Thanks for all the information you’ve shared. You’ve given us a great gift. Have a happy holidays, and take care!
Your famous (in my mind) airial was definately on a keel fin fish, and I am remembering dark green. It was on a right going towards the needles eye, on the inside section. I may have even been on a boogie board… lol. I don’t think I was older than 12. I remember you being pissed, since I was in your way, but I didn’t care (never have and never will… lol), I just thought it was AWESOME!
A thousand thanks Mr. Gall !
Some of the best advice this old grey beard has ever had layed on him.
You bet I wrote all that good stuff down.
Aloha Matty
impressively articulated engineering/field testing approach to nextgen board design and construction,
as it is, the surfboard industry is in for a major sea change once advanced 3D printing becomes ubiquitous
a time when forward thinking shapers with established technical chops are going to really hit the gas pedal
George, predict many speeding tickets in your future…lol
Hi Bob,
Yes, Gus is quite prolific, AND creative! I locate fin dots based upon several other factors in addition to the length. I look at width, bottom contour, rocker and in the case of Paipo and other prone craft, I like to see what config has met a lot of success. Lastly, I’d need to know the intent of the rider (down-the-line racing like Laniakea, or turns like Makaha,) oh and also the shape of the fins used!
Hi Harry! Thanks for the props, and you’re very welcome, it’s the least I could do, that’s what it’s for! And best wishes to you and the family! Happy Holidays!
OH MAN that is hilarious-!!! I can’t even picture you as a kid, ha ha!!! but seriously, that is dangerous to do to little kids, I don’t recommend or even condone it (unless either money or good waves are at stake…) I don’t remember that fish, most were dark, either black or very dark blue/purple they go faster.
Hi Matty! Very cool, if you get a chance PLEASE follow up with any developments. That is one thing that lacks on this site sometimes, those requested changes and the ACTUAL outcomes are GOLD to somebody out there… …don’t know who yet, but they’re out there!
@Icc-
You know what? It’s funny, I just realized that shaping has ALWAYS been a “subtractive” process. With the 3D Printer, “shaping” (or projecting ones’ will to a goal of a shape,) is an “additive” process. Very cool. It’s already happening, fins, hardware, and board/rail sections, so we wait…
“George, predict many speeding tickets in your future…lol”
Oh and fast fun ride it will be…
Best regards,
George
As posted earlier in the thread by George/PlusOneShaper:
"Don’t mean to bust your chops, but because you’re an Engineer I have to say something about nomenclature. (I realize you’re area is Hydrauics/Fluids/Civil so maybe you can school me on this. “Cavitation” is boiling and subsequent collapse of a fluid…
…I think the term “Separation” is what we are talking about (true surfboard fins produce LOW pressure but nowhere near the magnitude of a viscous coupling,) in which flow becomes so low on one side of the fin, that the laminar flow actually “detaches” from the fin and turbulent, not lift-producing flow, results. Once this smooth flowing water gets ripped away from the fin, it is very hard to re-attach, unless some sort of “influencer” is used."
Hooraaaaaaaay!!!
'Taught myself some high-speed hydrodynamics a fair while ago now and it’s always bugged me whenever I walk into a surf-shop and ask the sales assistant to tell me about the new fins the shop’s just got in, and they start banging on about how the fins will “cavitate” and release/slide out just when you want them to.
I’ve tried explaining to them that while a tow-in or big-wave surfer might get up to cavitation speeds (~50knots/93km per hour/57mph), the average surfer gets nowhere near that fast on a wave**, and if there was honest-to-god cavitation going on, you’d know about it because the imploding bubbles of steam would be eating the fins alive. The cavitation pitting would be plain for all to see.
I’ve largely given up on that though as you can see their eyes start to glaze over and the info going straight over their heads, so now I just grit my teeth and put up with their talk about “cavitation”. Most of the time they’re kids who’ve at best never experienced anything more advanced than high-school physics, so they can be forgiven for that.
But fair go, this is Swaylocks - a place for the propagation of the truth about surfboard theory (or at least I believe it’s supposed to be) and a source of education for those who wish to learn it, so it’s important that the concepts talked about here are correct.
I’m not trying to have a go at GregTate here, it’s just that I’ve seen quite a few users in the past posting on Swaylocks about “cavitation” when in fact they mean “separation”. 'Time that was put right, so points to George for striking a blow against this “cavitation” at sub-cavitational speeds misunderstanding. Spread the word folks.
