CREATE TABLE table_name_9 (tonnage VARCHAR(255), ship VARCHAR(255), builder VARCHAR(255), original_operator VARCHAR(255))
What is the Tonnage that has builder AG Vulcan, and the original operator NDL, and the ship, Prinzess Irene?
    
SQL: SELECT tonnage FROM table_name_9 WHERE builder = "ag vulcan" AND original_operator = "ndl" AND ship = "prinzess irene"