What is high density solid ballast and why is it needed?

Ballast is the extra weight added to a ship to ensure it has stability and the safety of the vessel and its crew is not compromised when it has no cargo – without it, the ship could become unstable and unresponsive in adverse weather conditions.

Prior to the 1880s, ships used solid ballast materials such as rocks and sand, which was labour intensive and time-consuming as it had to be removed by hand out of cargo holds before new cargo could be loaded.