# Another concave question

Hi all,

is it a valid concept to keep the decrease of area from the widepoint back to the fins small by adding bottom contours?

I know, concaves and channels have been done a million times, but i have never looked at this from that angle.

For instance, do you look at your cross-section and decide how much bend you need in the contour to mach the crosssection of the widepoint?

For sure, the area will decrease at some point, but just as a concept to follow.

( i read a copy of naval architecture and was struck by the parallel outlines concept)

Happy new year everyone,

best wishes

J

I’m not sure I understand what you’re getting at…

I provided a link to one of Ryan Burch’s sites that shows some of his boards having a reverse curve (hourglass-like) in the outline behind the mid point. The curves are similar to Meyerhoffer/Mackie/Mirandon outlines.  I think the basic idea goes back as far as Simmons even - he used parallel or nearly parallel sections in some of his outlines as well as concave bottom contours.  Again, not sure if that’s the sort of thing you mean(?)

On shapes I’ve done I tend to follow my instincts and put certain design features in positions that seemingly will work together… I.E. most prominent tail rocker curve approximately where the ‘hips’ in the outline are and place sidebite fins accordingly so the board will have a defined pivot point.  On some boards I will add a roll ahead of that area and concave(s) through and behind that area with the intention of providing a ‘squirt’ effect on bottom turns.

To add to the equation, it is interesting to lay a straight edge diagonally through a tail concave and see that with certain designs, a dead flat area will occur where the concave and tail rocker are combined.

I think it is important to differentiate between “area” (X,Y - sq.in. - 2D) vs “volume” (X,Y,Z - cu.in. - 3D) - if the outline is the same, removing foam by introducing concaves is going to reduce volume.

I’m gonna stop there since I’m not sure if I’m even remotely on track.

On most planshapes you couldn’t add enough concave to match the surface width at midpoint.  Why would you? I mean, how are you relating that to performance?

You lost me at adding contours.

As I see from your responses, its not a valid concept.

Actually I dont know too what track i am/was on, making that thought public helped me to dump that idea faster.

Thanks, best wishes