The answer will depend on the size of the cube.
That depends on the density of the material in the cube. It would be different if, say, the cube were made of ice, iron, or gold.
Iron is magnetic, lead is not.
The iron boat is an "empty shell" with air filled space inside, reducing its density compared to the iron cube which is iron all the way through.
the weight and the cube
Multiply the volume of the cube by its density.
It depends on the cube's size, not the cube's weight, due to the amount of displacement caused by a larger sized cube than when compared to a smaller sized cube.
The volume of a cube of iron that is 2.50 cm on each side is: 15.63 cm3
The curb weight of the 2013 Nissan Cube is 2789 lbs..
The curb weight of the 2009 Nissan Cube is 2762 lbs..
The curb weight of the 2011 Nissan Cube is 2789 lbs..
The curb weight of the 2010 Nissan Cube is 2768 lbs..
The curb weight of the 2014 Nissan Cube is 2798 lbs..