SHAPER's HOT SEAT: George Gall

127 posts |
Last post
stoneburner's picture
Joined: 12/30/2007

George,

We were robbed of 2 days interactive dialogue with you when the forum went down...

Can you explain what hydrodynamic benefit toe-in gives fins on quads and thrusters?  How?

Thanks,

Bill

like
1

Swaylocks Surfboard Design Forum: thoughts & theories ... practical & theoretical

RAIL PROFILE http://bgboard.blogspot.com/2014/03/march-82014-afterr-seeing-recent.html

peterg1's picture
Joined: 07/17/2006

I can see the major side panel Invee, and maybe  faintly some micros in the tail and I guees theres another forward broader more shallow one?,  all running parallel to the stringer.

We've all seen the photos of  a board in a hard bottom turn, hard on rail and the water traversing across the bottom at maybe a 25 to 35 degree angle or so. Does InVee confuse/ aerate this water flow or attempt to straight channel control  it? Is there control in this "lively" feel?  Is it looseness and the ability to change and quickly reconnect drive and stability?

Your rail  cross section shows a domed deck into a very radial  airplane wing foiled rail...how blady and tappered  does this get toward the tail?

Alot of the traditionalist say keep these guns flat to panel V front (for chop and out the tail (for Control). I know the control of radial convcaves ability allow rail to hook, hold and drive when on edge... water follows the funnel, where as a panel vee would tend to cork and slideout except for reliance on fins hanging in 2 feet back,.... especially in cross chop.

With Invee you are doing both the opposite and the same thing as tradionalist since two invees side by side give a center Vee..AND the rail has its own Half Vee which is like a water hook on the railine.

Things get a lilttle confusing when theres still  another set of invees in the tail becoming almost like a "multi channel" bottom one would not typically associate with a big wave gun.

When I think of dramatic Vee and Invee... the older 13' Boston Whaler hull comes too mind and one can turn those at high speed on the gunwall.

like
0
oneula's picture
Joined: 06/10/2004

here's the board that gave the inspiration for his invee

i've been riding one since the early 2000's after having detailed discussions with Rand Hogan

looks like a quad surfs like a thruster

http://mkdesignmarketing.com/gemini/

http://www.theinertia.com/surf/riding-the-gemini/

http://www.surfermag.com/features/gemini/

http://www.lalasurfboards.com/gemini.html

like
0

"ain't no big ting brudda"

greggriffin's picture
Joined: 05/09/2005

First time I heard the words " Inverted Vee " was at T&C around 1986 

When our boards are working their best the front 1/2 to 2/3 are not touching the water .

Maximize the efficency of each part of your total design , board and the fins designed as part of that design .

like
0
Huck's picture
Joined: 12/07/2009

greggriffin wrote:

First time I heard the words " Inverted Vee " was at T&C around 1986 

When our boards are working their best the front 1/2 to 2/3 are not touching the water .

Maximize the efficency of each part of your total design , board and the fins designed as part of that design .

Was there a question in there for George?

Cuz otherwise best save it for your own week in the hot seat  :-)

-------

a pic like this is worth a thousand words!

like
0
greggriffin's picture
Joined: 05/09/2005

Huck

that was my response to bernie's post above .

This posted rail shape makes me happy  :-)

like
0
peterg1's picture
Joined: 07/17/2006

I dont know it ...know of it.... not many crossections available...... this looks like a single InVee (Tunnel) inside broader InVee across rail to rail  and looks to blend almost radial concave out the tail..hard to tell without a straight edge

like
0
PlusOneShaper's picture
Joined: 03/19/2004

@greggriffin-

Hi Greg, "T-Boy" is Tom Gaglia, originally from Newport, moved to Maui and during that creative period, shaped a board called "The Rubber Band" for his friend Garth Murphy, (the board that Mike Hynson saw when he went over visit the group during the 60's.)   Shoots! I missed the 60's, (first rode a wave in 1969,) but those Masters have since shared their stories (and design developments during those times) they are an incredible bunch of surfer/shapers.  Tom is a very good friend of mine who comes up to shape at my place several times a year and he still rides a shortboard (Garth too, somtimes...ha, just turned 70.)

@bgreen-

Hi Bob, I just saw the Acosta Paipo photos.  Let me say that guy is NOT afraid to try stuff, AWESOME!!!  The "Dragger" I had in mind is similar, but sould not have any foam on it, or any thick structure at all (this is why I said it would be dangerous to try.)   I envisioned a few layers of glass, or maybe stiff silicone rubber or urethane.  The dragger would bend VERY easily, BUT NOT flutter, that would be bad.  Heck, you could even tie a rag on the corner of the board to get some benefit!  BTW, check out some of Acosta's bottom contours-!!!  Being that low to the surface of the water at speed, just AUGMENTS the effect, I wished he would post on here...  

