Concave questions

[alex85]

Hi everyone, big injuries lead to a long time off the water with free time to spent somehow, so I would try to realize what came in my mind a long time ago:building a twin tip.

Searching here and there I found a lot of infos but one remains in my head, how To Make concave?

Any another help Will be appreciated cause I'm a totally beginner and On the moment I'm studing the different type of material...

[rynhardt]

Any particular reason you want concave?

Do you think it will make the board track better? (only when ridden flat)
Absorb chop? (concave will make this worse, when ridden flat)
Strengthen the board longitudinally? (maybe, but board thickness and material choice plays a big role too)
Edge better? (nope, rail design will have a bigger impact here)
Prevent spray? (maybe, but board length and tip design plays a bigger role)

Oh, and the above are just my 2c, not gospel.

[rynhardt]

One example of a production flat-bottom board is the CrazyFly Allround

[Blake]

Concave works great!
Look at the Mako from Ocean Rodeo, they have been making it for over 10 years now....with concave!
Concave smooths out the chop.

My homebuilt board has concave and it rocks in chop!

[alex85]

Any particular reason you want concave?

Do you think it will make the board track better? (only when ridden flat)
I was thinking it tracks better every time

Absorb chop? (concave will make this worse, when ridden flat)
ok but in % how much we ride flat?

Strengthen the board longitudinally? (maybe, but board thickness and materiale choice plays a big role too)

Edge better? (nope, rail design will have a bigger impact here)
I think is related to the first point, then right question is:a board with the same rail design edge better with or without concave?

Prevent spray? (maybe, but board length and tip design plays a bigger role )
Same as above:a board with the same lenght and tip design prenvent spray better with or without concave?

Oh, and the above are just my 2c, not gospel.

I always felt better with board with concave vs flat bottom but it can be due the specifics boards I've Tried so in my mind cames put and idea like with concave better than without.

Also, by my experience board with concave land softer than board without.

[alex85]

Concave doesnt flat the rocker in the Middle of the board resulting in a board that works like a flatter baord without the spray of a flatter board?

[alex85]

My idea is more like this than an eliptical concave

[downunder]

Well, if that is your idea for a first DIY board, good luck with it!

Seriously, if you've never built a TT before this is a waaay advanced build. So, you are not after the concave but the channels...Wrong subject line.
Wish I could help, but after many boards built I stay clear from channels. To much effort for small gain.

Good luck

[Johnny Rotten]

There are a number of ways, I've pretty much used em all. Depending on complexity and bottom shape.

Pre form the rocker. then carve out what you need on the bottom for concave and glass. This is typically done with surfboard blanks. stringer and foam cut results in preformed rocker, concave is shaped out usually using a planer if you are serious sanding blocks if kicking it ghetto pretty much anything that'll mow foam. If you are starting with a flat piece of foam you can always glass and cure the top first to get the rocker you want and then cave out the bottom in a second step.

For simple single concaves where you are shaping the rocker on a rocker table you can add concave to your rocker table. my rocker table has aluminium skin on plywood if I stick something between the aluminium skin and the ply wood and weigh down my part (in addition to vacuum) I get concave and rocker in 1 shot but is limited to single concaves.

If the concave is more complicated (dual concave or channels) and you are making from a flat piece of foam you can get rocker and concave in 1 shot.....vacuum bag the entire board then selectively weigh down the parts of the board which are not concave in order to make the vacuumed board take shape to your rocker table.

you can also pre shape the negative of the concave you wish to have coat in release agent and vacuum your board down onto that.

[downunder]

^
Slingshot is all wood. Same as this board stolen from me last season: