How many vessels are named aqua jewel?
CREATE TABLE "ro_ro_passenger_ships" (
  "ship_name" text,
  "year" real,
  "length" text,
  "width" text,
  "passengers" real,
  "vessels" real,
  "speed" real
);
SELECT COUNT("vessels") FROM "ro_ro_passenger_ships" WHERE "ship_name"='aqua jewel';