Allah says,
(Or do you feel secure), `you who turn away from Us after acknowledging Our Oneness at sea once you are back upon dry land,'
(that He will not send you back) to sea a second time
(and send against you a Qasif) which will destroy your masts and sink your vessels. Ibn `Abbas and others said, "Al-Qasif is the wind of the sea which destroys vessels and sinks them."
(and drown you because of your disbelief) means because of your rejection and turning away from Allah.
(Then you will not find any avenger therein against Us.) Ibn `Abbas said that this means a helper. Mujahid said, "A helper who will avenge you," i.e., take revenge on your behalf. Qatadah said it means, "We are not afraid that anyone will pursue Us with anything of that nature (i.e., vengeance)."