*** Official Griffin Surfboards Thread ***

One-Off

Tom Curren status
Jul 28, 2005
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I revisited this thread because the hydrodynamic discussion was interesting and informative. I miss the mad scientist's pronunciations. It was so sad to see his posts of the motor bikes.:( But at least, like the saying goes...doing what he loved.

I wonder what GG said to Pyzel about the latter's single with inset double concaves???

Also, an exchange between Mr. J and Senor Sopa about water wrapping around the rail caught my attention this time around. It is a common conception that water wrapping around the rail creates hold. If that is so, why do all makers (and I mean ALL) have hard edges in the tail, where I assume you want the most control? I think Mr J said something about the hard edge on a skimboard creating grip. So what are GG's hard edges forward doing? Releasing=creating speed? Or are they a control element, creating grip? A ridge creating directional stability? Mr J said slight concave with hard edges were slippery. I feel the concave accentuates the release, creating speed at low speed (first turn, immediate acceleration) and then, at high speed, the fins take over for control, reducing the control liability of the hard edges up front. Also the fins reduce the need for a control element in the tail.

Maybe?:unsure:

ps hard edges (chines) have been adopted by the sailing community. Originally it was to induce planing (release) of skiffs and wide hulled race boats. Now it is also seen as adding directional stability in wide hulled cruising boats.


This part caught my attention- “You want to prevent the boat from sucking itself to the water surface. So, adding a flat and wide stern was combined with the hard chine – this combination of design features made the boats entering plane-mode quickly, especially on reaching points of sail and at the same time prevented the fast hull to suck itself to the surface hence slowing down.”

Release!



"The line of the chine at the same time adds directional stability making the yacht want to sail in a straight line."

(Directional) Stability!
 
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feralseppo

Billy Hamilton status
Feb 28, 2006
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I revisited this thread because the hydrodynamic discussion was interesting and informative. I miss the mad scientist's pronunciations. It was so sad to see his posts of the motor bikes.:( But at least, like the saying goes...doing what he loved.

I wonder what GG said to Pyzel about the latter's single with inset double concaves???

Also, an exchange between Mr. J and Senor Sopa about water wrapping around the rail caught my attention this time around. It is a common conception that water wrapping around the rail creates hold. If that is so, why do all makers (and I mean ALL) have hard edges in the tail, where I assume you want the most control? I think Mr J said something about the hard edge on a skimboard creating grip. So what are GG's hard edges forward doing? Releasing=creating speed? Or are they a control element, creating grip? A ridge creating directional stability? Mr J said slight concave with hard edges were slippery. I feel the concave accentuates the release, creating speed at low speed (first turn, immediate acceleration) and then, at high speed, the fins take over for control, reducing the control liability of the hard edges up front. Also the fins reduce the need for a control element in the tail.

Maybe?:unsure:

ps hard edges (chines) have been adopted by the sailing community. Originally it was to induce planing (release) of skiffs and wide hulled race boats. Now it is also seen as adding directional stability in wide hulled cruising boats.


This part caught my attention- “You want to prevent the boat from sucking itself to the water surface. So, adding a flat and wide stern was combined with the hard chine – this combination of design features made the boats entering plane-mode quickly, especially on reaching points of sail and at the same time prevented the fast hull to suck itself to the surface hence slowing down.”

Release!



"The line of the chine at the same time adds directional stability making the yacht want to sail in a straight line."

(Directional) Stability!
I think I read or saw somewhere that McTavish said when they started putting the hard edge in the tail it was to keep the board sliding out? Might have been a discussion in that Mick Fanning single fin video where he made a board for him that he rides a Lennox.

GG's boards kind of feel like putting a snowboard on its edge (gouging into the face of the wave) and the rail releases with little effort never feeling sticky or catching.
 

santacruzin

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GG's boards kind of feel like putting a snowboard on its edge (gouging into the face of the wave) and the rail releases with little effort never feeling sticky or catching.
good explanation! if you are used to deep concaves it will take some getting used to as well. If you use your backfoot and have the correct foot placement it is magical!
 

One-Off

Tom Curren status
Jul 28, 2005
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It’s been one of the things I’ve pieced together reading Griffin’s posts over the years. Greg views concaves as a control element on boards. To add liveliness/responsiveness move fins forward.