...Who is next in the Hot Seat?!??

@stoneburner-

Hi Bill,

"Can you explain what hydrodynamic benefit toe-in gives fins on quads and thrusters?  How?"  

Oh man, I'll try to be brief, I've thought about this a LOT over the years and I think I'm starting to wrap my head around it.  Obviously someone a way long time ago figured it out, probably started soon after more than one fin was put on a board. The earliest instance I've seen personally was a Bob Simmons two finned board, that to this day has a feeling of being from the future/alien abduction kind of thing, creepy, the board is late 1940's-early 1950's yet has features we use now.  

Multi-finned arrangments tend to be compromises, that is, at any given instant, one fin is doing more work than others and the other fins are momentarily "just along for the ride." A good example of this is when doing a hard bottom turn, have a look at a photo and you will see the shoreward fin will be completely OUT of the water, leaving the share of the load on the remaining fins (in the case of a thruster, the remaining two fins.)  Of the two remaining fins one is doing more work than the other.  Again, in the case of the hard bottom turn, the fin furthest from shore is doing the most work, with the center fin adding a portion of the help.  

"So WHY are they angled all differently?" As the focus of turning effort is put upon one fin, the slight angle (or "toe-in",) acts as a TURNING rudder, kicking the tail over to set up trajectory of the rest of the turn.  Years ago we validated this using the South African designed "4 Way Fin System" which let us change the Toe-in angle.  We even tested "Toe-OUT" in the set up, surprsingly it worked well for generating down-the-line speed.  As predicted the "looseness" was horrible.  With the 3 fins all pointed straight ahead the board was likewise too stiff.  We even tested extreme Toe-in and it was very loose but also the inherent drag was too high (picture the "Snow Plow" move that skiers use to slow down.)

All this said, I am guessing there is a second thing going on.  I think the flow off the tail is NOT all straight, but flares out kind of in the radiating pattern like the fins.  As the surfboard skims atop the water, the "supporting" water seeks the low pressure, which is to escape to the nearest edge of the board.  As the supporting flow travels tailward, the water that "escaped" out the sides (seen as rail spray, even in straight trim, not just turning,) must be replaced by water coming into that zone, thus the radiating pattern.  Of course this is just a snapshot in time, because as the board turns, the flow does NOT run parallel with the stringer but diagonal (supported by numerous pics and video of underwater surfboard shots.)  This diagonal flow is called the "spray route" and it changes continuously as the board is turning and re-adjusting to the moving wave.

Articulating fins are a good concept to address the variable flow patterns.  I recall a member here "Blakstah" had a system which did this but I never had the opportunity to try it.  I use "rake" in a fin to allow for variable geometry.  The Wright Flyer was an aircraft which used twisting wings to control its' flight.  The main function of rake is to induce bend beyond what is normally there into the fin.  Any bend of course will create drag (picture the Wright Flyer bending a wing to turn,) so it is a safe bet to say "if your fins have rake, they will drag more than running flat at some point."  I should say that drag is a very necessary component to having a fin.  If the fin generates lift, it will do so at the cost of drag, hence the "lift to drag ratio" of all foils.

So one last part to the puzzle.  Back to that bottom turn, the shore side fin is out of the water and the fin furthest from the shore is doing the "lion's share"of the work.  Well, that working fin is ALSO BENDING, so it is dragging, MORE than running straight, and MUCH MORE than the fin that popped out of the water (water being 400 times more dense than air...ha)   Picture a rider on a Head First Luge sled, dragging their foot to change direction, that is ALSO happening with our fins.  Skiers do this with ski poles as well, heck WE do this too!  We will drag a hand to turn, and our surfing forefathers dragged a foot to turn!  This is normal.

@peterg1

You are right on track (no pun!)  The inverted vee is lively and under control, almost like it's riding on a soft flexy rail, I found that directionality is there, so I can run SMALLER fins, thus have less drag, thus MORE SPEED! yay.  

"We've all seen the photos of a board in a hard bottom turn, hard on rail and the water traversing across the bottom at maybe a 25 to 35 degree angle or so. Does InVee confuse/ aerate this water flow or attempt to straight channel control  it?"  

That traversing water flow is called "Spray Root," I learned that in discussions with a great board builder, Doug Vickery, and later I turned Maurice Cole onto the concept when he shaped at my place. Maurice and I had many a discussion about the concave (he, is "Mr. Concave" ha ha,) and the "lift" many think the concave produces.  Well, really, it doesn't.  In fact we found that bottom contours forced the rails to ride deeper in the water.  MC was far ahead, he even sharpened the rail's tucked edge from NOSE to TAIL.  This allowed the deep penetrating rails to "cut" through the water and stay deep.  Basically the net waterline of the concaved bottom is DEEPER than a flat bottomed board*, HOWEVER as speeds increase the concave DOES lift a bit due to flow containment.  Enter the InVee.  As speed increases, that lift vector is not as exponentially high as we go faster.  I do not yet know fully how it works to get the "feel" that we are feeling, but so far the indications are positive regarding surf-ability.  One thing the deep concave boards do not do well is airs.  I am thinking a deep InVee will not provide a good platform to leave the water either, so use it in moderation.  

