Final answer:
When a pushing vessel and a vessel being pushed ahead like a tugboat and barge combine efforts, they are treated as a composite unit, acting as one entity on the water.
Step-by-step explanation:
When a pushing vessel, such as a tugboat, and a vessel being pushed ahead are operating together, they are often considered to be a composite unit. This composite unit behaves like a single entity in terms of navigation and movement on the water. For example, if two tugboats are pushing on a barge, they all move in the direction influenced by the sum of the exerted forces, which can be determined through vector addition. In physics, this is similar to how velocities are added as vectors, such as with a kayak moving on a river that experiences combined velocities: one due to its own movement relative to the water, and one due to the current's movement relative to the riverbank.
For navigational and regulatory purposes, these composite units must adhere to specific rules and conventions designed for such scenarios. In many cases, especially when it comes to larger vessels such as barges being moved in commercial or industrial settings, accurately depicting the forces is essential for safety and operational efficiency. The composite unit is often treated like a single vessel in terms of how it's steered, controlled, and how it interacts with other traffic on the water.