The Posuk says: ???????????? ????????? ????????? ???????????? ?????????? ?????? ?????????? ???? ??? ?????? ???? ?????????? Why on boats?
Rav Kanievsky answers it says in Medrash Eicha(?”? ??’ ?) That the Jews had a treaty with Egypt’s King Pharaoh the Limp and an enemy attacked the Jews they called on Egypt an the Egyptians were coming to save them. Hashem caused the bodies of the Egyptians who had drowned at the splitting of the sea to surface one asked the other who are these people they answered theses are our ancestors who the Jews drowned and the turned around and left.This is why the Boats are mentioned as this was the Payback for our sins.