Now. The LATERAL component of the Spray Root.  In a concaved bottom, the water particles moving laterally change direction continuously on their translation to the rail, because they are travelling along a curved surface. Rusty said it best, "Think about every shaping feature you put in a board, because it costs to move water."  This is so very true.  With the inverted vee, the direction change (obviously,) is once, IF that, which is the part I am not sure on.  My question to myself has been, "Does the lateral component of the water hit the inverted vee and get disturbed, or does it become more laminar?"  Now I am suspecting the latter.  Which is why I put (as you've graphically pointed out,) multiple inverted vees into the bottom.  First, to progressively keep the waterline down in that part of the board (for holding power) and second to slightly redirect spanwise flow for a little bit less drag.  The contours act to "comb" the flow.  The feedback has been good paddling (low speed dynamic) and great speed (hsd.)  The board also rolls over on rail well, which was the major concern some true expert big wave riders had (and probably the reason many shapers stick to regular belly/vee configs on their guns.  (Note: We are seeing more concaves in big wave boards due to their success being used in the Tow Boards, mostly single cons with double concave combos of some sort.)

"Your rail cross section shows a domed deck into a very radial airplane wing foiled rail...how bladey and tapered does this get toward the tail?"  

That was the challenge of that board- it took me a year to design and I wasted another 10'8"BG in the process (long story,) but I managed to get the 10'6" x 22-1/8" x 4" package  to have a decent rail volume for given width.  The tail-rail is not that bladey, but I should note there is NO vertical sidewall in the rail.  I spent a lot of time scrubbing the correct rail shape into the pre-cut, and I also glassed it myself on the re-glass (board was glassed twice (for strength and increasing the weight,) in order to get the shape of the rail right after all those glassing laps killed it.  The surfer is 145-150 lbs w/o suit, so imagine trying to keep a 10'6" x 22+ from flapping once up to speed.  If I bladed the rails too much I would risk a bad oscillation mode, which I learned from making speed sailboards, where too much water will momentarily "grab" the rail/deck, causing the rider to check himself, which then changes the trim, causing another "grab" etc.  This is pretty subtle stuff, but VERY distracting to a surfer in 30+ who is focusing on just trying to make the shoulder via a single good turn.

Agreed, the vee bottomed boards put a lot of unnecessary load on the fins (so the designer puts bigger fins on the board = more drag.)  Minimize the fin and the board will go faster in high energy situations.  (Almost the opposite is true in the converse.)  

"Things get a lilttle confusing when theres still another set of invees in the tail becoming almost like a "multi channel" bottom one would not typically associate with a big wave gun."  

Yes, the attempt is to have the contours "trip" the flow to keep it attached and smooth for the rider's sake.  I can't stand "flappy guns" (pitch oscillation.)  And yes, this is my attempt at trying something that's never been done in giant waves.  I feel very fortunate to be working with guys crazy enough to give it a go.  So far it trialed well, even with off-the-shelf fins, which is an accomplishment already.  Stoked.

re. Boston Whaler.  LOTS of those growing up here!  You could turn those so hard that you could hurt yourself, ha!  Smooth runners too. Didn't make that association, but it is a good one, marine architects have been through a lot of designs, like Jeff Alexander following the Unlimited Hydros... ...there's money at stake!

Anyways, keep the rail set, and remember that concave AND invee both have MORE ROCKER at the rail than down the stringer- another plus!

Hope this helps.

Best regards,

George

*conversely a vee bottomed board has a net waterline deeper than a flat bottomed board, but it is not deepest at the rail, so SET YOUR RAIL before going into a turn!

like
1
bgreen's picture
Joined: 10/21/2007

Hello George,

Lots of Gus' designs here - http://mypaipoboards.org/interviews/GusAcosta/GusAcosta_2012-07-21.shtml

I'm not sure he's a forum sort of guy, but happy to communicate.

My last question -  where would your fin dot concept place twin fins on a 53" board?

Bob

like
0
sharkcountry's picture
Joined: 03/25/2006

Thanks for all the information you've shared. You've given us a great gift. Have a happy holidays, and take care!

like
0
obproud's picture
Joined: 05/10/2007

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! 

like
0
mattwho's picture
Joined: 05/12/2014

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

like
0

I would rather be someone's shot of whiskey, than everyone's cup of tea.

www.mattysurfboards.com

lcc's picture
lcc
Joined: 04/24/2008

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

like
0
PlusOneShaper's picture
Joined: 03/19/2004

@bgreen-

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!

