I want to start calculating the volume of the boards I make. Can you do this by hand? i was thinking for a short board you could start with the tail, the middle, and the nose, using a trapezoid, a rectange, and a triangle. The trapezoid and triangle would go from the tip of the board to the +./- 1 ft mark on each end, and the average thickness could be found using calipers. Simple math could get you the rest of the way.
Leme know what you think, and if you have any other ways of finding volume.
If you know calculus you’ll be familiar with taking an infinite amount of estimations to get the actual answer, aka an integral. Especially on lower volume boards, counting a trapazoid might be the difference between several liters over the entire board, and when you’re talking 28 liters and it’s plus or minus 3 liters that’s over 10% error.
If you put the board in a fluid of known density and measured the weight necessary to totally sink it, wouldn’t that lead you to the volume? Seems sort of silly, but it’d work.
BoardCad or as drzoidberg stated, sink it, that’ll get you the most accurate displacement, but you’d need a graduated bathtub to do so
Using integral calculus would be a nightmare, depending on how accurate you want to be, due to the constantly changing angles, you’d have to take a lot of measurements.
I’m with your original idea, get some calipers and measure width, and length at a series of points and turn them into shapes that can be easily calculated i.e. rectangles and right triangles, to figure out surface area (i.e. sq inches)
To get the thickness, for the same section, do the same thing on the rocker profile, break it up into rectangles and right triangles again. If it’s a rectangle, multiply area by the thickness. If it’s a triangle, multiply area by 1/2 the thickness. Sum up all the sections. The more sections, the more accurate it is, but with diminishing returns for your effort - that’s the theory that makes integral calc work. You get to avoid making about 100 extra measurments by taking that shortcut at the expense of some precision.
I have been thinking about the tank thing for a while and came out with this idea: build a rectangular tank in which the whole board can be immersed. Figure out the exact volume of the tank (inner length X inner width X inner depth). Fill it with water until water reaches the very edge at the top. Then immerse the board. Obviously, water will overflow. Take the board out, measure what’s left in height of water and re-calculate the volume of water left. The difference between the first and the second measure will give you the board’s volume. Another easier way would be to have an exit for the overflow leading to a can on a scale that would immediately give the weight of displaced water and thus the volume.
I think I remember an old Surfer Mag ad (G & S?) using this tank but with a scale written in it. Does it ring a bell in someone’s memory? Bill T? Sammy?
