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#2762499 - 03/13/18 05:05 AM Re: Flat vs. Concave [Re: paunch23]
Mr J Online   content
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Registered: 08/18/03
Posts: 734
Loc: Melbourne Australia
Originally Posted By: paunch23
"single concaves through the middle of a pro level surfer's board do nothing (regarding lift). if you were towed behind a speedboat at 40mph then yes the thing would probably lift... "

anyone hear this on surf splendor podcast? if not: http://surfsplendorpodcast.com/174-wax-on-dave-parmenter/

i asked at what speed does lift come into play and the answer was as you paddle in. so which is it? 40mph (going real fast) or paddling (going real slow).


Hi Paunch, I already answered your question on this thread in some detail - pasted below for convenience (extra info at end removed to get right to the answer).

However, you are asking for the actual numbers of the speed. That is going to vary for all sorts of reasons - curve of wave, weight of rider etc etc. So all we can do is estimate. Looking at my answer below we know that the board starts to plane at a speed that is faster than paddling, but less than maximum speed. What is maximum speed? Again depends, but for a ball park figure I taped a GPS to the nose of my surfboard and in well overhead waves at one of Vicco's premier point breaks the maximum speed was 36 km/h and I was consistently holding around 30 km/h on the waves I caught.

However, it is absolutely not necessary to have waves like that to get the board up on the plane - I would say it starts planing just before we pop to our feet and can do that going straight towards the beach, so unlike the speeds recorded above which were running with the shoulder we could take the wave speed of say a 2' wave in poor conditions as a guide.

from https://en.wikipedia.org/wiki/Wind_wave if a 0.9 ft wave from short fetch goes about 10 km/hr and a 5' wave short fetch goes about 20 km/hr

maybe about 15 km/hr? I dunno just a guess

Originally Posted By: Mr J
Originally Posted By: paunch23
At what speed does this lift come into play??


Definition of lift is an upward force. All surfboards generate lift regardless of whether they have flat, V'd, rolled or concaved bottoms. Otherwise they would head towards the bottom of the sea.

Lift can be explained in a number of ways using Newton's physics.
Flow turning and Eulers equations is one way. I like that way because it is intuitive enough for me to get my head around it. So if water hits the underneath of a surfboard at an oblique angle, it will get deflected or turned. At the point the water turns a force perpendicular to the radius of that turn will occur, so if water deflected downwards force will be upwards which is lift.

One of Eulers equations I found here d * v squared / R. Left side of equation is pressure difference perpendicular to flow which I think we can consider to be lift in our situation.

d is density, v is velocity and R is radius of turn. So not surprisingly the faster the flow the bigger the lift.

When a board is being paddled there is a fair amount of drag. There is some skin friction drag and notably there is a lot of form drag. Form drag is the ploughing effect of having to push water out of the way. On a short board the board is largely submerged and even the surfers body is partly submerged and has to push water.

So my answer to your question is that the lift comes into play when speed provides enough lift to raise the board enough to the point where a substantial drop in form drag occurs. At this point the board breaks free from its form drag and starts to plane.

...

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#2762501 - 03/13/18 06:46 AM Re: Flat vs. Concave [Re: caramel_Sea]
caramel_Sea Offline
Billy Hamilton status
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Registered: 05/29/08
Posts: 1708
The centerline is beyond flat: its inverted! And it slows the board down!

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#2762512 - 03/13/18 08:13 AM Re: Flat vs. Concave [Re: caramel_Sea]
GromsDad Online   content
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Registered: 01/21/14
Posts: 12177
Loc: 600 yards from the surf.
Where do V bottom boards come into the mix? Not very common to see these days but my experience has been that they surf good waves better than concave boards. They are more responsive and are much easier to do vertical turns on. Granted they aren't as good in mush and you aren't going to be busting airs on a V bottomed board but I do think many surfers would benefit from trying a board with a V bottom in punchy shoulder high and bigger surf.

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#2762861 - 03/13/18 05:02 PM Re: Flat vs. Concave [Re: GromsDad]
Duffy Online   content
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Registered: 04/27/16
Posts: 3290
Loc: Your moms house
Originally Posted By: GromsDad
Where do V bottom boards come into the mix? Not very common to see these days but my experience has been that they surf good waves better than concave boards. They are more responsive and are much easier to do vertical turns on. Granted they aren't as good in mush and you aren't going to be busting airs on a V bottomed board but I do think many surfers would benefit from trying a board with a V bottom in punchy shoulder high and bigger surf.


A little bird told me that when Kelly was winning world titles on Fred Rubble and Semi-Pro/(SP12) models they were flat (very slight single) under the front foot and vee out the back (starting just behind the front fins).

Dont know if thats true for all his boards at the time but Ive seen one that is made that way...
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#2762865 - 03/13/18 05:06 PM Re: Flat vs. Concave [Re: GromsDad]
surfy1476 Offline
Legend (inyourownmind)

Registered: 01/26/18
Posts: 185
Originally Posted By: GromsDad
Where do V bottom boards come into the mix? Not very common to see these days but my experience has been that they surf good waves better than concave boards. They are more responsive and are much easier to do vertical turns on. Granted they aren't as good in mush and you aren't going to be busting airs on a V bottomed board but I do think many surfers would benefit from trying a board with a V bottom in punchy shoulder high and bigger surf.


Vee bottom is amazing in lined up good surf, see Black Beauty.

