A certain highly-respected someone recently stated that concaves “have always been used to provide control”.
This goes against the vastly popular notion that concaves add lift and therefore leads to more speed.
At first I was taken back by this and was thoroughly confused by it. But upon a day’s thought, there seems to be something to it. Something very real. But my thoughts only jive with multi-fin systems, particularly thrusters (btw, I really like the term ‘thruster’). I remember Greg L saying that he really liked concaves on single fins back in the day, which sort of goes against my thoughts.
Concaves (except the “dimples” ones) are all more or less directional and thus provide drive which in turn provides control. That’s my take, but I may be wrong.
Concaves IMO give instant speed and control but tend to track and that is where the shapercomes into play and adjusts other board dimensions to make it work.After surfin the flat bottom sunova and then gettin back on my coil which has deep concave I can say the the coil went faster and got up on plane faster as well.
Yikes… woooo… I tried to reply and my server said I couldn’t perform that action…
Anyway - I think it depends on where the concave is, how big (deep, wide, etc.) it is, etc…
There always seems to be someone saying the full board concave is to make the rocker straighter/flatter so the board should be faster from that, w/curve on the rocker… I can see that, as we mostly ride on one side or the other.
I’d argue by definition, concave=high pressure=lift, but with the provision - the concave needs to be within a “flat” surface.
As for control… I don’t know. I guess if you have the deep ones in/out the tail it may add some direction to the water flow… Like the six channel thing, but then again, I’d argue that bottom does not add up to a concave surface.
You told me this before and I’ve looked at a lot of concave boards and I have a reasonable understanding, but I might as well ask you to refresh me here since the exact issue is on the floor right now.
Where and how much and where should it begin and end? Asked without too much specificity
but
say, for a 6’4" board with 3.5 nose rocker, 2 of tail, and about 21 wide, 15 nose 16 tail, diamond tail with facets about 1-1.5" deep, about 9" point to point, a curvy outline with width for mushy surf.
I’m going to disagree with you all! But I realize that I could be totally wrong, since my shaping experience is way below just about everybody here on Swaylock’s.
I’ve found that concave improves speed and the ability to “flick” the board into a turn. It makes the board feel lighter, like a rock skipping across a pond. Get a little wind chop or backwash coming up the face and the board can suddenly become a victim of the elements.
Vee is for control. It makes the board more steady.
janklow, with those dims and rocker, I’m not sure I’d advise any concave at all. It’s all got to go together. Flat rocker and width kinda negates the need. In general (and I hate to over-simplify, but this is a complex subject), the big single concave works on boards with more rocker, narrower width, and less volume.
You could do a slight single through the center. Or flat to a slight V with a double concave through the V between your feet. But dead flat all the way is hard to beat for that type of board.
the way its been explained to me…
is that anything beyond perfectly flat increasies the surface area the water must interact with.
So as the water touches or pushes against the bottom surface it slows down and doesn’t accelerate some folks think.
Turbulence and back pressure has something to do with it as well.I don’t think you get lift like you do with a wing because the fluid isn’t traveling both over and under the foil surface like a wing. Maybe the lift effect is more applicable to fins which are mostly submerged in the fluid.
so the faster the release and cleaner the release you have of getting the water off the bottom of the board the faster you should go and the more contact or drag you have with the water the more control you should have. That’s why singles and doubles or combinations of them have more control than say a deep 6 channel bottom which can get pretty turbulent when the water is “fluffy” llike in white water. Deep concaves were basically a way to flatten the cottom rocker in the old banana rocker boards they were put in back in the 80’s.
I think this is also one of the reasons that the tow in guys tend to hop over the bumps in the face so that they can free the bottom of their board from touching the water surface to keep their speed up. Kind of similar to the foils they use.
its all beyond my understanding but that’s kind of how chandler and others have talked about it.
I always thought my Gemini was faster than any board I rode but I was probably just riding on a bubble of air stuck under there. Banana peel surfing is hard to master as well.
A lot of people think lift is only from foils – but planing is lift – the very thing that is surfing. Redirection of flow is lift – concave enhances it. It enhances control surfaces’ control, vastly enlarges high-performance surfboards’ abilities under skilled, energetic feet, and yes, it engenders some drag – all that is due to lift. There are trade-offs inherent in any design choice. Sorry if this sounds strident, but this is all revolving around a fundamental thing.
Flat is only when you can put a ruler against it. So even when a board is flat across [perpendicular to stringer] a surfboard, it might still be Vee-d when that same line is angled 45 degress on stringer [from halfway of the left rail, to the right rail behind the side fin]
…and the more contact or drag you have with the water the more control you should have.
hmm, interesting. Everysurfer mentioned the word ‘flick’…Ive felt that too with with concaved boards. I made two boards that were difficult to surf cuz they were squirrely both had deep concaves. Otoh, boards with concave drag (speed control) going straight. I dunno man, maybe the certain someone needs to speak.
Here’s the funny thing…here are some choice words used to sell concaves: lift, squirt, channel, speed, thrust, drive (doh!), Im sure there are others. Control is not a word commoly used to (sell) describe the affects of concave. I dont think I ever heard it until recently.
Here’s the thing I really noticed. Three or multi finned single concave boards drag big when going straight, the more concave the more drag. Flat bottom with same fin setup dont. I really feel that going straight, typically used to get around longer white sections in the flats, is vital to linking sections of the wave. It also feels very liberating being able to go straight without that drag. Now I think three fins do everything else really well, except going straight with concave. So for my personal needs, why would I hinder myself with concave - I can get the best of everything without it.
Mike you answered J’s questions just as I would. Concave is totally unecessary with flatter boards. I have a board almost exactly as J described, except its tail is 15 similar to a rusty pirahna. Tried all kinds of fin setups on that one and stopped after using five fins. Man I love fins.
I remember a Jbay contest a few years back when Andy Irons was doing well, half way thru his ride he came off the top kind of late and tried to project straight on the flat ahead of a tubing section, his board hit the break so badly he almost went over the nose - just from the drag. Now if I were a world class designer, I’d do everything in my power to get rid of that. Especially if he lost a heat because of it. Why would anyone want that to happen?
Oh btw, too much tail rocker has a similar breaking drag affect as too much concave. And yes, I realize rockered boards with concave are meant to be on face or on rail. Thats why I said for my own personal needs.
I’m glad you explored all that, D – I’m leaning toward a slight single through the middle – I feel like I may have to go with a bit more width if I go completely flat, for wavecatching. If I had my choice I might do one of each with the same shape otherwise!
Slight single concave is what i have on the board I mentioned. But going from slight concave, to flat to slight vee would have significant affects. I know surfercross’ griffin has a slight vee running and mine is dead flat. GG bottoms are so flawless and pristine. Oneula knows. Oneula likes to play humble but the dude knows his shit. Gotta love’m for that. It pays to pay attention. Glad I did. Graphic by Barnfield, reposted by osmosis.
Instant speed is the name of the game for most high performance surfing.
Re the comments on concaves increasing wetted area and therefore drag; you’d have to do a ridiculously deep concave to increase wetted surface by even one percent. That argument doesn’t hold water. (or you can just read Karl’s comment above).
Then there’s a whole other aspect of concave function that would come under the ‘‘control’’ heading. I haven’t seen it discussed here.
That said, I’ve done dead flat bottoms a lot, for over 20 years. They work great on boards that have a lot of planing surface and volume. Some of my personals are dead flat.
