The timeship is a sphere, 1.5 Km in diameter. It is a shell of iron shot. Iron has a density of 7.58 g/cm3. The volume of a sphere is 4/3 𝛑 r3. The volume of the timeship is 4./3. * math.pi * r**3 or 1.413717e+10 m3. If the shell of iron is 3 m thick, the the volume of the inner surface is 1.405251e+10 m3. The difference is 8.465347e+07 m3. The mass of 8.5E+07 m3 of iron is 6.42E+14 g, 6.42E+11 Kg, or 6.42E+08 metric tonnes.
The volume of water is a shell that goes from 1497 m to 200 m. The volume of water is 1.402E+10 m3. A cubic meter of water weighs 1000 Kg. So the water weighs 1.402E+13 Kg.