Most shapers say concave adds lift. I’ve always repeated that until I rode a Tokoro X3. Wade did a model with a flat bottom. The board was fast but not from the usual rider input. On my boards with concave I can feel the bottom grip the wave and I’d push off that to get speed. The flat bottom didn’t have that gripping feeling and at first I didn’t think I was going fast cause of the lesser return in rider input. But the board was flying.

When I posted about my experience Griffin replied that concaves are a control surface or something cryptically similar.

I could be totally wrong and am happy to be corrected.
You were going fast without rider input. Did you feel out of control?
 

One-Off

Tom Curren status
Jul 28, 2005
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I think I read or saw somewhere that McTavish said when they started putting the hard edge in the tail it was to keep the board sliding out? Might have been a discussion in that Mick Fanning single fin video where he made a board for him that he rides a Lennox.

GG's boards kind of feel like putting a snowboard on its edge (gouging into the face of the wave) and the rail releases with little effort never feeling sticky or catching.
So for you the hard edge up front is a control/grip element? That sounds right. But it also sounds like a little concave would increase that, like getting a head start on putting the board on edge.
 

20W-50 and blood

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I think I read or saw somewhere that McTavish said when they started putting the hard edge in the tail it was to keep the board sliding out? Might have been a discussion in that Mick Fanning single fin video where he made a board for him that he rides a Lennox.

GG's boards kind of feel like putting a snowboard on its edge (gouging into the face of the wave) and the rail releases with little effort never feeling sticky or catching.
random side note...wy do i see your avatar phto pic thing and feel liek im getting awesomely stabbed?
 

ghostshaper

Phil Edwards status
Jan 22, 2005
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This is how I've always learned how water reacts:
hard edge = release = fast
curve = wrap, control = slow

roundpins hold; square tails release

Hard edges don't "grip" the water. I remember reading why hard edges on skis/snowboards exist: something to do with the pressure melting water on the snow when on edge, which creates more lube for glide/speed. Snow is totally different than a liquid water medium, though.

Edit: try sanding your hard edge tail and surf it. Or, add a hard edge w/ tape acting as a resin dam.
 
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One-Off

Tom Curren status
Jul 28, 2005
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This is how I've always learned how water reacts:
hard edge = release = fast
curve = wrap, control = slow

roundpins hold; square tails release

Hard edges don't "grip" the water. I remember reading why hard edges on skis/snowboards exist: something to do with the pressure melting water on the snow when on edge, which creates more lube for glide/speed. Snow is totally different than a liquid water medium, though.

Edit: try sanding your hard edge tail and surf it. Or, add a hard edge w/ tape acting as a resin dam.
Waterski hard edges seem to grip.
 
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PRCD

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Also, an exchange between Mr. J and Senor Sopa about water wrapping around the rail caught my attention this time around. It is a common conception that water wrapping around the rail creates hold. If that is so, why do all makers (and I mean ALL) have hard edges in the tail, where I assume you want the most control?
The turn is initiated off your front foot where you want hold, but then shifts to the back as you lift your torso off the bottom turn. At this point, you're on your tail and want release.

I think Mr J said something about the hard edge on a skimboard creating grip. So what are GG's hard edges forward doing? Releasing=creating speed? Or are they a control element, creating grip?
Here's what I think and feel free to poke holes in it. GG's forward rails under your front foot are round where the board is heeled-over in a bottom turn. They hold just fine when you're leaning. When you're more upright, they're sharper for releasing when you twist. They become sharper and less round towards the tail, just like a normal thruster. However, the ModFish 2 is really a small wave board for somewhere like FL or N. San Diego County.

I think this is also what's happening with a skimboard. The turns they make are mostly twists rather than leaning turns, so the edges create a ton of release. Kind of a different application though b/c they're mostly concerned with planing.
 

One-Off

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The turn is initiated off your front foot where you want hold, but then shifts to the back as you lift your torso off the bottom turn. At this point, you're on your tail and want release.
Bottom turn yes. Cutback, you're unweighitng and then putting all your weight on the heel of your back foot. Those edges back there need to hold.


Here's what I think and feel free to poke holes in it. GG's forward rails under your front foot are round where the board is heeled-over in a bottom turn. They hold just fine when you're leaning. When you're more upright, they're sharper for releasing when you twist. They become sharper and less round towards the tail, just like a normal thruster. However, the ModFish 2 is really a small wave board for somewhere like FL or N. San Diego County.

