diagonals

General Discussion
1

I was reading an old thread with this photo posted by Blakestah and it got me thinking. Every underwater photo I’ve ever seen is similar- with that sliver of the surfboard that is in contact with the water.

Instead when we design surfboards we don’t think about that sliver (or at least I don’t or never did). We agonize over the whole outline. And the entire foil , nose to tail.

Instead, looking at that picture I imagined a concave starting at the rail, cutting diagonally across the board, opening up at the tail. Of course, then you have to have an analogous concave coming the other way, from the other rail, crisscrossing. I think it’d look almost like a backwards bonzer bottom, double to single.

It got me to thinking back to when I was lofting sailboats. Yacht designers work with varous sets of lines- waterlines (analogous to our outlines), buttocks (yes boats have buttocks, analogous to our rockers). But yacht designers are also aware of the fact that boats almost never sail flat. So part of their design process are lines called “diagonals.” You see them in the drawing of the boat looking at the bow and stern ( Diag A, Diag B, Diag C). You see them again at the bottom of this drawing, going the full length of the boat. Surfboard designers have nothing analogous. When I worked for a boat builder (Dencho in Long Beach) lofting lines drawings, we used to go back and forth making sure the diagonals were fair (smooth, no bumps or hollows), without distorting the water lines or buttocks (yes boats have buttocks).

So what I’m thinking is that surfboards designers should start thinking about the sliver. And maybe surfboard CAD programs should have functions to plot out rocker/bottom curves at various diagonals across the board and start analyzing what effects manipulating the curves that flow with and across them will have.

I don’t know. It’s just an idea. Thinking about it, surfboards are far more complicated than sailboats in their dynamics. Boats don’t have to go rail to rail! But we still could learn a lot from other disciplines.

2

llilibel,

I have a feeling your next board is going to be some kind of hull. I’ve got a stripped longboard that I’ll try your analysis on. Hope your feeling better. The Cove has gotten a bit zoo-like of late, I think. See you soon I hope.

Ride on,

Tom

3
Quote:

surfboard CAD programs should have functions to plot out rocker/bottom curves at various diagonals across the board

I’ve had a standing request in for that function for a few years now (or at least longitudinal slices away from the stringer) - sure would have prevented a few cases of ‘bunny ears’ over the years where slice transitions didn’t go quite as planned.