This is probably an ancient thread that I’ve stumbled upon but the statement about single concave not flattening or straightening your rocker and only the rail rocker changes is completely wrong.
The method that Bill (Barnfield) and the vast majority of established shapers use was particularly influenced by Bill’s creation of ‘the rocker stick’ and how we used the straight edge along the bottom to measure and quantify bottom curves whether it be staged or continuous bottom rocker lines. Use of a rocker stick, using center of the bottom as a starting point, gave us a common language that we could and can consistently reference to.
If you take nose & tail rocker measurements using a rocker stick before shaping in single midship concave, then remeasure after doing so, you will invariably note a flattening of the rocker at nose and tail. Or to put it more correctly, those measurements are still the same as they were before shaping concave into or near the center, but the relationship of those curves has now changed due to the changing of the curve thru the center of the board. IOW, if you scribed the bottom rocker before you added the concave, then used the changed center stringer rocker as a comparison, they now relate differently to the nose & tail rockers.
The addition of the concave or concaves. also has a relationship with the finished foil of the board. It helps to envision the entire board as having what Bill once described as “lines in space” and how those lines interact with one another and as a whole.
Surfboards are comprised of ‘compound curves’ and, for many of us, it is the challenge of successfully combining all those beautiful curves that keeps us addicted to shaping.
The vast majority of shapers feel that deck rocker is a result of bottom rocker. I don’t agree with that and I have heard vehement arguments that because we shape the bottom first, the decks are just a consequence of what we do to what many feel is the most important part of the surfboard.
The majority of shapers will cite bottom curve as the ultimate line that is traveling thru the water. I would agree, but only to a certain extent, because as a surfboard designer, if I only look at it that way, I will be heavily compromised in creating rides that are fresh and different. Deck rocker is important because its relationship to bottom rocker creates the foil of a surfboard.
A surfboard is a foil and has draft as it moves thru air and water. Deck rocker affects the ride significantly to a surfboard and it is incorrect to hold the supposition that all surfboards with the same bottom rocker curve will ride exactly the same regardless of its deck rocker. If this were the case, a step decked longboard would not ride differently than one w/o the thinned step deck, nor a Surfski with it’s very thick tail.
When you understand then master creating foils, you can create different balance points for a design that gives the board more lift in one area and more or less resistance in another area. Foil and draft, lift and resistance all contribute heavily as to what a surfboard will ultimately do.
Finally, as far as your gut feeling to try a “Hypto Krypto” type bottom, I would agree that’s a good example to follow. Hayden’s bottom design is very similar to what i put into my first Fountain of Youth models nearly 30 years ago. I still use that combination of contours in some of my boards today, and guys riding them describe it as a hot knife slicing thru a stick of butter. Here’s a “Rincon sled” I just finished for a buddy that opted for an 8’0" to help him compete in the lineup. It has the bottom formula I mentioned previously.
Keep on shaping!
BF