@sharkcountry-

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!

@obproud-

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.

@mattwho-

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

like
0
L.I.T.'s picture
Joined: 10/08/2014

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.

like
0
bgreen's picture
Joined: 10/21/2007

George,

Lots to ponder over - thanks again.

Bob

like
0
GregTate's picture
Joined: 03/18/2004

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

like
0

Personally I'm always ready to learn, although I do not always like being taught. - Winston Churchill

GregTate's picture
Joined: 03/18/2004

And another thing. It happens in 3D not just in a plane like the text books show. Lots to explore here 

like
0

Personally I'm always ready to learn, although I do not always like being taught. - Winston Churchill

PlusOneShaper's picture
Joined: 03/19/2004

@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:

like
0
PlusOneShaper's picture
Joined: 03/19/2004

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?)

like
3
greggriffin's picture
Joined: 05/09/2005

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  ;-)

like
0
Huck's picture
Joined: 12/07/2009

Could you please post up a few pics of your work, with a little description of the boards?

like
0
petec's picture
Joined: 03/18/2004

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. 

like
0
lawless's picture
Joined: 05/21/2004

"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.

like
0
Clamsmasher's picture
Joined: 02/06/2013

HI Lawless,

Actually toe in on a board should be referred to as "angle of incidence". The angle is fixed at manufacture on aircraft as it is on a surfboard. A few aircraft have been made with variable incidence wings, used to control body angle vs AoA at very low airspeeds.

AoA is a variable determined by the angle of the foil relative to the air or water flow.

like
0
shapaholic2011's picture
Joined: 01/04/2011
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.
like
0

"Freestyle."

stoneburner's picture
Joined: 12/30/2007

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

like
0

Swaylocks Surfboard Design Forum: thoughts & theories ... practical & theoretical

RAIL PROFILE http://bgboard.blogspot.com/2014/03/march-82014-afterr-seeing-recent.html

PlusOneShaper's picture
Joined: 03/19/2004

@greggriffin & @lawless-

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.

@Huck-

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.

@petec-

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

@stoneburner-

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

like
0
stoneburner's picture
Joined: 12/30/2007

PlusOneShaper wrote:

precedence like the board snapping in a gnarly wave.  

George

So for this scenario, what takes precedence?  Carbon on top?

_____

like
0

Swaylocks Surfboard Design Forum: thoughts & theories ... practical & theoretical

RAIL PROFILE http://bgboard.blogspot.com/2014/03/march-82014-afterr-seeing-recent.html

grasshopper's picture
Joined: 03/18/2004

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!

like
0

https://instagram.com/grasshoppersurfboards/ 

oneula's picture
Joined: 06/10/2004

grasshopper wrote:

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!

too funny

years ago when they first came out, I committed the ultimate sin and put a 4 1/2" thruster set of Donald Takayama's Halo fins on my custom 5 fin fish Greg Griffin made me.

As I rode it I kept thinking "wow, these fins ride pretty well pretty loose"

It wasn't until I came out of the water and walking op the beaaxh to the shower that one of my "friends" called out from the peanut gallery, "Eh brah, what you doing?,  you got the back fin on backwards brah!"

I brushed it off with a smile and acted like I did it on purpose (being the mad surf scientist and all) but I felt like an idiot. 

It did teach me that being open minded means anything is possible.

 

like
0

"ain't no big ting brudda"

PlusOneShaper's picture
Joined: 03/19/2004

@stoneburner-

Sorry Bill, yes, the deck, but again, it is quite stiff...

@grasshopper-

I think they call that a "single blind test" ha ha.  Great example- I'd figure his whole world woulda come unglued, but now it makes sense he kept surfing, ha

Best regards,

George

like
0
lcc's picture
lcc
Joined: 04/24/2008

"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"

best explanation yet for the force mechanism of multi-fin boards. 

"that a surfer can push off of" - and there's the rub.  Height/weight/foot size differences = major force differentials.  Front footed, back footed apply it differently as well.  Why a magic board for me can be a dog for you.  And usually it starts with the rocker and fin(s) placement.

so, George, if you don't mind sharing what well may be trade secrets, what's your rocker differentials on a fairly conventional 6'4 thruster for a front footed surfer vs. a back footed surfer, where would you land the respective fin clusters, and what else would you change in the shape?

like
0
PlusOneShaper's picture
Joined: 03/19/2004

@Icc-

There's several things happening in this design push.  The "front footed" surfers tend to surf "horizontal" and the "back footed" go "vertical" more.  Both types also cross over a bit.  Dedicated front footers will get a dropped tail rocker from me, but standard fin positions.   Sometimes I will not drop the tail rocker but I will let the rocker run low aft of center then accelerate it up just at the fronts of the front fins.  I will not drop the water entry however to keep the board free in yaw, but I might drop the nose rocker a bit, mostly for looks.   Relavent numbers might be 5-1/4" nose and 1-7/8" tail.  I will also move the widepoint slightly forward maybe 2" aft of center but as much as even with center.  The bottom contours may initiate further forward, like the "doubles through the fins" might start several inches further forward.  I would also not make the doubles flare out as much, kind of "matching" the chosen rocker.

