Sink
a big heavy steel ship floats on water because the volume is mostly air. trust me its true.
Yes, a cork will often float on the surface of water, depending on the cork's density. But a marble will sink in water because of its weight. It will not float on the surface.
Provided the boats and the ships displace their weight in water without the water coming inboard, they will float and not sink. A boat made of wood is likely to float even when full of water because wood tends to float. It is all to do with displacement and freeboard.
Ships float in fresh water too. Only a little deeper, since fresh water is less dense than salt water.
Sink
yes
Your question is too broad. How big are the marbles and how big is the bag?
very big
Because the boat has a special shape that makes it less dense than water.
a big heavy steel ship floats on water because the volume is mostly air. trust me its true.
Cruise ships float with help from density and a principal called buoyancy.because of greater surface area.
Put them in water.
The devils marbles look think two big red marbles and they are red as well!
The ships are built in drydocks which can be flooded to float the ships out.
the size of marbles
No, ships float on the sea, aircraft fly in the air. NO similarity.