Stranded cruiseliner passengers have spent another day at sea as their broken down ship is hauled back to shore by two tugboats. The Norwegian Star's propulsion system malfunctioned on Friday morning after leaving port, forcing it to bob without direction 30km off the coast of Melbourne. Operating company Norwegian Cruise Line said guests would be back in Melbourne by Saturday afternoon, but the process had been delayed. "It all comes down to the towing process, it's not a perfect science," NCL spokeswoman Anne Wild told AAP. "They have to wait until the water conditions are correct for it to come through." The boat had been tugged into Port Philip Bay by Saturday afternoon with guest expected to return to Melbourne by Sunday morning. Ms Wild said morale on the ship remained "buoyant" and passengers were enjoying the amenities of the luxury cruiseliner. While there has been engine failure, the boat still has power and the facilities are fully functioning.