what is the maximum tonnage where date entered service is 25 march 1986 
CREATE TABLE "ships_operated_by_zeeland_steamship_comp" (
  "ships_name" text,
  "date_entered_service" text,
  "date_withdrawn" text,
  "tonnage" real,
  "type_of_ship" text
);
SELECT MAX("tonnage") FROM "ships_operated_by_zeeland_steamship_comp" WHERE "date_entered_service"='25 March 1986';