The TugSafe International Addendum provides guidance for applicability of international conventions on towing vessels required to comply with 46 CFR Subchapter M that operate internationally. This job aid was designed with the assumption that a vessel holding a valid international certificate is equipped in accordance with the same, and the equipment is in serviceable condition. Requirements are based on length, build date and a tonnage measurement system. NVIC 11-93 Change 3 provides Coast Guard guidance on applicability of tonnage measurement systems.