What is the responsibility of vessels under GMDSS?

The correct answer highlights the essential communications functions that every ship must be capable of performing under the Global Maritime Distress and Safety System (GMDSS). GMDSS was developed to enhance maritime safety and ensure a higher level of communication during emergencies. This system mandates that all vessels, regardless of size, be equipped with certain communication devices and systems to facilitate effective distress communication and safety operations.

By stating that every ship must be able to perform those necessary communications functions, the answer emphasizes the obligation of vessels to maintain safety standards, thereby contributing to the safety of both the vessel itself and other vessels in its vicinity. This aspect of GMDSS ensures that ships can send and receive distress signals, relay navigation and safety information, and communicate with search and rescue operations if needed.

The other options present varying conditions and misconceptions about assistance responsibilities under GMDSS. While it's true that vessels over a certain size typically have more extensive requirements, the fundamental principle of GMDSS is that all vessels must be equipped to communicate effectively regarding safety, which is encapsulated in the correct answer.