The engine on a large tug has as much or more power than than many of the cargo ships they are helping into port.
As to why are ships now rated in KW rather than HP. Now days most ships are electric driven. Before most ships were direct drive. And the diesel and turbo electric drive ships had a seperate main buss that powered the main motors. Nowthe ship has one main buss supplying both main engines and hotel load. I would think with looking at electrical load the operator would think in terms of KW rather than Hp. thats my 2 cents.