(a) If you say "There is a cruise ship", we know that there is at least one cruise ship. We can use an existential quantifier (∃x). The word "but" is a conjunction (∧) between "can only go in the river" and "doesn't go on Hudson".
∃x,(A(x)∧¬B(x))
(b) If you say "No cruise ship", that's the opposite of "All cruise ship" and the word "or" is disjunction (∨). It's the same thing as "Every cruise ship cannot go on big river nor Hudson".
∀x, ¬(A(x)∨B(x))