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Re: Do concaves work? [Re: DublAK2] #2906490
01/31/19 07:00 AM
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
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
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.


Legal Disclaimer: jkb's posts are written by his Posting Agent, whose views and opinions do not necessarily represent those of jkb.
Re: Do concaves work? [Re: DublAK2] #2906994
01/31/19 11:02 PM
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.


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Re: Do concaves work? [Re: DublAK2] #2907013
01/31/19 11:49 PM
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
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
02/01/19 09:59 PM
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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
02/01/19 10:25 PM
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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
02/02/19 03:44 PM
02/02/19 03:44 PM
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The simplest machine is the best machine.

Re: Do concaves work? [Re: DublAK2] #2907675
02/02/19 07:53 PM
02/02/19 07:53 PM
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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
02/02/19 11:57 PM
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Originally Posted By: oakfoils


calling grandpa griff to the suction cup.


Nobody likes suction


Nobody surfs here anymore..........it's too crowded

shaka
Re: Do concaves work? [Re: DublAK2] #2907760
02/03/19 12:45 AM
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

NOT THAT KIND
Re: Do concaves work? [Re: need 4 speed] #2907767
02/03/19 01:10 AM
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
02/03/19 02:18 AM
02/03/19 02:18 AM
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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
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

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