I designed my boat nearly like a box (without top lid), or a tray. I faced a choice of whether I should make the walls higher, or the base larger. And I made it a rectangular prism. I was able to fit the whole box of coins on there. But not the second box. My boat would have carried a lot more coins if the material was stronger. In the end, the walls on 2 longer sides enclosed, bent in the middle and sank. If I am to rebuild the boat, I will make the walls much higher. And I will fix the brims so they are pointing up but diagonally, instead of perpendicular to the base. So when it collapses, there will be less effect. My boat demonstrated an understanding of buoyancy. Because I knew that buoyancy equals to the amount of water the boat displaces, the larger the volume is, the better it floats. And the largest thing you can make with a limited surface area is a sphere. But that’s not testable, so a cube would be the best. I didn’t get to see the winning boat, so I can’t answer the last question.