Hello everyone,
I have attached a photo with three masterpieces showing some single concave drawn onto a board (rocker view).
theoretical question: (and assuming the length of the single concave cant be increased.)
1). would the limit of single concave depth be where the rocker would become flat? (middle picture)
2). anyone ever done concave so deep it inverted the rocker curve? (third picture)
3). how I assumed single concave was shape, maintaining a smooth rocker curve only flatter than the rail rocker. is this correct (first picture)
how should single concave look when shaped into a board (rocker view)
My main thought is: In the most general of ways, concave is “usually” towards/in the rear - at least through the fins - and, as I think about some of the hpsb’s I’ve looked at lately, some concaves seem to run about the full length. Mostly like drawing #1.
I’m not an expert, but I think, you are answering the wrong questions. The first question you should ask, or answer if you already know, what do you want the board to do and do I need a concave for it and the then following, how should this concave be designed.
As far as I know the purpose of a concave is to lift the board while speeding. So if you want a noserider you put the concave in the front. If you ride your board from the tail and want to decrease water resistance, you put the concave(s) in the tail. A concave in the middle section should lift the board evenly, but front and tail, if convex will work against it. So finally your concave needs to be designed, for your objectives. And if you flatten the rocker, you will get other parameters coming into play. As far as I understand the science behind it, the flatter the rocker or even concave rocker) will decrease manouverability or turning capacity, but will increase paddling speed.
For my boards, I’m an older guy (50plus) I need paddling speed, everything what helps me to paddle easier is appreciated. So I usually design a concave in the front to decrease water resistance while speeding, blending it into a flat middle section with a rather flat total rocker and blending into a convex tail, combined with a lot of volume. The results should be boards that fell like short longboard, but paddle easy and allow me to ride the face of the waves. Pro manouvers like aerials etc. are not an objective, I can not do them anyway… 
The most important thing on a surfboard is having the rocker and foil match the curves waves you intended it for. Bottom contours are used to modify or control the existing rocker and foil.
simply put, bottom contours change the angle of attack on your board
Ive found deep single work best for me in waves coming out of deep water, Indian ocean reefs, waves you cant see sets coming in, etc. I dont think they work the best in slower californian waves, although its not terrible. The deep single(1/2’‘-3/4’') allows the board to square off the bottom turn with a deeper and tighter arc. More squared bottom turn allows for a more aggressive top to bottom approach attacking oncoming sections and lips.
from my experience, I think a deep single works best used on narrower boards (<19.5’‘) shorter than 6’3’’ with a slightly rounded deck. Im about 5’11 145lb for comparison. Boards that are longer or wider Id prefer a forward Vee or double with a flatter deck to help it tip side to side. Possibilities are endless
There is wisdom in the words written by
TaylorO, Surfdude and tonybanger.
IMHO…
- The concave goes under your feet.
- The deeper the concave more power/energy is needed.
- Don’t mess up your entry rocker!
