33 CFR § 401.16 - Propeller direction alarms.
Every vessel of 1600 gross registered tons or integrated tug and barge or articulated tug and barge unit of combined 1600 gross registered tons or more shall be equipped with -
(a) Propeller direction and shaft r.p.m. indicators located in the wheelhouse and the engine room; and
(b) Visible and audible wrong-way propeller direction alarms, with a time delay of not greater than 8 seconds, located in the wheelhouse and the engineer room, unless the vessel is fitted with a device which renders it impossible to operate engines against orders from the bridge telegraph.