Question: Why does a boat carry more mass when the surface area is larger?
Thanks for giving your age Yeena, because, I'm afraid, it is a bit complicated. It has to do with displacement, buoyancy and a chap called Archimedes.
OK, some things float, but not all. If you don't sink to the bottom, then that means you are getting an upthrust that keeeps you up. An upthrust is a force from the water that acts upwards and stops you from sinking.
When an object goes into the water, then it will displace so much water and the it's the amount of water displaced that decides how much upthrust it gets. The amount of upthrust is equal to the weight of the water (displaced). And the weight of water displaced is proportional to the volume of water displaced.
So now we get to your ship.
You ship will be so deep into the water. The keel of the ship will be so many feet below the water-line. (This is called the ship's draught.) But the volume of water displaced by the ship will not only depend upon the depth of the keel, but also on the cross-sectional area of the ship at the water-line.
So, for ships with the same draught, then the bigger the cross-sectional area, the more water will be dislaced and so the greater the up thrust, so the ship can carry more tonnage (more mass).
That's a simplification. The hull of a ship is curved and that's makes it more complicated.
HTH
Fermat