With backfooted surfing, I may keep the rocker in the tail low, say 2" but usually will flip it, aft of the rear edges of the front fins, and continue the acceleration of the rail rocker, perhaps resulting in what looks like "vee" in the tail.  One thing is I would shift the front fins back about 1/4" (this forces the rider's "neutral stance' to move back an inch or two,) and also bring the wide point aft, like 3 to 4+ inches aft of center.  I might leave the center fin as is, for more yaw, but depends upon the surfer, if they throw their board around like that or not.  The bottom contours might shift aft a bit, with focus on doubles (for example,) having a more exaggerated "max depth" about mid-fin with the front fins. I like to flare these contours out behind the front fins as quickly, yet smoothly as possible and the template/foil/rocker will allow.  A lot of times I will soften the forward rails a bit, making the tucked edge go away a bit in the last 18-20 inches of the nose.

This is NOT the "be all, end all" as I have various models of boards that cross over and allow for both modes of surfing, as many shapers do.

Hope this helps.

Best regards,

George

like
0
mattwho's picture
Joined: 05/12/2014

Mr. Gall,

1st Thank you for the meat (valued information)

And it would appear you have set the record for time spent in "the hot seat".

My burning question would have to be the single concave.

The Maurice Cole tow in board haul's ass and was hard to ignore.

Been working on low energy single concaves for about 3 years now, using a number of different entry and rocker ideas.

We touched on “nose rocker” and I’ve got some new stuff in the works.

Very aware of entry rocker and flow thru both double and singles.

If I may can you give us you astute opinion?

Mahalo Matty

like
0

I would rather be someone's shot of whiskey, than everyone's cup of tea.

www.mattysurfboards.com

offshore's picture
Joined: 04/20/2008

George,

Thanks for all the amazing information. Still soaking it all in. 

If you are still in the hot seat I was wondering if you have experimented altering fin cant and its effects on performance, particually with regard to quad setups.

cheers

like
0
artz's picture
Joined: 02/01/2007

  This might be worthy of its own discussion a question for all our engineering types out there.  We Have lots of talk about the design of boards and fins. Yet I feel that how and what we use to build boards might be the biggest change in surfing.  For the most part we have been building boards the same way since the 1950s. Epoxy isn't all that new. It's been made much better in the last 10 years However the basics are still the same fiberglass reenforced plastic shell over a foam core.  Aero space engineering has made some advancements with materials over the last 50 years or so. High Performance jets use a lot of different materials 

So Engineering geeks whats out there that just might make a better Board?
like
0

According to Mikki Dora Malibu went to the Dogs in 1964. The Chumash Indians will tell you it was 1664.

shapaholic2011's picture
Joined: 01/04/2011
Ty George! Not planning to use the name, but ty fti! I actually wasn't aware Joe designed the mini until last mos! :)
like
0

"Freestyle."

lawless's picture
Joined: 05/21/2004

Wow, thanks George for sharing so much knowledge. Always nice to hear insight from the guys who have really experimented and have a ton of experience.

Artz, to this comment - "Yet I feel that how and what we use to build boards might be the biggest change in surfing.", I went down a path a number of years ago to get a much more durable board and have settled for now on stringerless EPS, with a cork deck, all vacuum bagged. It's still old tech as far as other industries are concerned but it makes for a light, durable board. Honestly, stringerless EPS, bagged with 4/4/4 deck and 4/4 bottom is a pretty bombproof construction while still being super light and cheap. Using s-glass instead of e-glass makes a big difference. The problem I see with most of the "tech" builds is that it's done mainly for marketing and not actually because the materials are performing a specific task unique to their properties. I'm a big fan of KISS, over-engineering things can be as bad, if not worse than under-engineering them.

Another thougtht I had about our obsession with the nuances of boards after hearing George talk of testing un-foiled fins, was how much of an overall affect do our boards have on our surfing? I realize my style has some glaring flaws and yet I still pursue more refined boards without putting nearly as much effort into actually refining my own technique. It's a very humbling approach that I think most aren't willing to accept, to not point the blame so much at their equipment, but instead look at their surfing style first to make the biggest performance gains. Bit of a digression from the discussion, but notice in a lot of these design discussions the rider is not included as a component to be tweaked and optimized as a part of the system, when we likely play a much larger role in it than the boards we ride.

