I have been reading the archives on theory of concaves and how they create “lift” by directing water/air under and through the board. In my reading, I haven’t found anything discussing the transitions in and out of concaves. Can anyone help with a basic question? First, it make sense that as you move out of a concave area towards the tail that the transition be smooth to reduce drag and assist water flow, but what about the transition into the concave from the nose? Is there any reason this needs to be as gradual as the transition out? If you think about an airplane wing, the transition into the concave could be much more abrupt than the one out. Has anyone experimented with something like this?
Here are my thorts, I’m a registered civil engineer (U of H '77) with some formal undergraduate and graduate level fluid dynamics training. Newton’s Law tells you that it takes energy to change the position or velocity of any mass. In surfing, energy (board speed) is only available by surfing “downhill” on the wave. Turbulent flow is a great way to dissipate energy - engineers encounter this when designing drainage culverts, particularly steep drains. Transitions in bottom contour may require less energy as long as the transition does not induce turbulence. That said, I think most of the fancy bottom contours one sees are a real hassle for glassers and are mostly marketing CRAP. Few are able to concentrate on the simple aspects of board design (plan shape and fin placement) with all the full color crap that’s promulgated by magazines, marketers, most shops and so on. As mentioned elsewhere, a hot surfer can make a door look good - too many of us blame the equipment for our own shortcomings. Shoot, what a rant.
Charlie, thanks for your rant. I really just curious how abrupt the transition to a concave bottom from a flat or vee bottom can be. My thinking is that at some point the abrupt change will create too much turbulence and negate any “lift” you might get from the concave. But I am just starting to shape boards and don’t have any experience to back up that thinking. Was just wondering if anyone has experimented with really abrubt bottom changes like I describe.
Hi Bart, about 15 years ago l played with what you are talking about, l made myself a board that l called the “crater”, l shaped two hard edged deep concaves, one between the feet and the next one about 12" up from that one, l didnt take them all the way out to the rail because l knew what effect that has, especially up front, my main aim for this project was to see how the bottom would react with major dips and hard edges through the stringer and verify my theory of the major reaction key of a surfboard being the outside rockerline, rail shape and edge placement, every thing else about the shape was what l normally do for myself, surprisingly it went quite good and l rode it for about 6 months having a few great session on it at Kirra, what l did notice was that every now and again it would do something funny like suddenly stop going forward or pop out of the face up front and it didnt grovel that well, so l figured that for the effort of the shaping and the arguments with the sander it was’nt worth persuing, but you might find it different, dont ever cast an idea off until you try it yourself because that is why we shape our own boards - to make them go the best for us, if someone else likes the way it goes’ you might have to make them one. The fun begins KR
A label here in Australia called Island, of Philip Island in Victoria produced boards in the late '80’s with a concept similar to that described by KR - The boards had six steps in the length of the bottom, like grater scoops either side of the stringer- the concave tapering off before the next step . I never rode one, but some locals rode them with great sucess. If you are super curious you could contact Matt Ryan or Tom Tyrrell C/O www.islandsurfboards.com.au http://www.speedneedle.com.au
Bart: You might want to take a look at a board created by Ben Aipa called the stinger. The board has a break in the rail similar to a wing but further up towards the center. The rail break continues across the bottom to create a step down in the rocker. As I recall the board was used with success by one or both of the Ho brothers in pro contests. Again, as I recall, it was regarded as a good small wave board because of its short turning radius. Patrick
Thanks for all the input. I am just getting into shaping and this site is a godsend. My goals as a new shaper are: 1. Enjoy the process. (You only have so much free time, you might as well enjoy it.) 2. Shape boards that you won’t see for sale in the surf shops. (Search for quantum leap improvements in design, not minor tweaking of the current standards.) This site is a big help on both counts.
hi Bart, where are you from? Bart sounds euro?
I happened to read your interest in doing a little designing out side the box. As you put it"Search for quantum leap improvements in design, not minor tweaking of the current standards." I have been working with some new innovations particularly in the area of designing using only stright lines. Taking my “razor” rail from the 80’s and using a stright edge for a template,designing around geometric angles rather than arcs.The bottom has a major concave from nose to tail.The water flow to and through the concave is only in relation to the angle of the board.And the only curve in the board is in the rocker, everything else is a stright line.To be sure a shapers and glassers nightmare but something has to change!We have only been re inventing the wheel for decades.Good luck…aloha, Steve