bellyboard for BIG guy

What works and what doesn't. Share design ideas, references and contacts for paipo board builders.
soulglider
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Re: bellyboard for BIG guy

Unread post by soulglider » Mon Feb 09, 2015 10:27 am

just wondering? single concaves are fast and help a board track, right? double concaves help a board get looser, correct? is a concave board faster than a flat bottom? do double concaves loosen up a board more than just vee? why are boards made like this now? wouldnt the concaves really only help if the board was on flat water, say in a lake, a tank or ocean on a flat day? how do these things actually help a board on waves and wave faces that are ever changing? are boards designed this way because thats the contemporary norm? doesnt it have more to do with wave type? smaller waves, flatter bottoms? bigger waves, concaves for holding power? multiple boards seem to be the answer. unless big waves are all that are surfed?

the picture looks cool.
deathbedpaipo.blogspot.com

skiff
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Re: bellyboard for BIG guy

Unread post by skiff » Tue Feb 10, 2015 10:31 am

The double concaves are really just acting as 'twin engines' for these types of boards? Concaves generate LIFT, and often, lift generates speed. The concept on the twin concaves is that when you turn the board over on a rail, basically, only half of your board is in the water, correct? If you had one single concave, you'd now have only HALF OF A CONCAVE in the water, which would NOT generate directional thrust, the water could too easily escape? But with twin concaves, ONE WHOLE CONCAVE structure is IN the wave, and the water is being forced/directed/channeled out the tail of the board, creating both increased speed and squirt. Freedom/success in surfing (any kind...) is closely dependent on speed, so anything you can do to make your boards faster is a good thing.

Here's a few photos from yesterday's explorations............if you could get the right one, you'd scream off down along the underwater point. Just super fun. Water, 62, air temp, mid 70's. The rain has cleared and it's back to..................Wintertime in California.
Attachments
Gaviota Coast w_ Walter, Feb, 2015 0009.jpg
Gaviota Coast w_ Walter, Feb, 2015 0001.jpg
Gaviota Coast w_ Walter, Feb, 2015 0011.jpg
Gaviota Coast w_ Walter, Feb, 2015 0015.jpg
Gaviota Coast w_ Walter, Feb, 2015 0018.jpg

Gorillasurfer
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Re: bellyboard for BIG guy

Unread post by Gorillasurfer » Wed Feb 11, 2015 9:36 pm

Nice pics Skiff! I am hoping to get out tomorrow.

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nomastomas
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Re: bellyboard for BIG guy

Unread post by nomastomas » Wed Feb 11, 2015 11:57 pm

I agree with both Skiff and s-glider. What I would call "closed-end" concaves provide lift. The lift is supplied by the diversion of moving water from a line parallel to the bottom, to more more downward flow. For this effect to take place, the entire concave must be in the water, as S-glider states. This "lifting" action is best shown by the "spoon-in-the-faucet-flow" demonstration. Turn on a faucet, hold the concave curved side of the spoon into the water flow and observe the spoon being push away from the flow or "lifted". Conversely, hold the convex side of the spoon into the water flow, and feel the spoon being pulled into the flow. "The typical nose-concave on a nose rider works on this principle, with the lift generated preventing the bottom from sinking too deep and causing drag when the riders weight is on the nose. The bi-lateral concaves in a dual-concave bottom work in a similar fashion as Skiff mentions. These dual concaves are located on each side of the stringer in the rear of the bottom, which is the part of the bottom with most contact with the water during a turn. Lift here (on one side or the other) keeps the bottom from sinking too deep and causing drag when turning.

Concaves have a secondary function which is described by Dick Brewer in "The Surfbook: How design drives performance". Brewer points out how concave bottoms change the shape of the rail, increasing the angle of attack of the rail relative to the wave face, which results in more upward lift captured from the flow of water up the wave face. Brewer adds that V bottoms do just the opposite, releasing more easily from the wave face. When I put V in the tail of my longboards, its because I want the rear third of the board, when weighed, to drift down the face while the front 2/3 of the board is drawn up the face, resulting in a nice, short-radius turn. The combination of dual concave and V (some call spiral-V) results in a particularly loose performing bottom. The impact of concave on rail performance is mostly seen in single-concave boards. Single-concave boards, without a little V to encourage release, are indeed stiff, but extremely fast. The force of the rider's weight brought to bear on the rail is converted into forward motion as the rail bites into the upward flow of the wave.

But there is a second type of concave which I refer to as an "open" concave, which while closed at one end, is completely open at the other. Like half of a funnel. Bonzer concaves are the best examples of these open concaves. These concaves primarily serve to direct water flow. But, when located close to the rail, they can also serve enhance the rail shape. On the G4, I want these open concaves to (1) act more like afterburners, encouraging water accelerate out the back of the bottom, and (2) to enhance the tail rail, giving it more "bite" into the wave face. Just my $.02...
"This is a paipo site...isn't it?"
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Gorillasurfer
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Re: bellyboard for BIG guy

Unread post by Gorillasurfer » Thu Feb 12, 2015 6:13 pm

Finally got out today. Just had enough time to go to my local spot, Bolsa Chica between towers 16 and 17. The board worked great! Especially on steeper, more critical waves. This little thing goes SO FAST! I love the length and there is a perfect amount of float for my taste. Never felt corky but, was able to get on plane fairly easy. I bought a couple sets of fins while I was waiting for the board to be built and tried some T1's today. If you don't know, they are a large twin fin set. I also have a set of the Vector Rasta Keels which I will try another time. I was able to put the board right in the pocket and pull late take offs without sliding out. A very responsive board with great performance. I took the advice of Nomas and used an ankle leash instead of a wrist leash. No problems kicking and forgot it was there most of the time. I appreciated the length when I blasted into the closeout shore break at the end of a few long rides. Thanks so much Nomas. I am totally stoked!!
On a side note, I saw a couple guys in the water having fun on some surf matts. Spoke to one of them and they were 4th gear flyers. Cool stuff.