And GregTate, please, if you catch me goofing up on a concept in the future, let me know about it and set me straight; I’ll meekly accept as I’d much rather know the truth… (I wonder how long I’ve got before that happens; probably not too long because as is usually the case, the more I learn, the more I realise I’ve yet to learn :) ).
**I do vaguely recollect it is actually possible to deliberately induce cavitation at lower speeds (around as low as 36 knots if memory serves), but standard off-the-shelf fins don’t have those features.
Cheers all.
George,
Lots to ponder over - thanks again.
Bob
LIT. No offense taken. You and George are correct. My last hydraulics course work was in 1972. I just lumped it all into cavitation as short-hand for the mild to severe disruption of laminar flow. But you are correct that that is technically very incorrect.
I just didn’t want to miss an opportunity for George to talk about how fins disrupt laminar flow and how fin placement can help
And another thing. It happens in 3D not just in a plane like the text books show. Lots to explore here
@L.I.T.-
Yes, I posted that only because I am too comfortable with Mr. Tate, he is a sharp engineer and one heck of an athlete swimmer/surfer who has a good habit of making things happen. I too tend to “tune people out” as they invoke “the cavitation thing” in surfboard design, I just wanted to be sure Greg wasn’t “one of those guys…” (I was helping, Greg!)
Greg knows more about flow and surfaces than anybody on here, he is being too humble,
some examples of Cavitation:
Okay guys, kind of a quiet evening. I want to throw this out there. One morning about 30 years ago, I was sitting through an Aerodynamics class (we had to take cross-curriculum, so if you studied Electrical Engineering, you’d take some Civil Engineering, Mechanical Engineering and Aerospace Engineering to round out your experience. There were only 4 disciplines of Engineering back then, instead of the 12 plus now.) The professor spent a good 20 minutes going over the concept of lift, like you see in those social studies movies way back then, how low pressure forms over the top surface of the wing because air must travel further than the bottom surface to get to the rear edge of the wing at the same time. He had 2 chalkboards full of bitchin’ drawings and stuff, turned to us and asked, " Are there any questions?" My hand went up quickly…
Prof: “Mr. Gall?”
Me: “So, how can a plane fly upside down?”
His nice ‘good morning’ smile inverted, and he turned red. I could feel the vibe in the class, “ohh shit, George again…” and I admit, I was a dick back then, way worse than now.
Most planes can fly upside down. Most can do this for long periods if pressed. It may not be efficient but the plane flies…
So,
“How does a fin REALLY work on a surfboard?”
(who wants to be in the Hot Seat now?)
Could you please post up a few pics of your work, with a little description of the boards?
Hi George, I’ve really enjoyed the technical aspects of this discussion and maybe I can add something on the cavitation part.
The definition of cavitation is confusing, even in engineering circles, since it is often modelled in many different ways. I’ve done a lot of study using cavitation as a cutting force for micro-surgical tools. This was generally a 3mm piston moving at 40 kHz at .0005 inch stroke in water. Cavitation was a result of the water collapsing in the void left when the piston retracted. This looks like bubbles under magnification hence the term “cavitation bubbles” . What really happens is that extremely high temperature spikes are created during the collapse of the void (since it’s essentially a vacuum) which will vaporize anything in that was in there (3K + degrees). I found that the lower the frequency of stroke, the more intense the temperatures were as the void collapsed more slowly. The higher the frequency, the forward stroke of the piston would interfere with the collapse and the temps were lower. Cavitation on spinning objects is harder to understand due to centripedal motion and such and I hope the linear example helps those interested in this subject.
I feel that in surfing we plane on the inside surface of the fin , the outside foil adds to that .
Template shape is very important in creating and controlling this lift along with its placement .
Hows that sound ?
Gregory of the interweb ;-)
"Most planes can fly upside down. Most can do this for long periods if pressed. It may not be efficient but the plane flies…
So,
“How does a fin REALLY work on a surfboard?”
Most pilots are still taught this concept and don’t truly understand the implications. It’s all about the Angle of Attack. Aerobatic planes which are designed to fly upside down have symmetrical airfoils, so that in inverted flight the Angle of Attack determines the lift vector, not the airfoil. Like you said, it’s much more ineffecient with assymetrical airfoils, but they can do it, although there is a ton of drag involved.
