Pirate's treasure chest

Step 2 Pick a length and rip your boards

But... but... you said no measurements! Well, yes, but you have to decide how long your treasure chest should be. I just picked the length that would allow me to waste as little wood as possible - I had old six-foot long cedar boards, so I cut the rot off each end and got two lengths out of each piece. The wood I used was nominally 10 x 1, but it varied wildly in width and thickness. If yours are more consistent, your job will be easier.
Rip your boards at a 10 degree angle using a table saw, as shown in the photo below to give them a trapezoidal cross section. Alternate the angle, and keep the fence setting for all cuts. If you organise things well, you won't waste much wood at all.
How wide do you make each board? Well, some simple circle geometry: you will need 10 boards to bring them around in a semicircle (9 joins between 10 boards, each join 2 x 10 degrees, so 9 x 2 x 10 = 180 degrees). The longest edge of your trapezoid is one eighteenth of a circumference, and the circumference of a circle is related to its diameter by pi (3.14...). So the width of your treasure chest will be 18/pi (about 6) x the length of the longest edge. So, for example, if your long edge is 2", your treasure chest will be a little less than 1' wide.
To make your life easier, your treasure chest should be no more than twice as wide as your widest board. You'll see why in the next step.