The gods of the sea are wildly different in various mythological traditions. But just as I like my personal spiritual practice to have a broad, comparative-religions kind of base, I like my mythological invocations to have a comparative-mythologies base.
So this is to Ægir and his daughters, and to Manannán, and to all the Sirens. I am the shaman/wizard of my people, and we must pass to the other side of your waters. With my voice and the voices of all my people, I adjure you: permit us to pass your waters unharmed (if not unchanged), and take us not to the after-world.