I’m currently shaping a 6’1" x 18 1/2 x 2 3/8. Approximately how far up from the front fins would I want to beging the single concave? How long should this cut be before it feeds into the double? Where do the doubles feed back to flat? Finally, should the concaves run rail to rail or should they be a bit narrower and suttle? Sorry for the multipart question, thanks in advance for any info. What little I know about board design keeps growing exponentially the more I read what you guys have to offer, thank you.
Do you have a triple concave in your quiver that you could use for reference? If you do, put it bottom up on your racks and run a straight edge over it (Hold it on edge so the straight edge runs from rail to rail). That way you’ll be able to see the high and shallow parts of the concaves. I don’t think there is an absolute way to do it. It is all what you like and get use to. I have always read and done mine where the deepest part of the single is just in front of your center point and the deepest part of your double is just in front of your front fins. Blended together, with the doubles ending just in front of the rear fin. I just started doing them where the board is flat under the front foot with the back third of the board having a single concave through the fins with a double in it going flat off the tail. For me it seems to work. Good luck.
i start my single concave just ahead of center, double’s start about 12" in front of front fins w/ deepest area right between the side fins. fades to flat off the trailer fin. keep your entry nice and flat.