Which of the following best defines the word 'vessel'?

The word 'vessel' is best defined as a unit designed for navigation on water. This definition encompasses a wide variety of craft, including ships and boats, that are intended for travel across water bodies. By specifying that the unit is designed for navigation, it emphasizes the operational purpose of the 'vessel' within maritime contexts and aligns with the legal and practical connotations often found in maritime regulations and international conventions such as the COLREGs (International Regulations for Preventing Collisions at Sea).

The other definitions, while they may apply to certain types of vessels, do not capture the full scope of what constitutes a 'vessel.' For example, a vessel does not need to be capable of carrying a load or simply be a floating structure without propulsion. Additionally, the idea of transporting people is too broad, as many vessels may be used for other purposes such as cargo transport or research. Therefore, the chosen answer accurately reflects the essential characteristics of what constitutes a vessel according to maritime norms and practices.