In this context, you shouldn’t just take the word soit by itself, but the expression soit… soit, that you can translate as either… or. So in this sentence, we want to say that the ships that he see everyday are either sailing ships or steamboats.

Let’s take another example:

Je vais au marché soit le lundi, soit le mardi.

You can translate it as:

I go to the market either the Monday or the Tuesday.