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Do concaves work? #2906341
01/31/19 01:10 AM
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DublAK2 Offline OP
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I've been doing a bit of research because I'm seriously considering shaping a board myself.

I've read some simple articles and perused through the swaylocks archives but nothing is really selling me that concaves aren't just a bunch of marketing BS.

What do you folks think? Can you really tell a difference? And if so are there any admirable characteristics of a flat bottom?

Re: Do concaves work? [Re: DublAK2] #2906343
01/31/19 01:14 AM
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Paging GG...


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Re: Do concaves work? [Re: DublAK2] #2906353
01/31/19 01:39 AM
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Everything works

A lot depends on your style , boards outline / rocker / fin position and what kind of waves you are surfing

So lets say you are surfing head high Rincon on a low volume hpsb, a nice amount of rocker plus single concave will work very well . same exact board with a flat bottom nose to tail might not have as nice of feel .

Now get a wider outline , lower rocker and higher volume board with flat bottom . it will feel fast and skatey

Re: Do concaves work? [Re: DublAK2] #2906358
01/31/19 01:53 AM
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If you dont think they work try a Bonzer concave and then get back to me.

Last edited by surfy1476; 01/31/19 01:54 AM.
Re: Do concaves work? [Re: DublAK2] #2906360
01/31/19 01:59 AM
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well the whole top 44 is riding concaves, i'll go with yes

Re: Do concaves work? [Re: DublAK2] #2906363
01/31/19 02:02 AM
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They work, but not how you think they work.

They make the rocker flatter where they are deepest, so it makes the board faster.

Re: Do concaves work? [Re: DublAK2] #2906374
01/31/19 02:31 AM
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If this is your first board and you plan on glassing it yourself. Go with flat or vee and you'll have less to worry about during the lam and sanding. KIS should be your focus on board number 1

I don't think you can separate one component of a design from another like the debate of flat versus concave versus vee versus domed. outline rail rocker fin setup and materials all play a part in as much as the bottom contour.

The only case where this can be done is when some say red boards are faster.
I think color is probably the one component of a surfboard that can be isolated from the rest of a design.

But then you never know the effect of pigments to the resin/cloth/foam bond. Does anyone really understand the impact of pigment to the chemical nature of a resin and its hardener. Kind of like using heavy pigments with UV resins.


Last edited by oneula; 01/31/19 02:34 AM.

waSUPcuz? shaka ala n da mooleh bulls..
Re: Do concaves work? [Re: DublAK2] #2906404
01/31/19 04:08 AM
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Yes concaves work for performance shortboards. Look at any picture of a surfer in a bottom turn or cut back you'll see the water moving diagonally across the bottom of the board. If you lay a straight edge at a diagonal on a concaved bottom - you'll see the edge lays flat i.e the shortest line - the fast surface for water to move across on the unweighted side during a turn. Concave provides lift but also allows a curvy rail line which turns easier.

If you're nervous about creating concave. You can make a rig. After the blank is fully shaped. Get a strip of ply say 3- 4 mm thick, about 100 mm wide and slightly longer than your board width, glue 150 grit sand paper to it. Attach a handle of some sort to the centre of the plywood - at right angles to the long edge.

Get two long strips of wood (about 2 ft longer than your blank) say 10 mm thick. Lay either side of the stringer. far enough apart to run a router bit between them. Weight the ends so the wood conforms to the bottom curve. Now chock the ends to be the depth of the concave at it either end. The idea is to create a smooth guide for you router to cut deepest at the deepest point of your concave and fade to zero at the chocked points. Set router depth to concave depth - say 5 mm. After cutting a groove down the middle of the board, you use the plywood sanding block in long strokes to bring the foam down to the stringer. The ply will bend giving you a nice concave profile curve. Tape the rails if you're worried about cutting into the rail line.

Last edited by Spinafex; 01/31/19 04:09 AM.
Re: Do concaves work? [Re: DublAK2] #2906416
01/31/19 04:29 AM
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dont over think it, if this is your first board it's most likely not going to come out exactly like you imagine.

so at this point, just have the balls and go for it concaves or not.

be a player and get high on the action.

add water and enjoy!

calling grandpa griff to the suction cup.


