Considering adding shallow double concaves tapering out just before side bites on a 9’8" I’m shaping. Is anyone riding or shaping these into their longboards? If so, how do you feel they affect performance,speed etc.
Appreciate any feedback.
A few years back I broke an EPS HP longboard that had a deep double concave through the middle. Worked best as a 2+1. Could really rip turns, do floaters, etc. Not as good at noseriding, though. I took out 2+1 setup and put in a long Harbor fin, and it noserode better, but not great… had a tendency to suddenly drop from the high line down to the base of the wave when out on the tip trimming through steep sections. I guess it couldn’t handle the severe trim angle… needed to point more toward the beach. Logs noseride so much better, with simple, rolled bottoms.
any feedback, so here is mine (I never surfed a longboard with concaves)
From a hydrodynamic point of view:
Concaves will increase the lift of your board right above the concave, due to higher pressure. This will lower the noseriding ability if the concaves are back from the wide point. If you want to compensate the pressure rise make them converge (like a bonzer). (unless you go hypersonic then it is the other way round)
The speed will increase until you reach the point where the bottom is flat seen in side view (perpendicular to stringer). When you go deeper speed will decrease in comparison to flat.
remark: bonzers create more lift due to the placement of their sidefins (effect is displayed as “use of otherwise wasted energy”)
Aloha cleanshape:
All of the performance longboards I shape have bowled double-barreled concaves on them, where there is a flow through single concave running into the doubles and then with V out through the tail. I position the concaves so that they are at their deepest right where the side fins are positioned. I have found this setup to really enhance the performance of the board by giving them a lot of extra squirt and faster out of the turns. Mine are very deep and the key to them is the bottom of the concave is moved out closer to the rail. Between the concaves the bottom has a bowled shape to enhance rail to rail transitions.
I shape the V in the tail first and then add the double concave so that I get the bowl higher than the rail.
My experience using this bottom configuration for the last four or five years is that they enhance the overall performance of the board. I have not noticed any loss of nose riding ability in these boards with this configuration, which I attribute to the interaction between the side fins and the concaves. I leave the rails very hard where the concave meets the rail.
Most of my performance longboards are in the 9’ to 9’ 6" range but all of them have this type of bottom.
Certainly adds a whole new level of speed to the board. I personally would not ride a longboard with any other type of bottom especially not if I cared about overall performance and speed.
The biggest issue with them is placing them correctly and then blending them into the other elements of the bottom, they can be tricky to get right but are worth the effort in my book.
These days most of my boards like this are quads as that adds another level to the performance. I personally find that I can nose ride a quad better than a single fin, as blasphemous as that sounds, maybe it is just me!
Thanks for response. I'm going with the concaves, slightly angled to match fin toe-in.Hand-Shaper-- nice website.