describes to Pre how taking a 1/4 oz off the weight of a running shoe over the distance of the race lowers the total amt of weight a runner lifts overall by a huge amt? Well, if he was smart enough to found NIKE maybe that is the physics lesson we should be applying here, before we write off a couple cc’s of water as insignificant. Great movie too. I followed Pre’s career and I remember where I was when I read about his death. That sucked. But look at NIKE.

It’s not long before we are talking about dragging serious poundage. Especially paddling all day.

Volume is important. How we use it is the key.

Don’t bust me on the math, because I can’t even add. But check the numbers and if they need work, which they always do, please by all means.

Anyone know how to convert fin data to horsepower? Because horsepower required on a working system is horsepower delivered. My brother and I went through all this years ago. It was fun, but I’ve forgotten it and the emails are long gone. I think the number was relatively small like less than a quarter. Don’t quote me though. But lift converts to horsepower realtively easily. This is past my math ability.

I have another formula my brother scribbled on a napkin at dinner last January, but I have to find it first. It was good.

Mark

62

Hey Tubedog,

1 cubic inch = 16.387064 cubic centimeters

An object 1/8" x 3" x 2" =.75 cubic inches or 12.29 cc.

Just so you know how Bagman got there.

Good waves, Rich

63

http://www.mh-aerotools.de/airfoils/index.htm

Good theory on low reynolds number foils, includes foil sections and a great Java applet.

64

Halcyon,

Many people have remarked about the shape and efficiency of a wing with an elliptical planform, particularly with regard to the Spitfire fighter aircraft.

[ For the record this fin has it’s shape taken from and outline that was proven long ago to have lowest drag coeffienct of any wing shape. Sir Reginald Mitchell used it on his Marine Spitfire. Argueably the sweetest flying prop driven airplane every to mount the sky. Watch a movie of one in the airplane sometime. She is a magic! Have a look at the relative thickness of the wings. ]

What a lot of people don’t appear to know is that the Spitfire wing shape was designed before the theory proving its optimum low drag characteristics was widely published by the famous aerodynamicist Prandtl (who worked in Germany).

According to a quote from Aerodynamics for Engineering Students, 4th edition, p315:

" Probably the most famous elliptically shaped wing belongs to the Supermarine Spitfire. It would be pleasing to note that the wing shape was chosen with due regard being paid to aerodynamic theory. Unfortunately, it was extremely doubtful whether the Spitfires Chief Designer, R.D. Mitchell was even aware of Prandtl’s theory. In fact, the elliptical wing was a logical way to to meet the structural demands arising from the requirement that four big machine guns be housed in the wings. The elliptic shape allowed the wings to be as thin as possible.

Thus the true aerodynamic benefits were rather more indirect than wing theory would suggest. Also the elliptic shape gave rise to considerable manufacturing problems, greatly reducing the rate at which the aircraft could be made. For this reason the Spitfires elliptical wing was probably not a good engineering solution when all the relevant factors were taken into account. "

Sadly, the Spitfire Chief Designer designer, never saw his plane fly in combat because he died in 1937.

Note: Another urban legend bites the dust.

65

Tom,

The keel on your yatch has a leading edge fillet at the root of the base.

It is known that such a leading edge fillet at the junction between the hull and appendage miniimises or eliminates interference drag.

The fillet suppresses the formation of horseshoe vortices which causes this drag.

So Tom, if the filleting is good enough for your yatch then are we going to see Red-X fins and bases equipped with root fillets.

Can I suggest you make the leading bulb tip more rounded to minimise the possibility of tip separation effects in crossflows.

66

It’s not my keel. It’s the keel of the boat I’m racing on. The funny part is, the boat was just recently purchased by the daughter and son-in-law of the man who built our boat some 25 years ago.

But, in answer to your question. It’s something that we have been considering. But, testing always comes first. And, I have not had a set of proto-types made yet to test that feature.

You might want to make your tip recommendations to Allan Andrews. His firm designed the new keel.

67

Tom

It brings back memories of George Downing’s bong fin which came and went although I’m not sure exactly whatthe problems were.

My brother had one on an old 80’s Get Wet thruster that kind of looked like a fat flyer ala no re-curved tail like Bert’s version. He said it was one of the best tube riding boards he ever had. I think it was like 5’11’ or 6’0", the old one foot on the nose and one foot one the tail type of board.

