# Flat vs double concave

Question for the physicists and hydronauts

From what I’ve seen the single to double concave seems to be the most widely used bottom in shortboards and even most Grovelers .

it is my understanding that the single up front creates instant lift/speed while the double maintains that lift while adding an element of control to turn once surfing with some velocity, eliminating the “stickiness” of a single.

however I was thinking, can’t all the functionality of the double concave be achieved with a flat bottom after a single concave? You eliminate the inherent  “stickiness” from concaves that you compensate for when shaping in a double. Also, you’d maintain some speed from a front single concave through the elimination of drag created by the middle spine/vee in a double concave.

could somebody smarter than I please school me as to why the the single to double is so conventional?

Became so popular because it’s what people like or… What people think it’s what they need…

Most surf World explain of concaves works are wrong according physics theory (because usage hypothetis forget…)

Facts is more i use thicker and flatter (less rockered) boards more i like flatter bottoms.

There are lots of misconceptions and plenty of room for debate and arguments.

Here are a few things I think I know about it.  Bottom contours don’t “generate” speed.  A single concave can capture some of the up flow on the face of the wave and translate into forward motion AKA speed. With a really wide tail, like a fish, a little vee helps go from rail to rail easier.  Everything else is a mystery to me.

And, Friction is not your friend, except for a little from fins in the tail.

And I am really doubtful of the benefit to the average bloke of double concave in the tail.  A single concave flowing to flat in the tail ought to be all that is needed.  Heresy, I know. See you in court. Ha.

all the best,

Well that’s what I’ve been thinking too Greg. You put in the double concave to neutralize the negatives of a single to arrive at a net gain of 0.

why not keep it simpler and do nothing to the bottom In the back half to still arrive at a net gain of 0???

BINGO !       Rare insight, in this era of imaginary benefit, from ‘‘loaded dome, double spiral, concave single to double  Vee, flat concave belly.’’      All the foregoing in the last 18 inches of the bottom, at the same time.     What I refer to as a ‘‘Busy Bottom.’’      The foolish extreme, of the concept, that if ‘‘some is good, more is better.’’     You will be well served, by keeping it simple.

Some of my best boards are flat bottoms nose to tail. I agree with Lemat, I’m riding low rockered, wider and thicker short boards with flat bottoms and I really like them. Just make sure the rails are thin.

Well I gues Dick Brewer is an idiot.

I’m a noob shaper, and don’t consider myself to be at all expert, but I want to follow up on this (with greetings to Greg Tate \m/): "With a really wide tail, like a fish, a little vee helps go from rail to rail easier. "

I’m a heavy human (215 lbs+ most days), and am still surfing boards as short as 5-8 at 50+ years old, in Santa
Cruz, in crowds (though I do my best to avoid them, you can’t avoid them…they will follow you every where you go, no matter what you do to avoid them).

IMO, you will get differing opinions on the value of a double or spiral vee in particular depending on the weight of the commenter. As you get into boards that are very stubbed (wide, thick, shorter than your classic “glass slipper” dims to shrink length while enhancing paddle and wave-catching range), you will find longer doubles and more deliberate vees than in classic HPSB boards for lighter riders – not suggesting at all that a good single concave like Stretch is somewhat widely lauded for mastering will not serve the heavier surfer, only that when that same shape is stubbed, you’re more likely to see a long double, or at least a double on it. For me, this has sort of played out (I’m 5-6) to come into play around the 21+" width mark. If you look at many of the hybrid designs from Firewire (e.g. “potato” named shapes), you’ll see that most of them have a long double, and if not vee then an accelerated double under the rider’s feet).

Personally, I want looseness and speed and wave catching in shorter hybrid boards (most of mine, for myself, are 22+ wide and over 3" thick, usually 3 1/8" or 3 1/4" thick. The boards I make for myself paddle better, and catch waves better, than boards of similar volume off the shelf, and perform about the same otherwise. Often I’m copying shapes I’m interested in, to see what’s up with them, but refoiling and stubbing them even more than the original designs are stubbed. Sometimes I’m reducing rocker because in SC the waves are often good but not that juicy.

I also know some other heavier (fatter, or just more lean weight) surfers and they tend to like the same shapes and designs I do, especially if they’re top heavy, i.e. “super hero” silhouette from behind (and maybe sometimes eggplant in profile lol).

BUT, lately I’m also making some wide boards with straight rail lines that have a Tomo styled tail and bottom (quad channels inside a rolled nose to single concave to long double with double barrel transitioning to vee and lesser vee, or even flat, out the tail. On these boards, I don’t have to move my feet to cutback or make a very deep bottom turn. The same boards, without that bottom, I’d have to move my feet to make hard cutbacks or very vertical bottom turns (more a factor on cutbacks or top turns than bottom turns). Again, because of my weight, we’re talking about boards over 22 wide.

IMO, this is related to Greg’s comment on fish shapes. Flatness of rocker, straighter rail lines, and fin layouts must be in play, too, but at least for me it’s the length: width ratio that makes the vee/double more likely to come into play, and then also volume distribution/foil and planshape.

A lot of dubious rambling…

My main point, which I wish I could survey and crunch numbers on: IMO if you survey guys under 185 or 190 lbs, versus over 195, you’ll find a clear break among long time & skilled surfers as far as whether they think vee or spiral vee or whatever variations of vee are important for them to have in daily drivers.

The court of Swaylocks has spoken, off with his head.  Lol

Bat, you make good points. As for me, I’m mostly parroting what Greg Loehr taught me (fish need vee, he shaped 40,000 plus boards) And what works for me in east coast gutless waves without the speed of the pacific.