It's still fun to geek out and try and optmize and refine things though and get a better understanding of how they actually work. It helps a lot to have a clearer understanding of that complex interaction that goes on beneath our feet while we're riding waves. Theory only gets you so far. At some point you gotta build stuff and try it and refine it.

like
0
PlusOneShaper's picture
Joined: 03/19/2004

@Oneula-

"Eh brah, what you doing?,  you got the back fin on backwards brah!"

I brushed it off with a smile and acted like I did it on purpose (being the mad surf scientist and all) but I felt like an idiot."

HA Bernie!  Totally relate, quite the mental picture, funny how it worked that way though! 

@mattwho-

Well Matty, I think you're right, I'm the first guy in the Hotseat (or so I'm told,) so every day done, is a record, ha!!!

"Very aware of entry rocker and flow thru both double and singles.  If I may can you give us you astute opinion?"

Probably the best thing is to NOT look at the concaves.  Maurice has it down: "Look at the rockers mate..."  The rocker down the stringer is LESS than the rocker along the rail. The by-product is concave.  I am of the opinion that your have to look at the rockers before any "dent" or feature, plus there are advantages to look at the rockers NOT parallel with the stringer, thus adding a lateral component to the water flow direction.  Also, consider what more rocker at the rail offers...  ...especially in a hard turn (dipping your rail.)  If you are travelling in an arc, and you are on a curved (moving) surface, "Do you think the fastest rocker is going to be FLAT?"  Snowboard and Ski Designers would say "NO!" (and powder doesn't move like waves do against our boards...)  More food for thought.

@offshore-

Yes!  Learned a lot.  We used that South African "Four Way Fin System" I mentioned a couple hundred miles ago, ha, which allows the fin to be moved (four ways.)  Fore/aft, Toe (pointing toward/away from nose,) Camber/Splay (tilting tips away from stringer,) and of course changing the fin itself.

Like I said we learned a lot, and it turned out the fins felt best Splayed 5-7 degrees for thruster side fins, and 3-4 degrees for quad rears.  BUT, that said, you can get very good results OUTSIDE those findings, especially with super deep concaves, where you might like 2-3 degrees, or not.  OH, also, those numbers are based upon "flat bottoms" as a Vee or Concave will change the Camber/Splay quite a bit.

@Artz-

I alluded to that topic early in this thread.  If I had unlimited resources I would use FEA (computer modeling of dynamic flow and self-optimization,) and I would create a "shape shifting surfboard."  It would be great to paddle into a wave with a beefy board, then once I got going, shrink it down to Tow In size, or even Skim Board size! ha.  Also mentioned was 3D Printing, which I can assure you is going to happen (might want to get proficient at basic computer modelling of surfboards the way we can now look at a blank catalog and "know" which blank is "right,") thus, you can get a Very Close Tolerance blank with variable density, controlled flex, and controlled weight distribution (without any wastage.)

@shapaholic2011-

Yeah, I don't think he's opposed to anybody making a short, wide, two-finned board that's a lot of fun, ha!  That was more for the lineage, for being the one who specifically studied and restored a real Simmons board a long time local surfer here named John Elwell had for decades, then being consigned to make the "Mini" version of it, and being able to sell boards literally under that name.  It's sorta like saying "Make a photocopy of this,"  vs. "Make a Xerox of this," but only amongst us surf folk... ha

Best regards,

George

like
0
lemat's picture
Joined: 04/17/2010

Artz, It´s a cost and look problem. Airplane composits parts are not so advanced infact, most are foam or nida core cover with carbon epoxy. The way to design and product composits parts progress. Stronger surfboards are made know (compsand with foam,wood, or exotic fibers skins) but they cost more and for most don't look like the pupe of pro surfer. On industry point of view, If surfers are ok to change board each years or less, why change.

like
0
shapaholic2011's picture
Joined: 01/04/2011
George - sorry for late reply back. Anyway, I don't plan to name my board " mini simmons " after what you said. On a side note, I think -Joe Baugeus definitely designed his own model. I mean, look at all the copies. Not many of Them are built as -Joe describes in his vimeo vid. That there proves he "IS" the founder of his unique Mini Sims boards. I think he deserves that respect. Sadly, a lot of Folk's don't give him the respect he deserves!-Jim
like
4

"Freestyle."

PlusOneShaper's picture
Joined: 03/19/2004

@Lemat-

"Artz, It´s a cost and look problem."

So true, Lemat, and very sad, that fashion runs what sells to surfers.  And there were times when it wasn't so, then there were times before that were it was true again...

(looking at the late 60's and the early 60's as an example.)  Wondering what part of "the cycle" we are in now?  Looks like we are breaking free again, as more innovation seems to be surfacing, yet in the midst of the innnovations emerges mass-marketed efforts (without naming names.)

