"Article 110 of UNCLOS, for example, authorizes warships to conduct right of visit boardings on non-sovereign immune foreign vessels (meaning vessels other than warships or those on other government service) without prior flag State consent, if reasonable grounds exist to suspect that the ship is engaged in certain activities.
One qualifying activity is statelessness, meaning the vessel is not registered/flagged with any State. In these circumstances, warship personnel are authorized to board the ship and conduct a limited inquiry/search to determine whether there is any evidence of registration, such as papers or statements from the ship’s master, that identify a State of registration. If evidence is found, the warship will typically follow a standardized diplomatic process to contact the State of claimed registry to verify the claim. If the State denies the registration claim, the vessel is deemed stateless.
International law also deems vessels as stateless if no claim/no evidence of registration is found during the right of visit boarding or if conflicting evidence is found (i.e., visible signs it is registered in State A but claimed to be registered in State B). Once a vessel is deemed stateless, the “jurisdictional impediments” of exclusive flag State jurisdiction are removed (since there is no flag State)."