I will also point to Greg Griffin in his preference for flat bottoms.

Carry on.

All the best

…Hi Greg; not to disrespect but (also I told him at some point here) never ever he really 100% completely handshaped all those boards.

Anyway; a fish is way better to not have a V and not have a thruster set up; only some rocket fish would. Longest fish at 6 or 6 1 and those are for the bigger guys so for mid sized and small guys larger is 5 7 hence you do not need V cause is a very small board (mine is 5 2 )

The Fish is so skatey that if you put a V finish too slide (y) and lose hold and speed.

There are other parts you would tweak to shape a modern fish; but seems that all are very busy building old fishes with wrong rails and keel fins…

-The bottom depends deeply on the surfer s skill. If you are “plastic” flow good surfer that use a HPSB; a concave between the fins would not interfere could be good for some maneouvers.

Waves are not subtle so no subtle changes, when you put a concave should be deep if not is like not putting anything, Like a V etc.

Double concaves are in reality one of the V bottoms. There are three V bottoms (flat, convex and concave) if not are channels actually.

I use a Bonzer style and the shape is faster intrinsically.

Most of the boards that I shape have flat bottoms and in some ranges; a V bottom in some part of the last 1/3 but I use plenty of tail rocker and in some range; a kick in the tail.

I like to put thickness onto the middle of the board (all along) so the surfer can crank it up with the rear foot to carve down and go to the pocket with a powerful turn.

Lastly I have been having some trouble, due to lack of good surfers showing here so plenty of orders to the surf shop or to beginners.

\m/ \m/

To be honest, I feel like 30,000-40,000 is about the “master” level requirement.

Re fishes, in the fishes/vee discuss, I have measured/templated 3: 1) 6-6 or so Junod that a friend had, 2) 6-3 Mandala that I bought used, and 3) a Haut that was on site (for ding repair) recently. I can’t recall for sure right now, but I think the Haut had vee (no recollection on the Junod off the top of my head, but I have it in notes), but the Mandala stuck in my memory because I was surprised to find that had no vee at all – all single concave, through the tail tips. The Mandala stands out to me because of his connections to some established originators. I was surprised when I measured and notated it that it didn’t have any vee because it was very saucery to ride. But, of course, the fact that the one I had lacked vee doesn’t mean that other Mandalas didn’t have some. I remember nothing really about the Junod other than that it was red. I didn’t like it. I have the notes, somewhere, though.

I do think that even at the master level there is a lot of shaper-specific absolutism that isn’t grounded in any reality except their own, particular to their bodytype, surfing history, current ability and physical status, and abiding convictions.

I rode a 10 footer made for a friend of mine, recently, made by a shaper who is very “hot” right now, one of the 5 or 7 most visible names in shaping, arguably. It was a hull with a step deck. Not only did I hate everything about it, but I couldn’t catch well-shaped waves on it even though it was made for a guy 20 lbs heavier than me (catching flat-faced, juiceless mushballs was much easier). I love the way that shaper surfs, like him as a person, and thoroughly enjoy sharing the line-up with him because he’s a thoughtful & considerate person (i.e. he lets me have my waves, positions to work together when I’m on a smaller board, etc.). Conversations with him have influenced some of my development greatly. But I hated that board my friend got from him and hope I never see it again. It was even uncomfortable to lay on for both the friend & myself because of how the step-deck was executed. The friend he made the board for surfs 9-11 foot quads mostly, of his own making, beefy Brewer-esque boards with fatboy rails and thiiick foils. The famous shaper told him, when they were discussing what to make, that quads just don’t work on longboards. But, OTOH, he has also told me directly that he doesn’t lay out his own fins, just sends them to the glasser who makes those decisions for him (even after shaping, I guess, thousands of boards). I’m sure some on Sway’s will agree with that shaper about quads on LBs, and others will think it’s a ridiculous position to take, yet am also pretty sure that across that divide the level of shaping expertise of the opinion holder are not much related to the opinion held.

I’ve ridden the friend’s self-shaped quads. I like them better than the famous shaper’s board, too. I don’t remember whether the well-known shaper looked at any of the bud’s own self-shaped boards, but probably if he did they would hurt his eyes and permanently scar his soul.

Well I guess so.  Stating the obvious;   Never seen a Brewer Gun without his classic Single to Double and V.  If you do a little research,  you’ll see what I mean.  For myself;  That’s about as cluttered up as I would ever want.   No Bonzer or trenches or channels in anything I Shape.  Mostly single concave to soft V or reasonably flat.  Always depends on the shape.  Case closed.  Phedus you are sentenced to to 30 days in the hole.(E&B)

I think it very much depends on the style of the surfer and the fin setup.   Front footed on a thruster needs something different than rear footed on a thruster.  Singles where you’re letting a longer rail line do all the driving needs something different the HPSBs where you don’t have the length or the straight lines in the template to drive off of.

TO ME, straights for speed and curves for control still seems like an applicable rule of thumb.

I think the original question was about short boards, not guns or long boards. My answer was about shortboards.

Yes, but the obvious is that the Brewer bottom is in some way incorporated in almost every Shortboard Thruster or Quad in every Surf Shop.

So what I have here is a basic flat bottom in the forward 2/3’d and then—-/

V in the Tailblock.

Modern “Chine” Rail.  Tucked Edge  below the Apex.

Directed at nobody in particular.

Structurally – concave should make the board thinner while helping to preserve stiffness.

A venturi channel (concave?) increases pressure before and after the narrow section.  Water is moving faster and at lower pressure while traveling through the narrow section.