Buoyancy is basically whether an object floats or not, which is obviously really important to a good boat. But to be more specific, it's the upward forces created by the displaced water. In order to make an object buoyant, you have to make the boat weigh less then the water. In my boat the roles of buoyancy were mostly played in the bottom. I placed holes in the boas to make it less dense and heavy.
Stability is the state of being secure and balanced, that's important to the penny holding challenge. I added in fin so It would even out the weight, I also put a penny slot, in case it did fall over. I made sure that the boas were all the same weight and mass.
This is my boat being tested.
My boat almost met the requirements. It floated really well on its own and held three pennies successfully. Although, When we added waves to the water, the pennies slipped off the edge. My boats buoyancy, when compared to the others, was good. Other boats sunk under the weight of the pennies but my boat stayed firmly above the water. But my stability compared to the other boats was not as good. As soon as the water got rough the pennies fell off while other boats had walls to keep the pennies secure.
The next time I use Tinkercad and print out a boat I would do things a little differently. I would have wanted to make the penny slot a little bigger so the pennies would actually fit. I would add walls at the edges of the boat to keep the pennies from falling out and I would have made the flap bigger at the bottom to make it more stable and to last out the waves.