Glossary Term
Marine Sanitation Device (MSD)
A Marine Sanitation Device, or MSD, is equipment designed to prevent the discharge of untreated sewage from a vessel. The term is especially tied to United States regulatory usage. The U.S. Coast Guard states that MSD regulations in 33 CFR Part 159 govern the design, construction, and certification of equipment that prevents discharge of untreated sewage from vessels into U.S. waters.
In yacht context, the phrase usually comes up when a yacht trades into U.S. waters, is built to U.S.-facing requirements, or has sewage equipment discussed in U.S. regulatory language. Internationally, the broader compliance frame is still MARPOL Annex IV, which covers sewage discharge and the equipment and systems used to control it. So an owner or manager may hear both expressions around the same yacht, depending on flag, operating area, and documentation set.
For the technical team, the practical question is less about the label and more about the function: is sewage retained, treated, monitored, and discharged only within the rules that apply to the yacht’s operating area. That usually brings the MSD into the same decision space as machinery and equipment selection, sanitary pipe routing, holding capacity, and shore interface planning.