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Re: Do concaves work? [Re: DublAK2] #2906424
01/31/19 04:53 AM
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Ride a flat board, and then ride a DEEP concaved board like a Maurice Cole. You'll feel it. I'm on the fence still about the very deep concave's like Cole's; I've had both excellent and meh results with them. But at the same time one of my worst boards I've had was a flat bottom.

You should shape one flat, and one deep single and compare the two. Then build off those; lessen the depth, double concave, vee, ect.

Bottom contours weren't made arbitrarily or as a marketing gimmick.

Re: Do concaves work? [Re: manbearpig] #2906434
01/31/19 05:10 AM
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Originally Posted By: manbearpig
Ride a flat board, and then ride a DEEP concaved board like a Maurice Cole. You'll feel it. I'm on the fence still about the very deep concave's like Cole's; I've had both excellent and meh results with them. But at the same time one of my worst boards I've had was a flat bottom.

You should shape one flat, and one deep single and compare the two. Then build off those; lessen the depth, double concave, vee, ect.

Bottom contours weren't made arbitrarily or as a marketing gimmick.


my MC:


my deep single (right two):



Now, I'm on a flat bottom. Not much difference.


Organized competition is entirely peripheral to surfing qua surfing. People surf for love. - William Finnegan
Re: Do concaves work? [Re: ghostshaper] #2906435
01/31/19 05:14 AM
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Re: Do concaves work? [Re: ghostshaper] #2906438
01/31/19 05:18 AM
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Originally Posted By: ghostshaper
Originally Posted By: manbearpig
Ride a flat board, and then ride a DEEP concaved board like a Maurice Cole. You'll feel it. I'm on the fence still about the very deep concave's like Cole's; I've had both excellent and meh results with them. But at the same time one of my worst boards I've had was a flat bottom.

You should shape one flat, and one deep single and compare the two. Then build off those; lessen the depth, double concave, vee, ect.

Bottom contours weren't made arbitrarily or as a marketing gimmick.


my MC:


my deep single (right two):



Now, I'm on a flat bottom. Not much difference.


Whoa bro when did you get corked? Did I miss that somehow?

I have boards with all sort of varying concaves. They all work.


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Re: Do concaves work? [Re: silentbutdeadly] #2906445
01/31/19 05:23 AM
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6-7 years ago, when I was still on my quad trip.


Organized competition is entirely peripheral to surfing qua surfing. People surf for love. - William Finnegan
Re: Do concaves work? [Re: ghostshaper] #2906467
01/31/19 06:05 AM
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Originally Posted By: ghostshaper
Originally Posted By: manbearpig
Ride a flat board, and then ride a DEEP concaved board like a Maurice Cole. You'll feel it. I'm on the fence still about the very deep concave's like Cole's; I've had both excellent and meh results with them. But at the same time one of my worst boards I've had was a flat bottom.

You should shape one flat, and one deep single and compare the two. Then build off those; lessen the depth, double concave, vee, ect.

Bottom contours weren't made arbitrarily or as a marketing gimmick.


my MC:


my deep single (right two):



Now, I'm on a flat bottom. Not much difference.

Boards look killer. Looking similar to a few boards I was given to ride for a week or so by a shaper in AUS when I lived there, blanking on the name. Do you wax those?

I do prefer concave's over flatter. But I think it really comes down to the board design and waves intended for how much depth you want on the concave's.

Re: Do concaves work? [Re: DublAK2] #2906490
01/31/19 07:00 AM
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It works in different ways depending on your position in the wave. Webber gives a good description on how concaves can give more hold in the turn in his description of the creature. But as racer1 said above, traversing the wave it could improve speed since it takes out rocker reducing drag on the half that is sitting in the water. If the board is flat on the wave you can get some lift since an air pocket forms underneath sort of like a catamaran. I like the spoon analogy, run water and place a spoon under the faucet, then feel what concave does by redirecting water flow. Also read up on edge board design, its interesting how the contours can provide lift and drag in some cases. Tomo did something pretty cool with the noses on the vanguard/vader models, where there is a slight double vee at the nose so when you turn off the nose it does give some lift like and edge board would. Try shaping hand planes first and use a water hose to test out how they might feel. To me this is the coolest thing about custom shapes, otherwise if you want a flat board then just get one at costco, no sense in spending time and money shaping something boring.

