What type of buoy may be used for Special Marks?

Special Marks are utilized in the IALA Maritime Buoyage System to indicate particular areas of interest that do not fall under the standard navigational aids, such as safety measures or navigation channels. These marks can signify various things, such as under-water pipelines or cable routes, and are typically designated with specific color schemes and symbols.

The term "Optional" relating to Special Marks refers to the non-mandatory nature of the information they provide. Unlike mandatory marks that are crucial for safety or navigation compliance, Special Marks serve more of an advisory purpose. As such, their placement and significance can vary depending on local circumstances or needs, reinforcing their classification as "optional." This flexibility allows mariners to be informed about special conditions without the rigorous requirements that pertain to mandatory navigational aids.

Fixed and permanent markings refer to the physical characteristics or durations of a buoy's presence, which do not inherently relate to the status of being special as compared to mandatory or optional aids. Thus, they do not classify the mark under the necessary descriptor of Special Marks.