It does take more energy to part water than air... at the same speed. Ships benefit in this regard from going much slower. They also benefit from floating by na

It does take more energy to part water than air... at the same speed. Ships benefit in this regard from going much slower. They also benefit from floating by natural buoyancy rather than by burning fuel. Containers in particular are cost-effective because they are packed and stacked very densely -- a passenger ship would have to be uncomfortably cramped indeed to even approach that efficiency.