Re: Do concaves work? [Re: Spinafex] #2906608
01/31/19 03:17 PM
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Thanks for the rig suggestion Spinafex! Thanks for the encouragement Oak!

I don't plan to glass this one. I figured I should work on botching one discipline at a time.

I'm not trying to shortcut my board by skipping concaves. I'm just questioning the efficacy of concaves. I have an old Michael Barron 6'4 with a flat bottom from when I was a little guy learning 20 years ago. I always kept it around for nostalgia, but it's also fun to ride still every now and then. It's really long and skinny which was the style in the 90s but the rockers are relatively flat for the era so it still works. Anywho, for the life of me I cannot feel a "lack" of concave when I ride it. It actually feels pretty fast, just a lot of board in front of my front foot. It still turns too, just takes a longer wind up to whip the length around.


Since GG seems to be busy can anyone venture to guess what he would say?

Re: Do concaves work? [Re: DublAK2] #2906716
01/31/19 05:29 PM
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My feelings are that concaves help provide an edge when it comes to instant acceleration, but not necessarily top end speed.

I've found that in smaller, less powerful waves I enjoy a board with a fairly curvy rail line and a deeper concave. This keeps the center line rocker flat for speed while the rail is curved enough to fit tight turns when needed. As the waves get more powerful, the concave can get shallower. It's not as critical since the wave is supplying you with plenty of power for that acceleration.


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Re: Do concaves work? [Re: DublAK2] #2906994
01/31/19 11:02 PM
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As an experiment about 10 years ago I made myself two shortboards that were identical except one had an 80s V bottom and the other was a single to double concave with some V out the tail. Both boards worked fine but the V bottom board felt better under my feet.


This is a bad day for the news media. Lets not kid ourselves, Toobin said on CNN. The larger message that a lot of people are going to take from this story is that the news media are a bunch of leftist liars who are dying to get the president, and theyre willing to lie to do it.
Re: Do concaves work? [Re: DublAK2] #2907013
01/31/19 11:49 PM
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One of my boards has a Vee in the nose to double concave and flat out the back. I noticed a really cool sensation on a late steep drop in when setting the board on rail, it did feel smoother around the nose like a little bit of slide helped the board settle first before the concave around the middle hooked in. Stretch guns typically have a vee in the nose too. I haven't tried the Hayden Shapes Psychadelic germ, but it's contours look super interesting next level design with a displacement hull nose to double concave and vee out the back.

Re: Do concaves work? [Re: DublAK2] #2907409
02/01/19 09:44 PM
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How do the cork decks hold up over time?

Re: Do concaves work? [Re: jkb] #2907417
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Originally Posted By: jkb

I've found that in smaller, less powerful waves I enjoy a board with a fairly curvy rail line and a deeper concave. This keeps the center line rocker flat for speed while the rail is curved enough to fit tight turns when needed. As the waves get more powerful, the concave can get shallower. It's not as critical since the wave is supplying you with plenty of power for that acceleration.


...and this kind of observation is what confuses me and leads me to doubt their utility. Through perusing Swaylocks I've read Mike Daniels from Coil speak about how he doesn't use concaves on very low rocker boards, and boards over 21" wide. He don't recall if he gave any reasoning.


So you like concave on grovelers and he does not

Re: Do concaves work? [Re: DublAK2] #2907422
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I have the same opinion. In fatter waves, less concave is needed because the board has less rocker. For steeper waves and more rocker, more concave to reduce the rocker in the middle so there is less drag there while traversing the wave, but maintaining rocker in the rails for ease of turning and late drop ins. What I try to do is visualize where the board will drag and at what angles, more wetted distance/surface area is more drag, so adding a concave can cause drag if that part of the board is in the water since the length to the rail is longer. If an air pocket forms, then you have less drag, but you need more speed to get an air pocket to form.

There are quite allot of details about concaves described in the Greenlight surfboard design guide. Also there is a pretty cool video from Firewire working with Red simulations where they model board shapes and create heat maps showing where pressure builds up, pressure is drag. I've thought about learning SolidWorks and using their Flow simulator for the same reason, but that is pretty hard to do and expensive for a hobby.

https://youtu.be/-cgFb-DKFfc

Re: Do concaves work? [Re: DublAK2] #2907594
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The simplest machine is the best machine.

Re: Do concaves work? [Re: DublAK2] #2907675
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Originally Posted By: DublAK2
Originally Posted By: jkb

I've found that in smaller, less powerful waves I enjoy a board with a fairly curvy rail line and a deeper concave. This keeps the center line rocker flat for speed while the rail is curved enough to fit tight turns when needed. As the waves get more powerful, the concave can get shallower. It's not as critical since the wave is supplying you with plenty of power for that acceleration.


...and this kind of observation is what confuses me and leads me to doubt their utility. Through perusing Swaylocks I've read Mike Daniels from Coil speak about how he doesn't use concaves on very low rocker boards, and boards over 21" wide. He don't recall if he gave any reasoning.


So you like concave on grovelers and he does not


My groveler rocker isn't low if you measure rocker along the rail line. The rail rocker is continuous and curvy. Nothing extreme, but there's some curve to it. This helps with tighter turns on small waves where the pockets or the area in which you have to complete a turn is also small. I like a deeper concave in this situation because it flattens out the centerline rocker for speed.

If I had a board with a lower rail rocker to begin with, I imagine a shallower concave would work just fine, like what Mike Daniels is talking about. For me though, with that lower rail rocker, I'm not sure I would like the way it fits into a small pockety wave.

I still think concaves help with instant acceleration, but that's just a hunch. I could be wrong.


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Re: Do concaves work? [Re: oakfoils] #2907730
02/02/19 11:57 PM
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Originally Posted By: oakfoils


calling grandpa griff to the suction cup.


Nobody likes suction


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Re: Do concaves work? [Re: DublAK2] #2907760
02/03/19 12:45 AM
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stuff to read while I'm bored


https://greenlightsurfsupply.com/pages/surfboard-design-guide :

"water will encounter resistance against the aft section of the concave, creating a force against the downturned rail edge which pushes not only up (lift), but back and out as well, inducing a degree of drag. But this phenomenon is what gives some riders a sense bite or added hold in steep faces or hard turns."

lots of experts, at least Greenlight mention of the complexity of the concepts and posts generally excepted ideas. imo

Last edited by need 4 speed; 02/03/19 02:19 AM. Reason: forgot imo

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Re: Do concaves work? [Re: need 4 speed] #2907767
02/03/19 01:10 AM
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Every single one of my favorite boards has had a single t
o double concave bottom,
with several variations. I hate thrusters, only quads, twinzers, twins, or twin/trailer for me.
So yes, they work very well.
But, opinions are like....


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Re: Do concaves work? [Re: Oceanslide] #2907787
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Right now I'm on a :very subtle single to vee trip
I think I get a long better with nothing too drastic
I doubt if i could tell the difference if things weren't too dramatically different
(single,single to double, spiral vee)

cheers


NOT THAT KIND
Re: Do concaves work? [Re: NinjaPete] #2908288
02/04/19 10:59 AM
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If you want to understand how concaves work - check this link:

https://www.cambersurfboards.com/built-from-science

Theory based on empirical observation

Re: Do concaves work? [Re: Spinafex] #2908292
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A flat bottom board, or even a board with a conventional shallow concave, allows increased flow to escape off the rails resulting in lower pressure under the board. The goal is to increase the pressure on the bottom of the board to increase lift. More lift allows the board to carry the weight of the rider with less drag. Less drag lets you go faster

Flat bottom allows increased flow to escape off the rails resulting in lower pressure under the board.

This is release enabling everything you could want - lower drag too


Re: Do concaves work? [Re: Greg Griffin] #2908357
02/04/19 04:33 PM
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Originally Posted By: Greg Griffin
A flat bottom board, or even a board with a conventional shallow concave, allows increased flow to escape off the rails resulting in lower pressure under the board. The goal is to increase the pressure on the bottom of the board to increase lift. More lift allows the board to carry the weight of the rider with less drag. Less drag lets you go faster

Flat bottom allows increased flow to escape off the rails resulting in lower pressure under the board.

