Why do ships need ballast tanks?

Answer 1

They need a certain amount of weight to keep them at a stable height in the water (for propellor effectiveness or to permit them to pass through shallow waters or canals). When they have unloaded a heavy cargo they need some added weight (usually water) held in tanks to give them enough weight.

In old days they used to pick up "low value" cargo at some ports for more weight. Some of that junky cargo turned out to be valued artifacts recognized for its value when it was off loaded.

Answer 2

A ballast tank is a compartment within a boat or ship, that holds water. A vessel may have a single ballast tank near its center or multiple ballast tanks typically on either side. A large vessel typically will have several ballast tanks including double bottom tanks, wing tanks as well as forepeak and aftpeak tanks. Adding ballast to a vessel lowers its center of gravity, and increases the draft of the vessel. Increase draft may be required for proper propeller immersion.

Answer 3

To keep them from becoming unstable and tipping over in rough water. The ballast tanks can be emptied as a ship takes on cargo.

Answer 4

becuse if the weight was off set the ship would be offset so you would fill one of them to counter the weight, it would sit right

Answer 5

To balance them.