How do I know what kind of concave I want on a shortboard (tri-fin) designed for small to medium waves? (When is it appropriate to use single, double, or triple concaves?)
Thanks
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How do I know what kind of concave I want on a shortboard (tri-fin) designed for small to medium waves? (When is it appropriate to use single, double, or triple concaves?)Thanks
There’s a kazillion variables.
If you start flat, and consider how the water flows under the board, you can get some idea of what water does, and how the bottom contour impacts this.
Surfboards get some lift from planing - that means the bottom of the board re-directs water down, and the counter-force supports the rider. Now, water doesn’t really like to go straight down, it would just as soon go sideways. If it goes sideways instead of down, it doesn’t generate lift.
A major thing bottom contours do is bias water to go down instead of sideways. Water under a surfboard, relative to the board, goes towards the tail, towards the rail, and down. It goes towards the tail at the water speed. The movements down and sideways balance each other. If you use a concave, you will make water less likely to move towards the rail, so it will go downward more, and you will get more lift out of the same hull. So, a single concave creates lift and planes higher.
If you have a Vee in the hull, it will make water move more towards the rail, and less downwards, and you will get less lift out of the same hull. The board will plane lower.
The most common concaves I see are single to double concaves. Single between the feet, and double, angled to the rails, in the rear. The rear concaves re-direct water for turns, while still creating lift.
THe “Merrick” style of concaves (maybe Webber created??) flatten into the tail to reduce directionality in the hull - to further loosen the tail for turning. Deep concaves or Vee are directional elements in the hull, whereas flat is less directional.
The way in which Vee or concaves translate into changes in the ride of the board is heavily dependent on how, exactly, they are done. But, generally, the single will allow the board to plane higher, and Vee will plane lower. Flat tails are looser, deep concaves or Vee in the tail add directionality. Rolled Vee planes lower, but doesn’t interfere with rail to rail motion as much as peaked Vee.
Virtually all high performance shortboards for small waves have a single to double concave, most flattening into the tail.
well put!!!
Drew
Hey,
What blaksta wrote was gold!
And like hey said there are a million variations.
Another one you could try that some of the pros are on to is going for a single concave with a slight vee in the tail to keep the board better from rail to rail.
Alot of its prefrence.
Josh,
PS… you’ll soon enough now all about concaves its was only a while back when i asked the same question.
Great! Thanks, that’s the answer I was looking for. I’m not a shaper, but am trying to figure out what I might want in my next board that will suit the conditions I think I’ll be using it in. Will probably go for the single to double concave.
blakestah - great exlpanation man, all makes sense now, as I’m starting out I’ve steered clear of concaves, because I didn’t understand them, will try to see a few up close to get a better idea but want to start to play with these at some point.
The beautiful thing about surfboards is for the most part everything works. I used to ride concaves and now you could not put me on one of them on most boards. I still like them on performance longboards, but then I rarely ride those anymore. It all works. Ablity means more than design, but design is so much fun. Like surfing should be.
im impressed blakestah …
that post , just seemed to flow real nice and was easy to follow …
and i was agreeing with it as i followed it …
one question tho???
i wouldnt mind getting you to elaborate on why you made this comment …
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Rolled Vee planes lower, but doesn’t interfere with rail to rail motion as much as peaked Vee.
i agree rolled v planes lower , but im wondering how you would characterise the last part of the sentence in real terms …
ive always found rolled v to really interfere with the ability to get a board on the rail especially at speed …
so there could be some other equation im overlooking or we may have made opposite conclusions based on the other variables in the board …
the only thing that comes to mind is how the peaked v feels somewhat awkward in the transition , where as the rolled v feels more neutral when the board is flat but then creates problems when you try and bank it at speed …
regards
BERT
Bert, I think you & Blakestah are saying the same thing. When I read his (to paraphrase) ‘rolled vee doesn’t interfere going rail to rail as much as peaked vee’ I had to think about it too. But you’re talking about ‘getting it up on a rail’ and I think he’s talking about going from one rail over to the other. Either one will get up on a rail easier than a flat or a concave, just like you said. But, like he said, a sharp vee will have a moment of instability in the middle of the rail-to-rail turn that a rolled vee won’t have…and therein lies the ‘interference’.