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#2762968 - 03/13/18 08:02 PM Re: Flat vs. Concave [Re: surfy1476]
Duffy Online   content
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Registered: 04/27/16
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Loc: Your moms house
Originally Posted By: surfy1476
Originally Posted By: GromsDad
Where do V bottom boards come into the mix? Not very common to see these days but my experience has been that they surf good waves better than concave boards. They are more responsive and are much easier to do vertical turns on. Granted they aren't as good in mush and you aren't going to be busting airs on a V bottomed board but I do think many surfers would benefit from trying a board with a V bottom in punchy shoulder high and bigger surf.


Vee bottom is amazing in lined up good surf, see Black Beauty.


Yeah and those hard rails all the way nose to tail, yum.

Davey Smith made a few 6(+) fin boards with hard rails like that a couple years ago. Vee also (IIRC). Went really good...
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#2764334 - 03/16/18 12:24 PM Re: Flat vs. Concave [Re: caramel_Sea]
caramel_Sea Offline
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Registered: 05/29/08
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@ 1:53 in the video
"It's got a single concave channeling into a double between the fins, I don't know I just think it looks good."
Then rolls his eyes when he says "makes it turn like that! 'snaps'."
He knows it just looks cool and adds control
At least his is toed into the flow direction! Unlike the Machado boards.
I like Troy's boards btw, all good rockers, he will foil them out more with time

Elmore Surfboards - Frye'd Fish model from SEAKONG on Vimeo.


[vimeo]https://vimeo.com/257450873#t=113s[/vimeo]

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#2764535 - 03/16/18 07:23 PM Re: Flat vs. Concave [Re: caramel_Sea]
Havoc4k Online   content
Legend (inyourownmind)

Registered: 05/23/16
Posts: 397
Loc: in da hood next to paradise
Have two flat to double conc bottom boars on the way.
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#2777378 - 04/12/18 01:55 PM Re: Flat vs. Concave [Re: caramel_Sea]
chrisp510 Offline
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Registered: 12/01/08
Posts: 1634
"this has been my DD template for a while - in the past few years I've made this board about a dozen times, bunch of different bottoms, but I always come back to the single all the way out the tail. 5'4 x 18-1/2 x 2-1/4. I'm 145lb x 5'8"

I have recently made 3 boards (twinzers) with similar templates but different bottom contours. Drastically different ride characteristics. Which bottom configurations have you gone through on your twins and what are your thoughts on them?

Have you tried:
- Single to flat?
- Flat throughout?
- Single to double?
- Single to double with V off the tail?

Of the ones that I have tried,...

Single to flat was the best.

Single to double with V off the tail was good but I feel it lacks thrust when I pump. It goes way better than flat but not as good as single to flat.


Edited by chrisp510 (04/12/18 06:34 PM)

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#2777481 - 04/12/18 05:05 PM Re: Flat vs. Concave [Re: caramel_Sea]
GWS Offline
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Registered: 01/11/02
Posts: 41439
Loc: Somewhere else
Originally Posted By: caramel_Sea
@ 1:53 in the video
"It's got a single concave channeling into a double between the fins, I don't know I just think it looks good."
Then rolls his eyes when he says "makes it turn like that! 'snaps'."
He knows it just looks cool and adds control
At least his is toed into the flow direction! Unlike the Machado boards.
I like Troy's boards btw, all good rockers, he will foil them out more with time
<iframe src="https://player.vimeo.com/video/257450873" width="640" height="360" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe>
<p><a href="https://vimeo.com/257450873">Elmore Surfboards - Frye&#039;d Fish model</a> from <a href="https://vimeo.com/user9612530">SEAKONG</a> on <a href="https://vimeo.com">Vimeo</a>.</p>
[vimeo]https://vimeo.com/257450873#t=113s[/vimeo]


Fryed fish?

Is he a Skip protege?

He also has a "Russ Short style" Bonzer. rolleyes

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#2777504 - 04/12/18 05:57 PM Re: Flat vs. Concave [Re: caramel_Sea]
oneula Offline
Michael Peterson status
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Registered: 06/03/04
Posts: 2538
the earth is flat..
oh wait!

no, no
it's flat for sure
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#2777571 - 04/12/18 09:02 PM Re: Flat vs. Concave [Re: chrisp510]
Greg Griffin Offline
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Registered: 10/31/04
Posts: 17328
Loc: Palm Coast , Florida
Chris

Flat is Dead , better description is Neutral .

Not being sucked up and back by concaves - aka Lively

Releasing for unlimited forward movement .

Finely tuned fins with their placement creating another level of Lift , Plane and Release .

I can post Many videos showing concaves limiting the boards flow .

"Lively" too the point the tail pushes the nose in or just stops the board .

Flat bottoms release in all rearward directions .
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#2777613 - 04/12/18 09:56 PM Re: Flat vs. Concave [Re: caramel_Sea]
tenover Offline
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Registered: 01/17/03
Posts: 8302
Loc: Point Loma, CA
Nice Byzak!

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#2777621 - 04/12/18 10:14 PM Re: Flat vs. Concave [Re: caramel_Sea]
chrisp510 Offline
Billy Hamilton status
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Registered: 12/01/08
Posts: 1634
I edited my comment Greg. And deleted that part.

The board that feels dead I *thought* (my failing memory) was flat but I went out today and measured rockers and mapped the bottom contours on my last 3 boards and the "dead" board actually has some single. So, I made sure to edit my post.

Now armed with numbers, I am convinced that the dead board feels that way because it has the most nose rocker.
My favorite board has the least nose rocker.
Learning a lot!

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