What is the common term for small ropes used on a vessel?

The common term for small ropes used on a vessel is "lines." In nautical terminology, the term "lines" refers to any rope or cord used on a ship, regardless of size. This includes everything from thicker mooring lines to thinner ropes used for various tasks on deck.

While "small stuff" can colloquially refer to smaller ropes, it is not the standard term used in nautical contexts. Additionally, "twines" usually refers to even thinner strands or threads, often used for light-duty applications and not specifically in maritime language. "Straps" typically denote flat pieces of material rather than cords or ropes. In summary, "lines" is the most broadly accepted and utilized term within the maritime community for ropes of any size.