Anyone know why the design drifted away?

Cheyne’s/Ben’s wing design seems to have lasted alot longer.

Was it the design of the base?

And for everyone else…

Anyway like DanB another stoopid and aged design grem question/observation, but here it goes…

eventhough mankind has been doing it for eons, does it ever make sense to take a single component of a very complex organism like an appendage off a living creature and think you can duplicate what it “actually” is doing when it’s attached to an inanimate structure?

Seems to me that these appendages of fowl, fish or mammal are working in cooperation with what’s going on which the rest of the living body. And that is being affected by what the paticular bone structure, profile design , weight to size and especially the muscle and skin components are doing in the first place to support the activity involving these appendages(fins/arms, legs etc).

Knowing how engineers, mathmeticians and physicists think… We usually believe we can resolve the world around us in a single equation or a value in a lookup table in some reference manual somewhere…

Like an old brilliant professor of physical oceanography told me back in the 70’s, “calculate what’s going on in a single molecule of ocean water at any depth and you’ll figure out the ocean”. I can see this methhodology working in inanimate static structures and very large or very small entities but applying the same design concept to a living breathing biomass? I don’t know…

Seems like some type of biologist, behavior physiologist, physical therapist or medical doctor would be better at trying to understand these complex relationships and how they interact with each other…

Some how I don’t think boats and surfboards work exactly how a large fish like an Tuna, Porpoise, Orca or shark do… There’s a huge muscle mass, flex relationship, and skin component being ignored when you just stare at the fin appendage…

The wings on aircraft usually are many times more massive in surface area than the body they are attached to and the tail rudder is usually only for stablization. They also all usually have moving rudders attached and a some big propulsion system attached as well with the exception of gliders which have absolutely huge wings. Parasails, hang gliders and hot air balloons use ribs and thin flexible skins that move in conjuction with the fluid mass(air) they manage. never seem fins on surfboards look like this…

Looking at things in it;s entire entity would maybe get us closer than micro analyzing…

Fat and curvy seems to me is just esoterically more pleasing than hard and thin edged. Lines as they move through space have meaning maybe that’s why they work… cuase they blend into the ethera around them more harmonically… (string theory)

just another grem

68

if we could shrink an orca and enlarge a gold fish so they were the same size …

which would be faster and have more control ??

good fins transfer the riders power , were not just hanging on for the ride , we can make our own speed …

if our fins are thin , we just flap around and go nowhere …

displacement needs to be offset by pressure difference …

the fuller the foil , the lower presure surrounding the surface of the foil …

bernouli’s rule , as the speed increases the pressure decreases …

a full foil operates in a region of lower pressure thus reducing the overall drag , a thin fin operates in higher pressure coz the water doesnt get displaced as far ,so if both fins covered the same distance , the extra water displaced is offset by a region of lower pressure water around the thicker foil …

the biggest problem here is presumption … we presume a thick fin is slower therefore it must be and we look for rational ways of explaining it …

it would be so much easier for me to make thin fins , but i make thick fins because they put magic into my boards …

i did the trial and error first before i learnt why and how via the text books …

when your testing surfboards and fins everyday for a living and find that everytime you put thicker fins on your board it goes faster , when you give boxes of different fins to teamriders and they come back and say "ok i still dont believe it but these fat ones go best "

apologies blakestah …

but i feel to really get a handle on some areas we have to go to extremes …

then work our way back …

i was most impressed with carls finless boards , he went to an extreme and learnt something …

ive found we surf our fins as much as we surf our boards , i would rather increase fin area and decrease board area , we plane on both …

going rail to rail is really going fin to fin …

our fins make up a way bigger percentage of effective surface area in contact with the water when going hard rail to rail power surfing ,

if we only have the back 20% of our board in the water , then calculate what the % of fin area is in comparison to board area in contact …

yep , good fins are what were actually surfing …

time again …

gota go …

regards

BERT

69

And for everyone else…

I’m going to take this and with apologies thread my eply.