I think this is also what's happening with a skimboard. The turns they make are mostly twists rather than leaning turns, so the edges create a ton of release. Kind of a different application though b/c they're mostly concerned with planing.
I like the idea that they are two different things depending on their angle of attack. I take your term "twist" to mean turning flat. When turning flat (and I'd say when going slower) they're releasing. When going fast and put on edge (a hard turn) they're acting like the chine on the sailboats, creating directional stability.

My sensation riding boards with full length hard edges, the one that keeps me adding the to the boards I make, is that on take off, when you're not up to speed yet, you do a small check turn and everything releases, and that gets you immediately get up to speed. That's what I like, the quick acceleration. On the flip side, I've never had any sensation of not being able to sink a rail and do a hard turn . The release did not hinder the hold.

Than you GG for the inspiration.

Now if we could make a bottom that turns flat when you hit a flat spot on the wave, and then sucks in concave when the wave hollows out, then we'd be onto something. When I worked at the sailboat shop, the foreman, who had been the manager of the North Sails loft in Seal Beach, would talk to me about his idea of adding panels to the sides of keels with small hydraulic pistons that would change the shape of the keel's foils to create lift on the side needed. I thought it was kind of genius.

pps For years I would misunderstand what Greg was saying because, coming from the sailing background, lift always translated to low pressure (with the hull appendages that I was shaping, and with sails).
 
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jkb

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Now if we could make a bottom that turns flat when you hit a flat spot on the wave, and then sucks in concave when the wave hollows out, then we'd be onto something. When I worked at the sailboat shop, the foreman, who had been the manager of the North Sails loft in Seal Beach, would talk to me about his idea of adding panels to the sides of keels with small hydraulic pistons that would change the shape of the keel's foils to create lift on the side needed. I thought it was kind of genius.
Would an inverted vee accomplish this? Like the image on the bottom running through the board. Put it on rail and it acts like a flat bottom. Going straight it acts like concave.

1662600502919.png
 

need 4 speed

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Would an inverted vee accomplish this
The board I rode a 3 mile (with you) was inverted vee. From my experimenting with it, best to keep it subtle
The last two I made were flat to subtle vee in the tail (with concave). I think I like better, putting it in with shape3d messes with the rail rocker and I don't want to carve in by hand, so I left it behind
 
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Senor Sopa

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Mar 11, 2015
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I think you want the opposite, when on rail you want that control. When going straight you want the release/speed.
The pull from water wrapping is real. I strongly urge you to do the spoon test, both sides!
I believe the edge provides an "entry" point for the flow to bifurcate.

Let's bring the term, harmonics, into the conversation.
Pretty much all objects have specific patterns they tend to vibrate in. Flow is similar. At slow speeds, like early take-off, the flow pattern may not be optimal. This is what the "shake rattle and roll" that One-off referred to. That first teeny wiggle sure seems to get the boar going. Huh, what? The motion changed the flow pattern towards the one we want for max shreddage. Perhaps the hard edge up front also enhances this transition.

Take a look at underwater photos, notice how much of the rail is engaged. I believe most of the hold is from the front part of the rail. The thin tail is mostly a control feature, also providing a clean exit for the flow.

The rail line almost parallel to the stringer is the real foil that is in effect. It's pretty long and not very wide, with a nice soft leading edge. The pressure diff between the rail touching the wave and the bottom of the boar is our equation to be solved.

Is it too early to introduce the continuity theory?
I will make the observation that the transition between the velocity of the boar and that of the raw wave occurs over a short distance. Whenever there's a high velocity gradient, interesting things happen.
 

ghostshaper

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I'm going to throw in another variable to think about:
opposite rail line (when water is shedding across the board on the opposite rail) in a turn
 
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Mr J

Michael Peterson status
Aug 18, 2003
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...
Also, an exchange between Mr. J and Senor Sopa about water wrapping around the rail caught my attention this time around. It is a common conception that water wrapping around the rail creates hold. If that is so, why do all makers (and I mean ALL) have hard edges in the tail, where I assume you want the most control? I think Mr J said something about the hard edge on a skimboard creating grip....
This is where Senor Sopa and myself disagree. Link to my belief here *** Official Griffin Surfboards Thread *** | SURFER Magazine Forum | Surf News, Fantasy Surfer, Photos, Video, and Forecasting and here *** Official Griffin Surfboards Thread *** | SURFER Magazine Forum | Surf News, Fantasy Surfer, Photos, Video, and Forecasting
TLDR: I don't disagree that there is water wrapping the rail (although not as much as some people think). I don't disagree that the laws of physics say wrapping the water inwards to the deck is going to create an opposite force pulling the rail into the wave. What I say this force is completely cancelled on a soft round/full rail. The planing effect pushes such a rail out of the wave and the board holds less.

