CREATE TABLE table_63947 ("Ship" CLOB, "Built" FLOAT, "In service for NAL" CLOB, "Type" CLOB, "Tonnage" CLOB)

The ship SSBergensfjord built before 1973 has what tonnage?
SELECT "Tonnage" FROM table_63947 WHERE "Built" < '1973' AND "Ship" = 'ssbergensfjord'
SELECT "Tonnage" FROM "table_63947" WHERE "Built" < '1973' AND "Ship" = 'ssbergensfjord'