The correct answer is C) Short in port turnaround times. Ro-Ro (Roll-on/Roll-off) vessels are designed to efficiently load and unload vehicles by driving them directly on and off the ship. This allows for very short port turnaround times, as vehicles can be loaded and unloaded quickly without the need for extensive cargo handling equipment. In contrast, the other answer choices are not characteristic of Ro-Ro vessels - long port stays are not necessary, passenger tours are not typically offered, and heavy vehicles do require robust securing equipment.