The hold of a rail therefore does not come from the rounded part of the rail, it comes from the flat bottom, for this to happen the board must be biting into the wave and banked over if in the flat trough. We can think of the flat bottom as highly canted fin - not the most favourable angle of attack for sideways hold, but providing some nevertheless, bonzer runners are highly canted, but I am sure provide some hold. Conceptual diagram below.


flat bottom hold.png
 
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Mr J

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... I think Mr J said something about the hard edge on a skimboard creating grip....
So I think a skimboard rail grips well (only when banked in deep water) for two reasons.
1. Because I believe it is the flat bottom that creates the hold, then the hard edge extends that holding surface right up to the perimeter of the rail. i.e maximises the available holding surface.
2. The skimboard rail is thin/pinched - this allows greater penetration of the rail which results in a greater area of banked hull holding area submerged - so more hold. Just like a fin with larger area gives more hold.

The same principle applies to surfboars - pinched rails grip more, taking the edge close to the perimeter grips more. Except we have to balance out maximising hold with producing something that is sufficiently forgiving that we can control it, so we need the planing effect of a rail with more volume and more rounded than a skimboar. The skimboar riders don't pump their boards like we do - they can only do the fish killer/huntington hop pump. The beachside rail of skimboar would catch horribly otherwise.
 
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One-Off

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This is where Senor Sopa and myself disagree. Link to my belief here *** Official Griffin Surfboards Thread *** | SURFER Magazine Forum | Surf News, Fantasy Surfer, Photos, Video, and Forecasting and here *** Official Griffin Surfboards Thread *** | SURFER Magazine Forum | Surf News, Fantasy Surfer, Photos, Video, and Forecasting
TLDR: I don't disagree that there is water wrapping the rail (although not as much as some people think). I don't disagree that the laws of physics say wrapping the water inwards to the deck is going to create an opposite force pulling the rail into the wave. What I say this force is completely cancelled on a soft round/full rail. The planing effect pushes such a rail out of the wave and the board holds less.

The hold of a rail therefore does not come from the rounded part of the rail, it comes from the flat bottom, for this to happen the board must be biting into the wave and banked over if in the flat trough. We can think of the flat bottom as highly canted fin - not the most favourable angle of attack for sideways hold, but providing some nevertheless, bonzer runners are highly canted, but I am sure provide some hold. Conceptual diagram below.


View attachment 137663
Ok. Couple of thoughts. The spoon experiment. The water wrapping a curve. I don't like that to illustrate water going over the rail. The water going over the rail is notmoving anywhere close to perpendicular, up the rail. It is wrapping the rail at an extremely oblique angle. In fact you said you've looked down to observe barely any water wraps onto the deck. The outline is the curve the water is wrapping. Makes me wish GG was here to explain his area reduction by curve in tail...

I agree with your assessment about the skimboard. I went to look at that Domke guy riding waves and it is not the edge holding, it is the whole board. So like you said, it is the flat bottom. And, like you've said previously, a concave increases the angle of hold.

I'm curious to why you felt slight single made the board slippery (did not help hold)?
 
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Mr J

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@One-Off I did a very brief experiment when I had finished washing my wetty today. Brief because I was getting cold. I dragged a plastic spoon across the surface of the water in my washing bucket. I was holding it by the end of the handle and dragging lengthwise applying a little downward pressure. It did not dive to the bottom - it planed across the surface. There is a difference between a thin stream of water from a tap and the mass of water behind a 12 second period wave. That's why I don't believe hosepipe experiments have much value either.

Its just experience that tells me wide light single in powerful waves gives a feeling of sitting out of control on the surface - I reverse engineered the theory that the it is the lift of the concave from water exiting the rails diagonally. Wide for me starts at 19", because of this experience I only ride narrow and this stops the out of control feeling in powerful waves. You have made light single concaves - how wide and how long were they and did you get to take them out in reasonably powerful waves? What was your impression?