An intersting concept in aviation is using an Angle of Attack indicator instead of the airspeed indicator (which can vary with altitude and temperature) and purely using the AoA Indicator to determine best flight paths for takeoff and landing - http://www.navyair.com/Angle%20of%20Attack%20Indicator.htm
In surfboard verbage we refere to Angle of Attack as Toe-in on multi-finned boards. On singles you change the AoA by turning the board.
There is such a complex interaction between the board bottom, fins and rails that it’s evolved mostly by empirical trial and error.
That’s my .02. Obviously, so many different things “work” and surfing is SO subjective it’s really hard to say what works “best”. It’s more what works “best” for the feeling your after. Some guys like to fly stunt planes, some guys like to fly gliders. They both work, but in very different ways with very different techniques.
Question: what is the general width for tail block on a traditional mini simmons? I thought I heard 14-16"?
And what is your take of a dead flat traditional mini vs rockered one? I dunno, but something tells me to go orig.
George,
You mentioned earlier that carbon cloth has greater compressive strength than FG.
If you only had enough carbon cloth to do one side, which side would you laminate with it. Top or Bottom? Why?
Thanks for all of the informative responses in this thread.
Bill
Ding Ding Ding!!! Winner!!! (and there’s more too)
The majority of “lift” from our surfboard fins come from the “other” side of the fin. Before I explain, this has been verified by two other shaper/board builders, and now there are two theoreticians who are concluding the same. Warning: Fin Foil (as mentioned,) does help, a little…
…the fin acts as a “fence” (yes that’s a technical term for it,) to the lateral flow. A fin, (or Vane) can be placed in that slipping flow to “grab” or divert flow momentarily. I am thinking about the outer (side) fins on a cluster of fins, but this is true with singles, on up.
And let me qualify this further, this is just for the “hold” aspect of the fin, NOT streamlining it.
The concept is called “Dynamic Lift” which can be exemplified by sticking your hand out the car window whilst traveling at speed. The AoA (Angle of Attack,) is the thing to consider. With your palm down, going 60mph (95kph,) you will find a “neutral spot” where your hand neither dips down or folds back. If you bring your fingers up (increase the AoA,) your palm gets hit by the rushing air and makes your arm flop back. This is Dynamic Lift.
We tested a set of fins with NO foil, picture the fins cut out to a shape but square edge all the way around. They worked, a little draggy but surprsing that they held so well. We then round the edges off, since we suspected flow separation at the sharp corners, and the fins felt just about like “regular” fins. I “think” the fins may be a little draggy compared to regular, but the trade off was they had great release on off the lips.
This exercise led to the understanding that fin foil was only a small contributor to performance, as Greg pointed out. On multi-fin boards the “cluster” of fins/fences act to contain pressure under the board, and the bunched water acts as a hydraulic dynamic spring, that a surfer can push off of, or leap from into another move. So, in designing a board, have in mind that you are “fencing in” fast water flow, with the fins, then letting it go somewhat elastically. “Could this be why so many shapers have double concave running through the fin area?” Maybe. The way we do boards is, we look at what’s going on, build one, then try it. The ones that feel best, survive and propagate. Then something else is tried. Feels right. Continues. NO theories, just trying stuff. If the rider/shaper/designer is honest enough in their assessments, the designs will develop. This is where we are now.
It is only in the last 3-4 years that I’ve designed boards more around this concept and have met noticibly good results. YET, I STILL USE regular fins… …ARRRGGHH. Hypocrite! I can’t sell boards that look like that, I can explain as much as I want: no sale. And I have to sell boards, because that is my livelyhood: pressure.
Lastly, I wanted to mention that the regular thruster fin set up you see, is NOT “camber matched.” That means the center fin should be TWICE as thick as the flat sided front fins. That bugged me for a long time, so I tried it, with only marginal results. But then after I realized that Dynamic Lift is the main player, it all made sense.
The squared edges of this Dynamic Lift fin should probably be built with the leading edge shockwave in mind, AND with maintaining “flow attachment” at high AoA’s. So sharp is not a good idear. If you are into trying this, try 1/8" Radius all the way around the outline of a fin that’s 1/4" thick. Both sides? You tell me, you want symmetric or asymmetric attachment properties?
Furthermore, most all surfboard fin templates are not optimum, but that’s a whole other “exercise in futility” that I won’t go into right now. ha
[edit]
Oh, an afterthought, I meant to follow up on this.
