This is not right. Once you release the ball that force which sent it into the air has ended, the forces acting on the ball now are gravity and air resistance. Both these forces are in opposite direction to the direction the ball is moving. Metal is heavier than water so a ship made of metal must sink. What is important is not the weight but the density of the material.
Density is the mass divided by the volume.
Provided the object has a lower density than this then it will float. It is possible to float things on water which would otherwise sink. A very special property of water is its surface tension. It is not easy to explain surface tension without resorting to chemistry but water molecules are attracted to one another because of chemical bonds. This acts as a sort of glue holding the molecules together.