Been reading a huge amount, specifically from Mike Daniels regarding wider boards and single concaves. I keep my boards to 2 inches with boxy rails and find i could use a little more bottom rail to turn off (using 2x25mm sheets with the rocker glued in) . I had planned to put some concave in my next board - outline will be similar to the CI neck beard, single concave through to the tail.
After reading mikes posts will keep the concave to the middle of the board and not 'hook' at the rail. So my concave will probably run in the middle 16 inches of the board and be super shallow and the deepest 1/10 of an inch (remembering small overall thickness). Using a large square tail of 8 inches which will mean the 16 inch concave will hit the rails infront of my side fins. Will be almost flat again as it goes through the tail.
Board width is 21.5 inch mark by 5'11
I have tried to draw a cut section of the rocker plan to gauge some thoughts of would this help get a thin board turning better rail to rail and a little lift, i have kept my boards flat til now but find it limits it to the size of surf you can ride, lots of skipping off the bottom turn.The red areas are where the foam would be removed, I was thinking i would keep the taper at rails matching the depth of concave as it runs down the board.
I usually follow the outline with the concave, but doing it straight 16'' wide down the middle will give you a wider panel off the concave forward - and it will run out the tail to get the bite back there. Sounds good to me on a 21.5'' wide board. The slight roll into rail will help the board ''roll'' onto a rail to initiate turns.
.1'' isn't much, though. Keep in mind that your laps (I assume you're hand-lamming) will ''add'' some concave.
Sorry I meant with regards to the total board thickness so 1/10 of 50 mm which equates to 5mm max depth in concave deepest part will be middle (between feet.)
5mm should be deep enough? or fractionally deeper in the middle? - i was thinking run it straight as it will still give me flats to take advantage of the advantages of a flat bottom.
I will start my roll around 2 inches from rail and follow the outline.
I think keeping it straight will be easier to hand shape for a novice as well.
5 mil is more like it, and I'd put the deepest part right on front fins (provided you have a decent bend in rail rocker at that spot).
Just a little roll outside the concave will help a lot in getting the board on a rail. You can tape off the line between roll and concave when you fine sand, that way you can block away (diagonal on concave, end-to-end on roll) without worrying.
Bee - Mark Rabbige does something similar, in that he uses to parallell rail chanels on each rail diring the middle third of the board - he steps it down from the rail to help the ro;; from rail to rail.
beerfan, thanks for keeping that question ''general''. In those terms, forward concave would be for paddling, rear concave for turning. The deep rear concave is more suited to hpsb, the forward concave is more suited to higher-volumed boards.
tommy, on wide and/or thick boards with concave, having a little flat or roll outside the concave will help the board ''roll'' onto a rail. Almost every turn starts with getting the board up on rail.