@shapaholic-

Hi Jim, I definitely acknowledge that negative vibe, he drew fire from many directions.  I've gotten to know Joe quite well at a personal level, and we've talked for hours about his upbringing and background- and 50+ years of shaping.  He has some of the coolest stories about growing up in that period of Surfing/Chicks/Hotrods in SoCal.  He was right in the middle of it all, amazing man, strong principles and very conscientious of the quality of his work.  INSANELY precise with a planer, and amazing stamina shaping some of the most beastly EPS blocks I've seen.  I wished he'd come on here and talk design, as the latest mutation of his Mini Simmons with radical bottom contours looks incredible! He's not one to sit still with his shapes and ideas...

Best regards,

George

like
1
shapaholic2011's picture
Joined: 01/04/2011
+2 George! Yeah, it would be cool if he visits swayz and Maybe offer a few tips. Damn, talkin about planing... im probably average planing flats, but slow n low for me on everything else as I recently bought a-- 7.5 AMP SKIL100! It's a beast. But purs like a big cat! Today I cut in nose/ tail rocker w rocker templates for first time. It's going! Anyhow, I plan to try my first single to dub concaves. Any tips would help. I am just try n to figure out where to halt my single so it works w dub concaves. Think n of try n what Joe Bageuss does on his mini. I think he lets the double carry out back? Will this mimic vee? Tia for any help. Best regards. Ps: if you ever visit Monterey bay area -I'm making a tester board I'd like Folk's to try out. This is -- the test model! The " Screwdriver 6' x 19 1/2" rounded square tail! I didn't know what to shape - so I just am going by feel..my nose rocker is a bit tight....I might have cut too much nose off. Or I miscalulated thickness of the blanks nose...might have to thin it more? Gonna put two fins about 6" or so up the tail block.... might put em 1 1/4"-1/2" off rails? The cant I think maybe slight? I'm not sure how I want it yet? I just want it drivey and have a lively feel....Don't we all.......! Rails I'm still thinking about?T c-Jim
like
3

"Freestyle."

johnmellor's picture
Joined: 03/17/2004

Hi George - Just a quick note of thanks for posting so much information.  It all makes sense the way you put it.

like
0
GregTate's picture
Joined: 03/18/2004

Yes, thank you George. Great thread. You have been very generous with your time and information. We are in your debt. 

like
0

Personally I'm always ready to learn, although I do not always like being taught. - Winston Churchill

PlusOneShaper's picture
Joined: 03/19/2004

Got some very good news just now, Maverick's was bombing today and the 10'6" worked unreal today. Stoked!

@shapaholic2011-

Some tips for hitting the flats is to keep the back arm a bit tense, focusing on keeping the handle upright/vertical.  I have the front hand draped over the handle, sometimes brushing the work surface, much more relaxed.  I see a lot of guys doing the opposite, driving the front hand hard "into" the blank, which makes the planer "swim" around and climb out of its' intended track.  Once I get the bottom roughed, I set the cut for 1/16" or less (called a "flycut") and run along the bottom while focusing on good body position. It turns out that body position is SUPER IMPORTANT, also your stance, and WALKING with the planer.  Walk like a cat. ha.  

On your rail bands, pay attention to the rear handle, being sure it holds a constant angle (so the band surface doesn't "twist") throughout the entire pass.  Later on, you will use more advanced moves but mastery of consistent placement and awareness of the tool is essential, or you will not progress very far (I've seen some long time shapers who never pushed themselves with good technique, and it shows, the finished product is nice but it will look like they "go to pieces" as they make their way to that point plus it takes a LOT longer to correct stuff.)

I'm not a huge fan of "single to doubles" (although the Mav's board I just did is a sort-of InVee version of that,) rather I prefer "single with doubles" in a short wide board like you are doing there.  Try to use the planer as much as possible, but approach your cuts with a gradual actions when it comes to contours.  There are tricks to "tipping" the shoe of the planer into the concave but only attempt once you have the control of the tool position/angle pretty down pat. The Mini Simmons has doubles through the fins but they fade out at the tail block, althoug some of Joe's recent work has pretty radical contours flaring right off the tail (he has a special rolling pin grit tool to do them.)

On the Screwdriver board, not knowing the rocker, bottom contour, fin base length and some other details it is hard for me to say where a good place is for the fins.  Just guessing I'd say more than 6" and the 1-1/4" seems a little close to the rail.  Maybe expand on the details and I can further comment?

@johnmellor-

Hi John,

Not sure if you heard, but one day my friend Craig Klein walks into the shop and I have the Asymmetric board you sent, sitting front and center on a stand.  He always being interested in alternative designs, I tell him "John Mellor sent it" and he freaks out.  It was a classic moment!  You guys knew each other for decades, ha!  Small world...  Your board gets seen by many people!  Thanks again!