Anyway like DanB another stoopid and aged design grem question/observation, but here it goes…

No such thing as a stupiid question today.

eventhough mankind has been doing it for eons, does it ever make sense to take a single component of a very complex organism like an appendage off a living creature and think you can duplicate what it “actually” is doing when it’s attached to an inanimate structure?

Absolutely. The US NAVY thinks so and it funds universities.

That is why we rule the seas. Look at our submarine communicton system. Directly an offshoot of whale research.

The researchers found that whales can talk over thousands of miles. They figures out a way to sort of copy. But whales are still much better communicators. Research continues.

Seems to me that these appendages of fowl, fish or mammal are working in cooperation with what’s going on which the rest of the living body. And that is being affected by what the paticular bone structure, profile design , weight to size and especially the muscle and skin components are doing in the first place to support the activity involving these appendages(fins/arms, legs etc).

Good points. Creatures have evolved to the sizes shapes musculature and type of muscles (fast twitch slow twitch blood supply use of oxygen etc) for a reason. Researchers are just beginning to figure out how creatures like tuna work. First research into how tuna swim was late 1990’s and reported in 2002. This is cutting edge. Google Jennifer Nauen. She knows me. She got samples of my first MVG prototypes 6-7 years ago.

Knowing how engineers, mathmeticians and physicists think… We usually believe we can resolve the world around us in a single equation or a value in a lookup table in some reference manual somewhere…

Like an old brilliant professor of physical oceanography told me back in the 70’s, “calculate what’s going on in a single molecule of ocean water at any depth and you’ll figure out the ocean”. I can see this methhodology working in inanimate static structures and very large or very small entities but applying the same design concept to a living breathing biomass? I don’t know…

Well that’s an over simmpification. My brothe rspent 10 years gettign his computer model simulationof the Gulf Stream to cycle continuously and to zero out. meanwhile commputers got way better so now the research is dated. Adnhe got his PhD just a few years ago. Things move fast but there is so much to learn it seems slow.

Seems like some type of biologist, behavior physiologist, physical therapist or medical doctor would be better at trying to understand these complex relationships and how they interact with each other…

Some how I don’t think boats and surfboards work exactly how a large fish like an Tuna, Porpoise, Orca or shark do… There’s a huge muscle mass, flex relationship, and skin component being ignored when you just stare at the fin appendage…

True. Agreed. But it’s easier to start with nature than not to.

The wings on aircraft usually are many times more massive in surface area than the body they are attached to and the tail rudder is usually only for stablization. They also all usually have moving rudders attached and a some big propulsion system attached as well with the exception of gliders which have absolutely huge wings. Parasails, hang gliders and hot air balloons use ribs and thin flexible skins that move in conjuction with the fluid mass(air) they manage. never seem fins on surfboards look like this…

Probably won’t either. Specilizaton. Key feature of nature too.

Looking at things in it;s entire entity would maybe get us closer than micro analyzing…

Micro and macro. From strings to universes. It’s all fair game.

Fat and curvy seems to me is just esoterically more pleasing than hard and thin edged. Lines as they move through space have meaning maybe that’s why they work… cuase they blend into the ethera around them more harmonically… (string theory)

Einstein said ether was bunk. But what if strings arent strings but 3 dimensional like a plastic bag and we only have math to “see” them as strings? We dont know. Nobody does. That is the motivation.

just another grem

[Smile]

Nana ike Kumu (look to the source)

70

I’m not sure that I like being the posterboy for “stoopid and aged design grem question/observations” :slight_smile:

71

Picture 1. 1/2" thick single fin (heavy). Fiberglass core with flexible urethane. ONLY single fin I saved.

Picture 2. Bobby Owens football fin with tape on edge to fit it in Bahne long box. Last movable medium-thick fin I owned before the thrusters and clusters.

Picture 3. One of the first ads and marketing that would eventually kill the single fin. “Convert your old single fin”. “Turn your surfboard on” and “Do your board a favor”. (Ad used without permission - Surfer Magazine)

The cost and weight factors of laying up three thick fiberglass fins surely had something to do with the focus on thinner fins. The manufacturing techniques of vacuum-bag wood core, pre-preg hollow and foam filled will bring back a thicker fin renaissance, as more young-uns stretch their wings and try different feelings/experience. Force of will and attitude only ads will not cut it anymore.

