Hey all - While planning for my most recent board, I meassured many of my older boards, and discovered some interesting things about rocker and kick and angles.
The question that came to mind is this: If you want to make a board very similar to another, say from a 6’4" to a 7’6", or 8’2" ect…, do you increase rocker porportionally?
My thought are not to, or you’d end up w/a lot of it. I put kick in @ 25% of lenght from tail, and I “discovered” a good angle when I draw straight line - which I use for the tail rocker (flat @ stringer) - from the tail to the kick point, and then a straight line from the kick point to the center line. This angle is the same on all the good boards I’ve made.
My question was though: When laying out the rocker and foil on the stringer board, If I shouldn’t just choose an amount of “lift” - how far “up” the point is from the bottom of the board I am laying out the stringer on?
My thoughts are: If I choose this spot, for now, it’ll make things simpler, and it makes since as it would decrease the “belly” rocker on a longer board, which is better for speed anyway.
Hope this makes sense.
If it’s a straight scaling of a specific design, I use a proportional scale for the rocker. I also do for the thickness to keep flex similar. On outlines I do 1/8th inch of with per inch of length for the center measurement. Nose and tail actually don’t change that much in measurement. If your changing designs then all this is different.
Sorry to sound ignorant Greg, but what do you mean by “proportional?”
What I’ve done in the past is divide the new by the old e.g. 98"(8’2")/80"(6’8") = 1.225, so if the 6’8" has 2.5" tail rocker the 8’2" would have 3" - does this sound right? Seems OK.
Take the old one, divide by total inches in length, the multiply buy the total inches of length in the new one. example: 7 foot old one = 84 inches. 5 inches of nose rocker divided by 84 = .0595238. New one is 8 foot which equals 96 inches. take the .0595238 and multiply times 96 equals 5.71 inches of nose rocker. This is real easy to do on a calculator. Do this with all pertinent numbers and you have the basis for the scale.
Hi Taylor -
That would be direct proportioning and it works to a point. In extreme enlargements of an existing design, I.E. 7’ to 10’ for example, it results in some extreme (but maybe correct) numbers.
If I understand your concept of a specified rocker angle measure from a known position (i.e. 30% up from tail), you may be on to something with that.
Hey Greg - Works out the same 96/84=1.1428571, 1.143x5(inch nose rocker)=5.715 (ooo - it went up a 100th which would round it up a 10th… Ha. So, it looks like I’ve been doing it right.
But, what about the idea that less rocker = more speed, and maybe one could stretch out the curve of the rocker between certain points? It may not have been clear, but I lay the rocker and foil out on a piece of clear cedar about 1"x8"x “X” inches in the length, and I was pondering a set amount of rocker/“lift” from the “bottom line,” at the 25% from tail point to center line.
John - I find it has been working well for me… and, par for the course, I’m thinking about trying some different stuff later, but I hate to mess w/success. I find it kind of like the scaling thing… a relative proportion.
I cut out my own eps blanks so I work with rocker templates a lot. I recently made an 11’ board and wanted to make a 12’ 6" to be porportionally longer but not taller. On a sunny day I took my 11’ template and placed it over the 12’6" piece of wood that was to be the the new longer stringer material. I tipped the 11’ template up on one end until it cast a shadow 12’ 6" on the new piece. with the stringer proped up I then traced edge of the shadow with a pen.
I have used the same basic idea to reduce board lengths. No math required. I also have a jig (thermo-nuclear rocker tracing machine) set to accurately draw the rocker template from an existing board by tracing the shadow the board cast while turned sidewise on edge to the sun.