> The width of the boat doesn't matter too much, surprisingly. It's mostly the length. Well.. The length and the speed determine the Froude number the ship is

> The width of the boat doesn't matter too much, surprisingly. It's mostly the length. Well.. The length and the speed determine the Froude number the ship is operating at, and yes, the length to a large extent determines the achievable top speed. However the beam, prismatic coefficient ("fineness" of the hull shape) and a host of other factors do definitely affect the total resistance quite a lot. Ships designed for high speeds, like warships, tend to have large length/beam ratios and low prismatic coefficients. > From the waterline length you can guess how fast a ship is, regardless of the displacement. So are you saying the Seawise Giant was considerably faster than the Nimitz, considering it had a waterline length of ~450m (!!) vs. a "mere" 317m for the carrier? ;) But yes, I'm quite sure Nimitz doing 45 knots is unrealistic. I'm also quite sure that given the hull shape and size, and engine power, are known, that potential adversaries who have a naval engineer or two on the payroll have a decent idea of what the actual top speed is.