Weight won't matter much (you typically only accelerate it once, and the additional drag is small), it is just that the surface area is so small relative to what's needed that it just doesn't move the needle.

Drag is huge for boats, especially in seas and oceans that have tides and currents. Far more than a car... that also have to continuously burn oil to keep their speed, even on freeways.

From the current top comment on this thread:

> It's made out of aluminum instead of steel. The resulting weight savings make it a bit more efficient. That's something this shipping yard specializes in.

According to that person, weight does indeed matter.