33 CFR 83.06: Safe speed (Rule 6).

Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions. In determining a safe speed the following factors shall be among those taken into account:

(a) By all vessels:

(i) The state of visibility;

(ii) The traffic density including concentration of fishing vessels or any other vessels;

(iii) The maneuverability of the vessel with special reference to stopping distance and turning ability in the prevailing conditions;

(iv) At night, the presence of background light such as from shore lights or from back scatter of her own lights;

(v) The state of wind, sea, and current, and the proximity of navigational hazards;

(vi) The draft in relation to the available depth of water.

(b) Additionally, by vessels with operational radar:

(i) The characteristics, efficiency and limitations of the radar equipment;

(ii) Any constraints imposed by the radar range scale in use;

(iii) The effect on radar detection of the sea state, weather, and other sources of interference;

(iv) The possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range;

(v) The number, location, and movement of vessels detected by radar;

(vi) The more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity.