The Centers for Disease Control and Prevention (CDC) issued a Federal order, Requirement for Persons to Wear Masks while on Conveyances and at Transportation Hubs, 29JAN2021 (the Order) requiring all persons traveling on all commercial vessels to wear a mask. 

The CDC recently updated their website noting that the following category of mariner is exempt from wearing a mask: “Non-passenger-carrying commercial vessels operated by a team of mariners who all live on the vessel and are the only people on the vessel are also permitted to use this exemption.” 

A mask will still be required when the vessel receives persons who are not a part of the team of mariners that live on the vessel. 

Conveyance operators must continue to require all persons onboard to wear masks when boarding, disembarking, and for the duration of travel, unless they are located in outdoor areas of the conveyance (if such outdoor areas exist on the conveyance). 
Operators of transportation hubs must require all persons to wear a mask when entering or while indoors on the premises of a transportation hub. 
The Order requires conveyance operators and transportation hub operators to take steps to reduce the spread of COVID-19. 
The full MSIB is HERE with the full details regarding mask requirements.