What is "Dikisa"?
Radak: (You crushed.) Dikisa is written with an Aleph in place of a Yud. The same applies to "Ripinu Es Bavel" (Yirmeyah 51:9). First You split the sea for Yisrael, and afterwards You crushed the Egyptians in it, as if they were dead bodies; they had no strength to flee and leave the sea when it was dry land.
What is "Rahav"?
Rashi: It is Egypt. Radak - it says "ha'Machtzeves Rahav" (Yeshayah 51:9), "Azkir Rahav u'Vavel" (above, 87:4). this proves that the previous verse discusses Keri'as Yam Suf.
Why does it say "Pizarta Oyvecha"?
Radak: [Normally,] The sea expels those who drown in it, and scatters them on the shore after days, but not immediately after they drown. With the arm of Your strength, the sea expelled them immediately after they drowned, so Yisrael will see them dead on the shore.
Malbim: You scattered them "bi'Zero'a Uzecha" - by Yourself, without any help from lower beings or their deeds, only with His supreme strength.
