Is it permissible for a traveler who spends three months working on a naval vessel and then returns to his country for one month to combine and shorten prayers? And is it better not to combine and shorten prayers in order to perform the supererogatory and regular sunnah prayers?

If the sailing distance of the ship reaches 83 kilometers or more, it is permissible for the passengers to avail themselves of all travel concessions: shortening prayers (qasr), combining prayers (jam'), and breaking the fast (fitr).

Regarding preference, the preponderant view is that a traveler has the choice between shortening and combining prayers, but shortening is better because it was the guidance (Hadi) of the Prophet, peace and blessings be upon him, when traveling. Some scholars have even gone so far as to say that completing the prayer (itmam) is not valid for a traveler.

As for supererogatory prayers (Nawafil), it is permissible for the traveler to pray as many of them as he wishes; there is no contradiction between shortening the obligatory prayer and performing supererogatory and regular (rawatib) prayers while traveling.