It's very common in Latin to use both a compound verb and a preposition (particularly the same preposition already in the compound) whereas in English this seems redundant.
In this example, you still have to use "ad" with "litus" and can't simply put it in the accusative or some other case because it isn't the direct object of the verb. You could just use "...ad litus lata esse...", but Latin prefers the other construction, which emphasizes the motion implicit in the verb (carrying in a particular direction) rather than just the result of the carrying (to the shore).
It isn't always necessary to try to translate both uses of the preposition; just note that they're there and that the author is doing you a favor and reinforcing the relationship between the verb and the noun.
IPHIGENIE: Kann uns zum Vaterland die Fremde werden?
ARKAS: Und dir ist fremd das Vaterland geworden.
IPHIGENIE: Das ist's, warum mein blutend Herz nicht heilt.
(Goethe, Iphigenie auf Tauris)