Your numbers are off. You converted 1 cubic foot to 1 lb. It is around 65 lb.
Ship can't weigh more than it displaces. Roughly 35'X120'X1000'.
Thus you went way under the actual weight by x65.
Hmmm, I wrote this: "...a column of water only 8 feet high, 1 foot wide and 1 foot deep weighs about 500 pounds." I believe this to be correct, since 1 cubic foot of water weighs about 62.5 pounds (just imagine stacking 8 of those on top of each other). I used this 8 ft by 1 ft by 1 ft column in my subsequent calculation.