@gregtate-

"Runnin' up quite a tab there Greg..."  HA! I kid...  It's not a super HOT seat, actually it's been fun.  How long does this run for?  Do I just go away?

Best regards,

George

like
0
Huck's picture
Joined: 12/07/2009

PlusOneShaper wrote:

@greggriffin & @lawless-

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.  

Bill Thrailkill hasn't commented, but I thought he might be one of the shapers who have keyed in on this.  Makes sense to me, doesn't logically seem the foil in a fin could be giving comparable lift to the airfoil in an airplane wing, when the ratio of foiled area (fin) to the overall size of the vehicle (surfboard) is so much less than an airplane wing to the airplane - but the dymanic lift from water flow hitting the side of the fin seems a much more logical source of lift, like the freeway hand out the window example given.

It also (seems to me) explains why Bill's "twingle fins" work with the flat sides out, and the foil inside.  The flat sides provide the dynamic lift from water flow from either side, and the foil merely provides the streamlining, not the lift.

PlusOneShaper wrote:

@Huck-

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.

OK, its your thread, but I sure hope others don't take such a hardline view of general discussion.  Posting pics of current work is in no way a violation of any policy, and IMO could not be considered "selling wares" if done in the context of sharing / discussing design.   And for those (like me) who don't do facebook, its a great chance for us to see some stuff we might otherwise miss.

Thanks again for a great thread.

like
0
shapaholic2011's picture
Joined: 01/04/2011
Thanks - George! I'll take notes! You are spot on - on fin placement tips also! I was thinking about it, but it's great to get help from a seasoned shaper! About planing: I think you're right about getting a grip on basic techniques b4 jumping up... this planer is a 7.5 amp beast and I'm starting to realize that.... one can't tell - til you hit 3/32" on up! Then you hear it growl n scream.....I set her back down to an 1/16 " to 3/32" if I have to mow out foam out in an area....then fade from there.... gotta lay that bed down right tho! You are sooo right. Ty and keep up the hand shaping! I'll do the same. I think if more Folk's step away from cnc, I think, we can keep hand shaping alive....too bad skil tools quit making the-- Skil 100. I wrote em and told em they dropped the ball. Tc - Jim
like
6

"Freestyle."

shapaholic2011's picture
Joined: 01/04/2011
George - the Screwdriver is basically a board for small to average head high + a bit more... the boards going to be a twin fin, but I was thinking oabout tossing on four boxes off rail the same distance off rail so I can ride it as a twin or a quad? Debating. For my iffy glasaing skills I'll prob glass on twins... gonna use a med raked set of twin fins I got at rainbow fins warehouse back in the nineties when I started shaping again.just a garage guy having fun.:) fyi - I carved out a bit more foam between fins...I saw a vid where a Shaper suggested that. Makes sense. It's a lever of sorts. Maybe a sweet spot. If I use 4 notches otf , well I hit it on #4 briefly.....to cut 0ut that area...then I faded out to zero up the board... did one clean up pass at 1/8" on the entire bottom. Gotta blend out the humps where I cut in rocker I think... there's a hump. My nose rocker is a little lower than I thought. So I'm taking another 1/16" or so off tip area - around 6"down my nose flip...gotta take some foam off deck/ tail area as my blank is a older Clark Foam blank. What do you think of a plain single concave? I'm thinking about it? Upfront, the single I was thinking about doin would start 8" in front of wp and gradually fattening to fins., And the dubs would carry out the tail. But I could flatten it out the tail block? For my concaves I just use a surform and block. Might dig out a straight pass w planer to get my depth using otf.... but I gotta be careful as I haven't ever cut a concave w planer yet. I like surform n to start dubs. It's just scrubbin an imaginary straight line between the fins & stringer! Then I kinda dig it out w surform and cross sanding w block...but I kinda screwed up sorta by not using anything about checking depth...did use a straight edge, but not enough. I saw Stretch on a vid use a pencil to check depth for concave. That is cool! I thought of stacking pennies :D. ! I think it should work. Thanks again for the help!:-) Ty - I'll do single first - then put doubles in... My stance is semi bent legs tripping around the coord almost! :D walk in like a smooth cat makes sense! It's coming along tho! It took me three mins until I felt I had ny game on...cranked up the beast and let her rip! We ( me & my old surf buddie) were cutting blank off the tail end to catch the rocker n nose...but! It kinda pushes apex behind center I found... so my thickness is back a bit- which seems to work. I'm glad I remembered bcuz I ran into him while check n the surf back n 83 or 84? My rider - Dane - a 14 yr old kid had me dropping my jaw no bull....he was a " stand out " amongst 5 other people out ....I walked up to him and he was the buyer of my board.anyhow, I told him I shaped it, and he said, " you gotta make more!" So that's why I'm shaping again. Thickness will be 2 3/4" on -- the SCREWDRIVER.
like
5

"Freestyle."

Pages