bottom contours

Hi I’ve made 8 boards now but all have been flat bottom, the reason is my knowledge on cutting in bottom contours is very limited, would anyone be able to enlighten me eg how deep do you cut for a single/double convave, do you just mow down the centre and then blend in,where does the concave end and the v begin, how much v etc. Any help would be cool. O.

O, I found this thread by searching for “how to make concave” in the archive http://www.swaylocks.com/discussion/archive/index.cgi?review=5972

This (page) links has a good description of concave bottom contours for short boards, but no advice on how to put them into a board. http://www.naturalcurvesboards.com/html/designhtml/bottoms.html My experience has been that the best way to put concaves into a bottom are with a planer or whatever tool you use to do your major work. Once you’ve “skinned” the bottom of your blank and established a flat surface side to side, determine where you want your concave to begin and start “banding” from rail to center from this point. Make each band as you move to the center of the bottom a little bit deeper than the previous band. Repeat the process from the other rail to the center. Repeat the process until the concave is the depth you want. Plan ahead. Try to anticipate how much rocker this may add or take away from the design of the bottom of your board. You can clean up the planer work with a block plane or a surform. You could then finish this area with a flexible sanding block. Try making a sanding block from a piece of high density foam - about 10" long x 2" thick x 3" wide. Run the block through a mider box and cut down from the top of the block on 1/2" intervals stoping the cut 3/4" from the base of the block. If you press the block into your concaves with a piece of sandpaper or screen the block will flex to the contours of the concave. Push the block and paper into the concave and pull the paper and block through the concave to finish the surface. Most concaves have a maximum depth of 1/8" to 5/32". Higher volume boards probably work better with shallower concaves. Lower volume boards can tolerate deeper concaves. Since concaves may feel like they trap water under the board as the board runs or travels along along the surface of a wave it’s probably a good idea to have the concave get shallower as it runs through the tail and out of the board or to add a little vee in this area. You can do this by adding a little rocker in the rail.