question about board concaves

[IdRatherBeSurfing]

do they make a big difference to speed etc?? neither of my boards have concaves not even my shortboard. i spose it wouldnt make a difference at the level i'm at any, can hardly ride the damn thing yet!

[Phil]

yes they make the water flow faster under the board so they go faster

[kitesurfer]

A concave flattens out the rocker through the centre of the board as phils says allowing the board to travel faster. For once he's got it right!!

KS

[drowningbitbybit]

do they make a big difference to speed etc?? neither of my boards have concaves not even my shortboard.

Are you sure your shortboard hasnt got concaves? They're usually very subtle - you can barely see them. Put a ruler across the flat of the bottom of the board (near the fins is easiest) and see

[drowningbitbybit]

That useful 'know your surfboard' site


...But the pictures of the concaves are exaggerated!

[surferdude_scarborough]

as someone whos just got a new board with concaves. yes

[Tom-Irons]

I think it adds to the streamlined effect so i goes faster.

[drowningbitbybit]

I think it adds to the streamlined effect so i goes faster.

No.

It directs the flow of water between/around the fins. Which isnt the same as streamlining.

[tomcat360]

Don't forget with a nose concave you get a more extreme "gas pedal effect" when you go to trim. My recent board I put in a nose concave to flat mid to vee tail, should be fun.

Lots of shorties have a single to double, with it breaking into two infront of the fins. As someone already said, take the fins off, put a ruler on its edge, and look down the board, see?

[Otter]

I've got a 9'6" carbon fiber Walden Magic Model. It has the concave from about mid board to the tail, with the tail slightly bumping at the skeg. This board can really hold the face and I'm convinced that it moves faster than my other non-concave boards. It's a pleasure to manuever as well. I'm a firm believer in the concave.

[surfsc77]

if your a beginner you probably dont want that much of a concave anyway, depending on whta kind of waves your riding. if there smaller waves, then ive found that i like a less of a concave.

[RJD]

Concave either provides lift (as in nose concave) or channels for speed(center concave).

Nose concave gives lift for nosriding similar to an airplane wing but makes it less stable and harder to ride (on the nose).

[kitesurfer]

Concave either provides lift (as in nose concave) or channels for speed(center concave).

Nose concave gives lift for nosriding similar to an airplane wing but makes it less stable and harder to ride (on the nose).

The lift required for nose riding comes from other design aspects of the board which are less obvious than a big nose concave.
To be able to ride the nose well you need a board that the tail will not lift out of the water. This is achieved by reducing the pressure around the fin by either lots of tail lift or a rolled bottom with soft rails.
Of course as with all board design it's never quite this simple. Many nose riders do have concaves, but can be at the expense of the overall performance of the board. Nose concave will (because it forces the water to slow down as it changes direction as it passes over it) create drag which will slow the board down. This can be good for nose riding as you don't want to out run the wave, but this is not good if the tail of your board is still travelling quickly as it will want to outrun the nose causing the tail to slip out, so you need to slow the tail down, more rocker and tail lift again.


KS

[IdRatherBeSurfing]

Are you sure your shortboard hasnt got concaves? They're usually very subtle - you can barely see them. Put a ruler across the flat of the bottom of the board (near the fins is easiest) and see

definitely sure - just had another check! its flat bottomed

[RUSS-D]

Here is what I have learned about concaves. A single concave throughout the length of the board will suck it to the wave. Meaning it is great for steep, barrels, and vertical walls. Double concave will give you lift, and speed in a wide variety of waves. Most shorties have a cross between the 2. They start out with a single concave, and flow it into a dbl. concave. But this is stuff I am just learning about. Thought I would share it .

[kitesurfer]

Here is what I have learned about concaves. A single concave throughout the length of the board will suck it to the wave. Meaning it is great for steep, barrels, and vertical walls. Double concave will give you lift, and speed in a wide variety of waves.

I'm curious russ where did you read/see this explanation?

KS

[TicTac]

Here is what I have learned about concaves. A single concave throughout the length of the board will suck it to the wave. Meaning it is great for steep, barrels, and vertical walls. Double concave will give you lift, and speed in a wide variety of waves.

I'm curious russ where did you read/see this explanation?

KS

Your not the only one kitey Not entirely sure but think you've got concaves confused with how far the bottom rocker extends past the center point of the board.

[Laguna]

Are you sure your shortboard hasnt got concaves? They're usually very subtle - you can barely see them. Put a ruler across the flat of the bottom of the board (near the fins is easiest) and see

definitely sure - just had another check! its flat bottomed

Maybe you have a single concave which fades to flat. It can be hard to see sometimes

[Jimi]

Another point, the single concave (if it's deep) may help direct air under the front of your board, and thus reduce skin friction over the entire under surface of the board when it is flat on the water.

I'm not sure how much difference this makes on a shortboard, but on some quirky australian designed sail boats this effect is utilised to good effect, and some hydroplane racing boats of the 60s used concave hull shapes to generate aerodynamic lift (as separate from hydrodynamic properties).

[Driftingalong]

If you want to get real technical; it's based off of Bernoulli's principle.

http://home.earthlink.net/~mmc1919/venturi.html

The link has a good explanation of it (leaving out all of the math equation stuff; there's a link for that too at the bottom), plus a cool interactive animation.