Another consideration is ADDITIONAL SURFACE AREA of a thicker fin. Which relates to a more CURVED surface. I always wondered why a domed or channeled or bonzer style tail worked. Outie or innie? Does the overall surface area play just as much a part whether it is curved out or in? More water contact with the benefits of a reduced overall outline?

No fins? The reason no fins hasn’t worked so well is you can’t design a RIGID multiple concave or convex surfaced wave riding craft that can utilize the flow of energy and take all the changing variables into account. (see Tom Morey - boogie board) The major reason is - wave face suck. The surface of the water lifts up into the wave face energy hump and you need extreme amounts of the quality - RELEASE. A ufo type surf craft gets its hold from increasing surface area that is in contact with the water. Run a string over the surface of the tail from rail to rail and measure the true width of one of these boards pictured earlier in this thread. You might as well of stuck a small airplane wing on the bottom of the board.

Inspired by nature. What type of fins do fish have and what are their structure? Paddle or rudder (directional fins) would be their arms or pectoral fins. At slower speeds the arms are held out and water is deflected from side to side to initiate turns. At faster speeds these fins tuck in and most of the speedier fish use their dorsal fin as a directional stabilizer with just a nod of their head to redirect body. The tail fins are larger to push through, power forward. It seems that animal fins have a DIFFERENT designs to solve each need. Front view - the larger animals fins taper from the body to tip - thick to thin. Minimal bone structure, some meat for control and a membrane of skin. But they all tuck their arms in at speed.

This part is where I slowed down and took a leisurely look around at nature. The larger the aquatic animal the bigger the bone, hence the more meat and darker opaque skin (colored to absorb the suns energy and heat the meat) needed to efficiently redirect their moving body through the medium which they travel. But the smaller fish just have a clear MEMBRANE of material that does the job. Now we’re getting back to the overall surface area of the fin, but it is related to the laws of nature this time where a smaller creature can get away with less surface area and far less mass cause the effects of gravity are far less and almost nil when you get to bug size. Example; when a mouse falls out of a high building, it will survive the fall cause gravity/weight effects are equal for him falling 1 foot or 100 feet. His weight has little or no acceleration? value compared to the human who’s overall weight value will speed us up to the force of gravity effect and meet the ground with you know what results. How does a bug fly? now there’s an aerodynamic disaster. Big old round body, armored truck filled with cash kinda guy, with some flimsy flight membranes, heck, they aren’t even curved like the requirements for bird feathers cause of the effects of gravity ALLOWS them to just beat that membrane against the air and get up into that upper wind layer and see ya later, I’m wintering in Hawaii, bro.

So then does thickness relate to force applied OR size of animal (overall surface area) OR weight of animal (volume)?

Single fins, of yore, were mimicking the dorsal fin ie; you need forward speed to make them work. The original fish design, then twin-fins, used the toed in (pectoral) fin to create a little more inside fin area, turn around the orange cone, flaps down, and hold on to wave face to initiate turns and build speed by leaning rail to rail (drive and projection). Of course I mean redirection but unless you know the secret, and that is you have to surf constantly rail to rail or you are dragging one (or two) rail fin(s). The thruster cluster just smoothed the jerky 2 fin acceleration process and made vertical surfing work cause you can free-fall with just that hind-fin scratching some water to keep the feets in-place.

You could argue that because the board is lighter, the fin should exert more force, for acceleration purposes. Or cause the sea animals that are our size have some girth to 'em, so should our fins mimic these same qualities? How about the more weighty beings (us) accomplishments? We could use the facts and findings of ship and plane builders to start with. Reams of documents there. Oh darn, most everything uses an engine, of some kind, for acceleration. An olympic speed skater is fast in a straight line, but at start-up you see that sideways pointed, digging in blade, toed-out? but at speed those blades just scratch a little bit out of the straight speed-line to MAINTAIN that built up speed. Is that how we get speed? Hooked into the critical area energy of the breaking wave always sideways scraping? BUT what about the glide? NEWS FLASH - we are going lighter and tuning our twangers.

Can you see what I feel? (string theory?) Throw away the box, you know, the one that we’re supposed to be thinking outside of? That’s just unnecessary surface area pretending to be a luxurious baggage set. Maybe look to the smaller fish and bugs for inspiration. Let your freak flags fly. Tucked in membranes… Hmmm.

