49 C.F.R. § 39.27
(a) As a PVO, you may take action to deny transportation or restrict services to a passenger with a disability if necessitated by legitimate safety requirements. Safety requirements must be based on actual risks and not on mere speculation, stereotypes, or generalizations about individuals with disabilities.
Example 1 to paragraph 39.27(a):You may take such action in order to comply with Coast Guard safety regulations.
Example 2 to paragraph 39.27(a):You may take such action if accommodating a large or heavy wheelchair would, together with its occupant, create weight and balance problem that could affect adversely the seaworthiness of the vessel or impede emergency egress from the vessel.
Example 3 to paragraph 39.27(a):You could restrict access to a lifeboat for a mobility device that would limit access to the lifeboat for other passengers.