Has anyone out there experimented with angular concaves (what can also be described as an inverted vee)?
What I am describing is a “concave” without curves.
I am positive that some of you have experimented with this in the past, so I would like to know your thoughts before I give it a try. I have some theoretical ideas on how it would function, but I would like to hear thoughts from those who have actually done the testing.
Hmmm…. Interesting.... So, what would happen if you made a turn? Wouldn’t the water flow across the bottom diagonally (I.e., not parallel to the stringer)? If my understanding is correct then the corner of the V would interrupt the water flow, and create turbulence. I can’t say if this would be a good thing or a bad thing. My guess would be the former
Like this?
http://www.surfysurfy.net/2010/11/channel-bottoms-are-groovy.html
Some say it works, others say it doesn’t and apparently someone thinks beacons is a fast down the line wave.
My bet is you couldn’t tell the difference between flat panel concave and curved concave. As long as the stringer and rail rocker keep curving. If you make a flat spot along the stringer or rails, you get a sticking point.
Where the concave starts, ends, depth and width matter. I’m guessing it’s about how much water gets directed under there, not the shape.
But I’d prefer I was proven wrong, and learned something new.
Consider that the water in a wave is moving up toward the sky, hits hull bottom and is deflected across the bottom diagonally during most surfing turns; and the main function of concave, whether flat or curved, is to direct water flow aft (i.e parallel to the stringer).
So I don’t think the corner would cause much turbulence.
I like the term you used, “flat panel concave”.
I do think, though, that the shape will make a difference (maybe not though, thus the thread ;-) … consider the opposite extreme of the flat panel concave, a concave with an extreme curve, or “hook” at the rail. I made a board with too much hook in the concave, and it lacked control because it tracked and didn’t initiate turns quickly. I attribute that to the build up of pressure on the rail (because of the greater change in water flow direction at the hook), which took extra effort to overcome and initiate the turn. With a flat panel, the distribution of pressure would be even, and theoretically more control. Also, the center line angle (and consistent panel angle for that matter) could provide a more consistent feedback in turns, similar to the effect of a hard tucked rail from nose to tail, i.e. Greg Griffin.
I don’t think that it is just a matter of how much water is directed, but also the distribution of pressure created by the change in flow direction.
Probably not ‘exactly’ what you’re talking about , but Dick Van Straalen’s been doing it for years.
Or it could be like a light switch, all on or all off. The transition from catching water to not could be abrupt… a sticking point. Gradual curves are more like a dimmer switch, a gradual increasing or decreasing effect. Smoother.
If that were true wouldn’t a flat bottom have sticking points? In my experience a flat bottom provides better release and control, but lacks in the drive provided by a concave. IMHO the main function of a concave is to “load” the AoA of the hull, just as putting the board on its rail increases the AoA, and increases lift. So, theoretically, you can maintain the release and control of the flat bottom with the benefits of increased drive from the increased AoA of the hull.
Of course this is all conjecture.
Is it inverted vee ?
A friend of me start to use it, all riders say boards feel good. I use it now and boards seems to work well. No tracky feeling that i experiment with my old over curve concave. Easiest to shape well for me.
Sorry for my frenglish.
Although they make sailboards,these guys have been using inverted vee for a few years and claim it works. However, their shapes are quite different from the norm, so it’s possible that it only works in conjuction with other specific design elements.
A flat bottom wouldn’t have a sticking point, because there is one continuous surface. No transition from the “On” to the “Off” position. You only feel an uneasy transition if the change in planing surfaces is abrupt.
A rockerless design wouldn’t have a “sticking point” because the whole board would track the same no matter where you stood or what you did.
The sticking point I’m thinking about is the abrupt transition half way through a turn. Imagine a bottom turn. You are laying it over on the rail and pushing just so hard to get it to change direction. As you go through the turn your effort changes, and you begin to push harder off the bottom.
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Right at the lowest part of the turn, right in the trough as you start to drive up the face, your legs are compressed and you are straining against the wave as hard as you can. If the board has a sticking point, when you push just hard enough to overcome the flaw in the design, “woops” you just slid out, because you just transitioned onto the other planing surface and lost control.
The smoother the design the easier it is to feel the response the board is giving. You know that if you push just a little harder, the board will react just a little more. A direct proportion of effort “in” to direction of change “out”.
I used to do all my boards like this as DVS was a huge inspiration on my early boards, and I thought it would be easier to do than a curved surface - which is actually not true!
To be honest, I can’t tell the difference between the inverted vee vs the concave. There is no abrupt on/off position because just like a normal concave it slowly blends in and out again. There is no “break” in the bottom curve if it is done right.
The water enters the “concave” and follows the stringer just like it would in a curved surface. The bottom curve changes just like a normal concave, so I can’t see where you would actually be creating a flat spot by doing it this way.
Best thing to do is just make one, and see…
George has been using that as his main selling design element on all his longboard for at least a decade or more.
Claims that its more efficient and responsive than a concave bottom.
You can read about him below
http://custom.surfboardshack.com/george-ku-hawaiian-surf-designs/
The board would only be flat parallel to the stringer (although at an angle), at any other angle it would be curved because of the rocker curve.
Do you have any photos of boards with this bottom configuration?
Awsome… this is what I am looking for, I have never heard of George, I just wish there were more pictures and descriptions of the design element.
Have you ridden one?
I would expect it to be more responsive than a curved concave.
This is exactly what I would expect from a flat panel concave or inverted vee (I know you are saying the opposite)… a corollary of this in surfboard design is the flat, toed fin. Flat fins with toe seem to be more responsive than curved fins, and/or fins without toe.
I think that this is the case because the consistent AoA of the flat surface provides consistent and clear feedback to the rider, so when you put the board on it’s rail, rather than changing the pressure distribution gradient (with a curved concave), the rider is only manipulating the AoA, and not the pressure distribution.
I also find the consistency of the complete, hard, tucked rail edge (i.e. Greg Griffin) to provide a similar consistency of response throughout all parts of a turn and different types of a turn. With a curved concave (especially ones that are not designed correctly/efficiently), there is a lack of consistency of responsiveness at different AoA’s.
well, that depends on how you do it. Surely a normal concave follows the same curve parallel to the stringer. Although if done to flatten the stringer rocker, it will transition to the rail rocker just like an inverted vee.
I’ve done a few boards with a certain modern guru, and he puts his single concave in such a way that they are actually flat if you put the straight edge on them diagonally, moving almost to center . But, they follow a certain rocker from nose to tail. Inverted vee is only flat from rail to rail, it isn;t necessarily flat nose to tail, or diagonally… just saying
Ya, obviously I misspoke. I meant that it would be flat Perpendicular to the stringer.
I am familiar with the concept of adding concave so that the intersection of rocker curve and concave curve creates a flat spot at a certain angle relative to the stringer… I don’t know if it is the same “modern guru”, but I had a shaper explain to me that he adds the concave so that there is a flat plane at an angle around 13 degrees (or was it 17)? As this is the average (or median or most common??) angle of water flow across the hull bottom.