This is by no means meant as a redirect. It is only a base coat for your - I’m not so sure I see fins in the future remark, Mark.

daddio - the ultimate gremmie



72

thanks Mark/Bert

And sorry DanB I apologize for any inference… It more what I feel like based on the responses to our questions some times… Hopefully mine have never mine to you never made you fell the question was silly…

Sorry for the grammar/spelling

trying to type something coherent at 4 in the morning before rushing out to fight morning traffic is a challenge for me… But this is a good thread like all the other fin discussions started here…

I thought I’d throw this out for feedback, but why hasn’t anyone actually built some prototype surfboards that have their bottoms covered in pressure sensitive pads and develop the same material wrap to cover the outside of fins as well. Then wire all this up to a data capture box that can be inserted into the top of the said prototype board and test all these design concepts surfing real waves with a real surfer doing stalls, hand drags, cutbacks etc etc the kind of things you can’t duplicate in a wave tank test… I’m sure the technology is out there and maybe some industrious surfing master or doctoral candidate can pony up an RFP to Intel( or another deep pocket) to get some funding to do this… Intel just spent some dough doing that stupid PC in a longboard concept… Seems like everyone else(Solomon, RR, Surftech) is focused on materials and not design This would have much broader scientific benefit… Imagine what we all would learn from all the numbers gathered…

Secondly, has anyone gone out and gathered all the underwater action shots of boards in waves like Don King’s stuff or the Search footage of Curren in Indo and run all that video through those DOD starwars image analyzers to get the math on what happening underwater between the curve of the wave and power of the wave and the interaction of the board, fin and its affect on laminar flow… If so what were the results?

Doing this all by “feel” and in static wave tanks seems so backwards when the technology out today would support a real “in the field” scientific analysis of how boards and fins work. Also looking at things just from above the surface doesn’t seem to be a “real” scientific approach especially with all the development of sensor technology,micro computer horsepower and graphical analysis tools available today.

Isn’t there enough global scientific interest to do the proposal paperwork to get the apprpriate funding from an Intel or Dow Chemical company to complete this type of research?

Just wondering if any of this has been done and why if not why not? Or why no one’s willing to throw the hundreds of thousands or millions of dollars needed to complete the research. It’s a drop in the bucket to a company like DOW chemical or Intel… Just find a closet Surfer on one of their boards…

Or maybe the answer of why not is staring us in the face and we just don’t want to see it or admit it.

That’s why I like chip… I think he get’s it… try everthing and anything but just have fun…

Hey but the scientist still left in me wished someone would do the project right using the best equipment available today…

Again another great thread from Mark and the fin gurus…

gotta go

73

I understood what you meant. I wish that the smilely looked more obvious (but its there at the end). What makes this forum so amazing it the thought and respect people put into their responses.

74

Two links: one old one new.

Sorry for the cut and paste.

First the old:

http://www.blackmagic.com/ses/surf/papers/physicsgrm.html

The new:

http://cetic.swan.ac.uk/surfs/

Bookmark or Favorite these links.

I read this stuff like it’s a homework assignment. It’s good, but it all takes some time to chew, digest and absorb.

I did and I’m still choking.

Point is we will all be doing these guys a service if we try and understand what they know, are learning, and about to teach us. There are some powerful brains getting involved.

I’m not a guru, just a surfer like everyone else. m

75

These were written in 1968, still worth digesting today.

http://www.rodndtube.com/surf/info/Hydrodynamics.html

76

“Example; when a mouse falls out of a high building, it will survive the fall cause gravity/weight effects are equal for him falling 1 foot or 100 feet. His weight has little or no acceleration?”

Good one Daddio,

I chose this because it points directly to one of the mysteries of flight. But the answer was simpler than Bell Labs or Exxon Labs or any of the research engineers or physicists who puzzled over it at dinner parties in the late 60’s early 70’s thought. Now every elementary school kid can understand. Including me.

How do Bees fly?