This is release enabling everything you could want - lower drag too



Isn't the purpose of concaves to subtly redirect water, forcing more water into/over a certain area of the bottom thus increasing the speed of the water, thus creating lift? Good ol' Bernoulli?

Well, don't ask me. I don't pretend to know. All the study I've done of hydrodynamics came from reading books on yacht design (truly scientific volumes on surfboard hydrodynamics do not exist as far as I know). Sailboats are working in a much more steady state environment. Surfboards work in such a dynamic environment, with the speed and direction of water changing so rapidly and displacement (weight) constantly shifting,at times weightelss, at times loaded up, sometimes forward, sometimes further back, that it seems impossible to design with truly applied hydrodynamic theories in mind.

I didn't buy it when Tomo was spouting hydrodynamic theories. He was using Bernoulli to defend his use of concaves and his outlines. OK. No doubt his boards work and he a phenomenal test rider, but to say you understand exactly how those hydrodynamic forces are working on a surfboard and you can tweak your design in response is a stretch IMHO.

Wouldn't it be much more honest to say that test rider feedback and years of iterative design has shown that flat bottoms (for Griffin) or concaves (for Tomo) work?

I like flat bottoms. I consider them neutral. However in certain situations bonzers (single to double) have blown my mind. Once in a while, when the stars are aligned just right, I'll do a cutback on my bonzer that feels like you hit the throttle halfway through and you gain speed in the turn (the legendary "fifth gear"). But even the Campbells used the term "venturi effect" to describe their boards. But Bernoulli's classic experiment was with water flowing through a closed tube. Wouldn't water flowing over the bottom of a surfboard, encountering a concave will seek the path of least resistance which, seems to me, is to move downward away from the board. Or am I missing something here?

Anyways, let's hear your explanations. Always fascinating stuff.

Re: Do concaves work? [Re: patrolman] #2908384
02/04/19 05:10 PM
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GG. Sorry man didn't understand your post. Do flat bottoms or concave bottoms create less drag? I was confused about which one u were speaking to.


I'm going to attempt a groveler. I'm thinking about splitting the difference and making a super shallow single concave. something less than 1/8". Of course, execution of the plan will be a crapshoot.

What feeling am I trying to achieve with a super shallow single? Not an effin clue! If I can stand on it I'll consider it a success.


Always fun to talk surfboard design though and act like my DIY project will work

Re: Do concaves work? [Re: DublAK2] #2908428
02/04/19 06:03 PM
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I copied the article .

Re: Do concaves work? [Re: laidback] #2908441
02/04/19 06:33 PM
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Originally Posted By: laidback
Originally Posted By: oakfoils


calling grandpa griff to the suction cup.


Nobody likes suction


oh contraire, hint; all majority of the modern hpsb commmon design element is the control and release of suction.

everybody riding one likes one even if they realize it or not.

all things work to some degree, knowing when to stop is the key.


Oak Foils Customs Keep Kustom Kulture Alive!
Re: Do concaves work? [Re: oakfoils] #2908587
02/04/19 10:03 PM
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Some of these articles say the downturned lip on the rail created by the concave is similar to a long fin .

Fins are toed in , this lip is toed outward by following the tail template .

Imagine what happens when you do this with your fins .

Re: Do concaves work? [Re: DublAK2] #2908594
02/04/19 10:19 PM
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Tomo's designs are based on real math. Maybe initially he came up with his designs based on experiments and theories in the past done by others, but later Firewire worked with him and did some hard math. There is an article about it on their website. You can clearly see the effect of concaves in the heat maps, they describe in great detail the effect of hard vs. soft rails in the video, the importance of rocker et... It would be awesome if board designers gave this kind of detail to the customers for all of their board designs.

https://firewiresurfboards.com/the-wire/...ard-performance

Re: Do concaves work? [Re: NinjaPete] #2908745
02/05/19 02:57 AM
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Several ass backwards statements in that Video .

I like Tomo's quad concave bottoms , just not inset in a concave , but like those done in the 70's .

