I heard it was common practice to give seamen going to Israel a new passport as any Israeli stamp in your passport would make it impossible to get a visa for Saudi Arabia and several other Arab countries.
To obtain a Saudi entry visa you used to have to get a letter from a priest or minister confirming that you were a Christian (ie (presumeably) not Jewish). I recall joining a ship in Jeddah and the 4th Engineer didn't arrive, much to the annoyance of the incumbent 4th. He finally arrived about 6 weeks later in Aqaba - he had failed to get a visa for Saudi because he sent his application in with a note saying: "I am a hermaphrodite!".
Not a bad way to getr extra leave.