What are the floating fences made of that confine spilled oil to the hull vicinity?

The correct answer is linked, buoyant pillows, often referred to as booms. These are specially designed floats that are deployed in water to contain oil spills or other pollutants. The buoyancy helps to keep the boom on the surface of the water, while the linked design allows for flexibility in maneuvering around the spill and adapting to various water conditions. This configuration ensures that the contained oil or spill remains within a controlled area, making it easier to collect and remove, thus aiding in environmental protection efforts.

Other materials like chains, plastic sheets, or metal barriers may serve different purposes in environmental management or construction but do not possess the necessary characteristics for effective use in oil spill containment. Chains lack buoyancy and cannot confine spills on the surface, while plastic sheets may not provide the required stability or flexibility. Metal barriers could be used for other tasks but are typically not adaptable to the dynamic environment of a water surface like buoyant pillows are, which maintain their position despite water movement.