CREATE TABLE table_77988 ("Date" TEXT, "Ship" TEXT, "Type" TEXT, "Nationality" TEXT, "Tonnage GRT" FLOAT)

what is the tonnage grt of the ship author?
SELECT "Tonnage GRT" FROM table_77988 WHERE "Ship" = 'author'
SELECT "Tonnage GRT" FROM "table_77988" WHERE "Ship" = 'author'