Is a Nebula a fourth-rate warship?

Is the Nebula class a science-fiction equivalent of an age-of-sail fourth rate?

Fourth rate is rejected, but the alternatives depend on whether the question means a Star Wars Nebula, a Nebulon or Star Trek's Nebula.

The question's use of Nebula leaves the intended fictional vessel uncertain. One interpretation is the New Republic's Nebula-class Star Destroyer, while another is Star Trek's Nebula class; Nebulon is also raised as a possible intended name. A fourth-rate comparison is rejected, with higher ratings proposed instead. The reasoning considers whether the ship belongs in a battle line and whether it is built in numbers. The precise rating remains disputed because the speakers do not begin with the same ship in mind.