46 C.F.R. § 121.404 – Radars.

(a) Except as allowed by paragraph (b) of this section, all self-propelled vessels must be fitted with a Federal Communications Commission (FCC) type accepted general marine radar system for surface navigation with a radar screen mounted at the primary operating station.
(b) The following vessels are not required to carry a radar:
1. (1) A ferry that operates on a rivers route within one mile of land; and
2. (2) A vessel operated on a short restricted route, when the cognizant OCMI has determined that a radar is not necessary due to the vessel's route and local weather conditions.
(c) The radar and its installation must be suitable for the intended speed and route of the vessel.