Container ship and tug boat. The tug boat has very powerful engines and, working with other tug boats (not seen), is used to guide the ship to its mooring place. The ship's own engines wouldn't be able to manoeuvre it quickly enough to avoid an accident. The containers are the large rectangular boxes stacked up on the deck of the ship. They are a uniform size for ease of handling and storage. They can be transported by lorries and trains, and then moved on to the ship. This container system is an efficient means of transporting many and varied types of cargo. Photographed at the Port of Long Beach, California, USA.