“There is such a complex interaction between the board bottom, fins and rails that it’s evolved mostly by empirical trial and error.”
Yes! On point. There is an augmenting effect with this “bunching up” of energized water. The effect seems to be caused by the base of the fin interacting with the board. This is truly counter intuitive to everything I was taught, like “baseless” fins and “elliptical football” outlines. The augmenting effect feels like massive amounts of drive as you pump or rollercoaster a board for speed. The longer the base, the more this effect, which is probably why I’ve gravitated toward the fish keel fin to promote this one aspect. This drive effect is countered by less freedom in yaw however. I just wanted to mention this when considering “fins as flow fences.” My fish fins have 8" plus long bases, up to 9". This is sorta why channels/gutters work, but they don’t work as well given the wasted area presented.
I have a lot of pics on my and my company’s Facebook pages. I kinda don’t want to put too much on here, as it can be seen as me “selling my wares,” which I am not into in General Discussions.
Hi Pete,
That reminds me I’ll be in contact with you for some more of your custom valves, thank you so much for providing this product! Oh, and I have a planer that was in a fire, which I have questions about… …anyways,
“I’ve done a lot of study using cavitation as a cutting force for micro-surgical tools. This was generally a 3mm piston moving at 40 kHz at .0005 inch stroke in water. Cavitation was a result of the water collapsing in the void left when the piston retracted.”
Oh man, that is such cool stuff! And yes that tracks well with classic Cavitation scenario. And a great use as an industrial tool, amazing!
I always refer to “two ways to boil a fluid” one is to heat it, the other to lower the surrounding pressure. I tell guys, you can boil water at ROOM TEMP, just lower the room pressure. Same with the human body, or any fluid. With pistons I totally see how low pressure or vacuum can be created. It is a little harder to see with racing boat propellers for example, but it has to do with Dynamic Lift (as mentioned,) but focus on the “other side” of the prop blade, that has just dug out a groove in the water. One side of the Prop Blade grabs water and provides thousands of pounds of thrust to push the boat (drag boat,) and once that void is “dug out” of the water, the back side of the Prop Blade is in an incredible VACUUM, and the water (say 60 degrees F,) flashes to an instant boil. The bubbles are microscopic, and as quickly as they form, they collapse. The bubbles collapse “asymmetrically,” directing the collapsing energy toward the surface of the prop. The little “pinging” collapsing energy tears molecules of metal off the Prop Blade. The metal doesn’t go peacefully so some heat is given off (kinetic energy transfer.)
I love your description of how to “throttle” a cavitation for milling purposes, WOW. Thanks!
@shapaholic201-
14 to 16" tail blocks sound about right, but I’m sure there is no “rule” to it. I had Joe Bauguess shaping out of my shop for two seasons, he shaped the first modern Mini Simmons, and he had set templates. He said he basically used what Bob Simmons did and sectioned the board shorter. That might be a good reference, either looking at Joe’s templates or at Simmon’s boards. Good luck with it, and realize Joe has the rights to the name “Mini Simmons” if you plan to make any money off the use of the name
Hmmm, I said that carbon graphite is an Engineer’s favorite, but as a surfboard builder, I don’t like complete encasement of a board in graphite, WAY TOO RIGID. That said, to answer your question, I’d go against what I’m seeing coming out of China and Thailand and use carbon on the deck. Assuming you surf without bindings, you can only apply weight to the deck, causing the board to deflect downward. The fibers in the bottom of the board would pull tight (tension,) and the fibers in the deck would cram together (compression.) Carbon graphite would counter this compressive load. Again, it might not be so desireable. Plus there are other load scenarios whic might take precedence like the board snapping in a gnarly wave.
With racing SUPs and some sailboards and kiteboards I would use graphite encasement.
Hope this helps.
Best regards,
George
So for this scenario, what takes precedence? Carbon on top?
i played a pretty good prank on one of my buddies during a surf trip by switching his side fins (so the flat side faced the rail)
he is a really good surfer and was still ripping - i was bummed that my prank did not work. but then he mentioned that he was having a hard time that session then he saw the fins were backwards and thought that they had been backwards for the past few days and thought he had stumbled onto something great since he was loving his board for the majority of the trip (except for the last session which he blamed on the waves). Turned out to be a good prank - the whole crew had a good laugh at that one!