My most recent build was a 5’-11" light wind kite surf board based on the Tomo Vanguard style board. This board was wide (22"),quad fin & had a deep single concave thru the length of board and the maximum depth at the middle of the board was (~7/16"). While this board did accomplish my main objectives of planing quickly & still being loose on the wave face, there was an unintended consequence in that the board bounced or “slapped” the chop when sailing out into and thru the wave zone. It became painful on my middle aged knees & low back.
On my normal to high wind boards, I usually design less single concave in the middle at (`3/16") and add flat “V” in the nose & tail. This tends to “soften” the ride but still turns well on the wave face for me.Early planing is not really a concern on that board.
As I’m just an amateur “garage hack” (with less than 20 under my belt) that enjoys building boards, I’m here asking for advice from the more experienced shapers out there. How does changing the depth of a single concave affect the ride chartacteristics of a board? I understand that rail profile also affects how it will ride, but I’m trying to learn how changing just the depth of concave would affect the ride. In the words, If you have two boards with identical rails, but one has a deep single concave & the other a shallow concave, how would they ride differently?
Recently watching some old Maurice Cole design vids so immediately thought of that. If you add reverse vee aka eev you might be able to keep the deep full length concave and it’s virtues and dampen out the slap and bounce. Just make the concave “spriral vee” to single concave, with the vee apex under front foot. Link below goes to short ride report/review by Nick Carroll
Possibly drifting off topic… a dual concave board I have (pic) with fairly deep spine(?) along the stringer can get a bit slap happy. It’s particularly noticeable in chop or ‘rebound’ waves at spots with a steep beach or cliffs. Of course any board will take a hit on severe rebound waves - Makaha comes to mind, but I’d think that any sort of bottom that funnels the water flow will be more prone to this occurring. The deeper the funnel, the worse the problem.
John- i totally agree with you. It appears from your picture that the board basiclly has a double concave through the middle. I’ve never been a fan of double concave even back into my windsurfing days because of how “slap-happy” they are. To me, it’s the same as the two types of ski-boats. A single hull “v” power boat rides relatively smooth through the water even if it’s choppy. You go out in a tri-hull ski boat in the same conditions and you get the “slap-happies”.
But going back to my original (?), how does cghanging the depth of a single concave change the ride characteristics of a board?
When flat more you speed more concave lift board, less contact with water more bounced in chop. Harder to control and to initiate turn even more if board wider.
When on rail more concave give more rail grip in wave = more drive = feel of security so you Can push more and have more speed and projection but need more action to lock out rail so Can feel tracky. But here more than deepness at center it’s rail profile that play so you Can have a center part flat with curvy at rail profil concave, like a camber, wich give high grip on rail and less lift on flat. A slight double in a single give same profil : deeper part of concave near rail so more angle at rail.