They have no aerodynamic design, so theoretically according to then current theory, they should not be able to fly. But the answer is that air is to bees like water is to us, a viscous liquid. Their flying is kind of like our treading water. But that grotesquely understates their ability. How can they fly so fast through air if it’s as thick as water to them? And they are so fragile. Totally amazing. Talk about thin wings…

Remember basic physics: Drop a mouse a bee a feather and a boulder in a perfect vacuum and which will fall faster?" M

77

Remember basic physics: Drop a mouse a bee a feather and a boulder in a perfect vacuum and which will fall faster?" M

In a perfect vacuum, wouldn’t all fins work the same?

78

In a perfect vacuum, wouldn’t all fins work the same?

Yes and no. Explaination:

Actually in a vacuum you don’t need fins:-)

No fins on the LEM, Lunar Excursion Module.

But to answer your question the way it was asked, yes they would all “work” exactly the same and do absolutely nothing.

But “work” is a term in physics that first means doing something so it doesn’t really fit here.

Another reply would be, No. They are not doing any work at all, but they are doing no work in equal amounts.

See, once this stuff gets into your head and you start asking questions it gets very tricky and if the questions are not accurate then the answers are not accurate. So we first need to take our time to figure out if we are asking questions that will give us functional answers.

For example say you are a fin designer giving fins to a pro and asking them how they worked.

You might get an answer all right, but it might be all over the place and totally worthless to you. Whereas perhaps a better question might be “Did they track?”. Simple to the point. Yes or no. No guess work and you don’t have to start asking an inane line of questions that confuse the pro or rattle his cage. This is something I am working on actually. So it’s a good qestion. Thanks, Mark

79
Quote:

displacement needs to be offset by pressure difference …

the fuller the foil , the lower presure surrounding the surface of the foil …

bernouli’s rule , as the speed increases the pressure decreases …

a full foil operates in a region of lower pressure thus reducing the overall drag

This is not what shows up in testing…

Thin fins develop low pressure more rapidly, at smaller AOAs.

Bernoulli effects account for only a very small fraction of the lift from a foil.

Quote:

, a thin fin operates in higher pressure coz the water doesnt get displaced as far ,so if both fins covered the same distance , the extra water displaced is offset by a region of lower pressure water around the thicker foil …

the biggest problem here is presumption … we presume a thick fin is slower therefore it must be and we look for rational ways of explaining it …

it would be so much easier for me to make thin fins , but i make thick fins because they put magic into my boards …

i did the trial and error first before i learnt why and how via the text books …

when your testing surfboards and fins everyday for a living and find that everytime you put thicker fins on your board it goes faster , when you give boxes of different fins to teamriders and they come back and say "ok i still dont believe it but these fat ones go best "

Once you can define the relevant angles of attack, the problem becomes tractable.

As I’ve pointed out before, thin fins generate lift faster, at smaller angles of attack. Thicker fins need more angle to get the same lift. A reasonable attempt to optimize would be to make fins thinner and thinner until they are stalling prematurely, then thicker until they start to stall at the largest angles encountered. Then you get the most sensitive fins that will not stall.

Thicker fins absolutely reduce sensitivity to small AOA changes.

And, as I also pointed out numerous times now, my system is configured to NEVER stall. That being the case, thinner and thinner fins work better and better, I just find it too much trouble to make fins thinner by using epoxy and encasing in carbon fiber at the end. I’ll live with 6%.

I expect the optimal thickness will change with the application. In mine, thin was noticeably higher performance.

Another note on AOA. One of my early rotating boxes went 10 degrees. Sometimes, in finding the optimal rotating stiffness, it was loose, sometimes WAY too loose. Now, 10 degrees is far too much toe-in, and it was pretty easy to project that angles more than 15 degrees, averaged across the fin surface (for a single fin on the centerline), are never achieved (angles are higher at the base and lower at the tip). I was almost spinning out trying to get the fin to the end of rotation at 10 degrees!

There’s quite a bit of talk about AOAs, but this experiment made it a variable - the only control element in the hull couldn’t be engaged until you reached an AOA of 10 degrees. It’s funny because 7 degrees was pretty nice…10 was almost unrideable (with loose rotation).

80

If you add terms that control for speed you get a different set of answers.

Thin fins generate lift at faster speeds.

Thick fins generate lift at slower speeds.

Conversely:

Thin fins do not generate lift at slower speeds.

Thick fins do not generate lift at faster speeds.