John Mellor
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Re: bellyboard for BIG guy

Unread post by John Mellor » Thu Oct 08, 2015 1:47 am

nomastomas wrote:I agree with both Skiff and s-glider. What I would call "closed-end" concaves provide lift. The lift is supplied by the diversion of moving water from a line parallel to the bottom, to more more downward flow. For this effect to take place, the entire concave must be in the water, as S-glider states. This "lifting" action is best shown by the "spoon-in-the-faucet-flow" demonstration. Turn on a faucet, hold the concave curved side of the spoon into the water flow and observe the spoon being push away from the flow or "lifted". Conversely, hold the convex side of the spoon into the water flow, and feel the spoon being pulled into the flow. "The typical nose-concave on a nose rider works on this principle, with the lift generated preventing the bottom from sinking too deep and causing drag when the riders weight is on the nose. The bi-lateral concaves in a dual-concave bottom work in a similar fashion as Skiff mentions. These dual concaves are located on each side of the stringer in the rear of the bottom, which is the part of the bottom with most contact with the water during a turn. Lift here (on one side or the other) keeps the bottom from sinking too deep and causing drag when turning.

Concaves have a secondary function which is described by Dick Brewer in "The Surfbook: How design drives performance". Brewer points out how concave bottoms change the shape of the rail, increasing the angle of attack of the rail relative to the wave face, which results in more upward lift captured from the flow of water up the wave face. Brewer adds that V bottoms do just the opposite, releasing more easily from the wave face. When I put V in the tail of my longboards, its because I want the rear third of the board, when weighed, to drift down the face while the front 2/3 of the board is drawn up the face, resulting in a nice, short-radius turn. The combination of dual concave and V (some call spiral-V) results in a particularly loose performing bottom. The impact of concave on rail performance is mostly seen in single-concave boards. Single-concave boards, without a little V to encourage release, are indeed stiff, but extremely fast. The force of the rider's weight brought to bear on the rail is converted into forward motion as the rail bites into the upward flow of the wave.

But there is a second type of concave which I refer to as an "open" concave, which while closed at one end, is completely open at the other. Like half of a funnel. Bonzer concaves are the best examples of these open concaves. These concaves primarily serve to direct water flow. But, when located close to the rail, they can also serve enhance the rail shape. On the G4, I want these open concaves to (1) act more like afterburners, encouraging water accelerate out the back of the bottom, and (2) to enhance the tail rail, giving it more "bite" into the wave face. Just my $.02...
Hi Patrick -

With all due respect, there may be a third type in which a single concave may interface with tail rocker in such a way as to create a FLAT spot in the specific direction of water flow against the bottom. A straight edge held diagonally across a specifically shaped single concave demonstrates clearly what is going on.

I guess the big question is: "Is flat really fast?" I suspect that this a true statement. Many surfboards have been shaped with a flat 'accelerator pedal' strategically placed in the rocker - often just ahead of a rider's stance. I think this single concave/tail rocker interface is often overlooked as a source of speed. Check the 1:00 mark on this video and love or hate the guy, try getting your head around what he's up to... https://www.youtube.com/watch?v=887oTdGshzM

soulglider
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Re: bellyboard for BIG guy

Unread post by soulglider » Thu Oct 08, 2015 8:31 am

is there an english version? mite?
deathbedpaipo.blogspot.com

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nomastomas
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Re: bellyboard for BIG guy

Unread post by nomastomas » Thu Oct 08, 2015 11:03 am

You're right John, concave does that, too! I watched that video almost two years ago, but didn't really get it until just recently. The key for me was coming to the realization that a surfboard moves in a diagonal path to the beach, not parallel to it. And while riding a wave, as Maurice says, water flows across the bottom at about a 45* angle (+/-) to the centerline, not straight down the centerline. What I'm trying to "see" in my mind is what the water flow looks like at the intersection of the rail-and-bottom with the wave. I think it would be something similar to air flow around a a swept-back airplane wing...?
"This is a paipo site...isn't it?"
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John Mellor
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Re: bellyboard for BIG guy

Unread post by John Mellor » Thu Oct 08, 2015 5:09 pm

Hi - Yes, that rail foil thing has always intrigued me and plays a big part I'm sure. Photos and videos are good ways to assess how much of the rail is actually penetrating the water surface. As with any penetrating foil, there must be an optimal leading edge, thickness placement, and exit taper. An airplane wing is about as functional a foil as any to try to replicate. Surfboard fins, boat keels, aircraft wings all seem to fall in to a basic configuration. The devil is in the details and how it all fit together!

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