Re: Do concaves work? [Re: DublAK2] #2908804
02/05/19 05:54 AM
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The video is a hasty summary of what is going on. I wish they would have went into more details as to why the Omni is faster than the Vader in more critical wave conditions. I like the sequoia website how they give details on drag numbers and lift for a given model. That way the customer can weigh the pro and cons of wanting more lift/drag for mushy waves vs flat out speed in critical waves. https://www.sequoiasurfboards.com/en/cfd

Re: Do concaves work? [Re: NinjaPete] #2908831
02/05/19 11:31 AM
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If the turned down rail creates lift to the point you adjust the size of the board due to the additional support , it would fly out of the water at higher speeds and larger waves .

Pipeline , Off the Wall , J Bay etc .

I have no problems with concaves - big problems with the descriptions of what they do and how they do it .

Re: Do concaves work? [Re: NinjaPete] #2911377
02/10/19 06:16 AM
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Originally Posted By: NinjaPete
Tomo's designs are based on real math. Maybe initially he came up with his designs based on experiments and theories in the past done by others, but later Firewire worked with him and did some hard math. There is an article about it on their website. You can clearly see the effect of concaves in the heat maps, they describe in great detail the effect of hard vs. soft rails in the video, the importance of rocker et... It would be awesome if board designers gave this kind of detail to the customers for all of their board designs.

https://firewiresurfboards.com/the-wire/...ard-performance


I'm still not buying it. Real math? Heat maps?

I could be totally wrong but someone will have to convince me.



In this photo he is indicating a path around the rail that would be perpendicular to the board. Water is never wrapping around the rail in the direction he indicates. It is moving nose to tail and so the profile it would be wrapping around would be a slice parallel to or maybe 20-30 degrees off the stringer. And for sure, no water would be moving in the direction of the little arrows, perpendicular to the bottom of the board. Overlooking this fact, and taking about water movng the way he indicates, to me indicates BS. It is ignoring how water is really moving.

In yacht design you have "waterlines" which are horizontal sections, "buttocks" (yes I said buttocks) which are vertical sections, and "diagonals" which are, obviously, diagonal sections. Those diagonal sections are really important because that is the path water will moving when the boat is heeled which is almost always. It's good to keep in mind how the water is moving.






My first reaction to this photo was "How do they get pressure readings from a photograph?" Heat maps? shrug Also, what we are looking at is a backside top turn. I find it hard to believe that the rail that is being buried is the low pressure zone and that the separation zone, where water is leaving the bottom of the board (the beginning of the spray) is the high pressure zone.






In this part of the video it keeps showing "splashes" of water directed forward. When has anyone ever seen water being thrown forward while surfing? This leads me to doubt the validity of the whole model.






Finally, in this photo it shows standard rocker having low pressure across the length of the bottom, whereas the lower rocker board has higher pressure across the bottom (the two different boards are combined in a composite in this image). The presumption here is that low pressure is release and therefore faster, whereas the lower rockered board with all that high pressure would be slower. Since when has board with less tail rocker (all other things being equal) been slower?


So again, when I'm confronted by someone or some company trying to use "real math" to hype their boards I just don't buy it. I know they use CFD extensively in yacht design but the models the use are backed up with a lot of tank testing data and even then it doesn't always work. I don't think any tank testing (or wind tunnel testing, which is probably what this car designer uses to get his numbers) would accurately mimic the dynamic environment a surfboard operates in, so no, at this point in time I personally do not think CFD has any real practical application for surfboard design. Maybe as a marketing tactic. Maybein the future.

For now design,shape, glass, REAL WORLD testing and refine.

And in the end anything will surf, even a lunch tray or kitchen table. wave2



Re: Do concaves work? [Re: patrolman] #2911397
02/10/19 12:42 PM
02/10/19 12:42 PM
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I personally do not think CFD has any real practical application for surfboard design. Maybe as a marketing tactic. Maybein the future.

For now design,shape, glass, REAL WORLD testing and refine.

Excellent cheers

Re: Do concaves work? [Re: DublAK2] #2911493
02/10/19 06:19 PM
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my surfing improved when i went from flat bottoms to concaves

Re: Do concaves work? [Re: 000] #2911508
02/10/19 06:46 PM
02/10/19 06:46 PM
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Originally Posted By: 000
my surfing improved when i went from flat bottoms to concaves


Bingo!

Or, my board feels spicy and alive, and you can lay into a turn with five times the power, ooweee!

Funny that 99.267% of expert surfers don't feel that way. Oh wait...

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