33 CFR §67.25-10

1. (a)The owner of a Class “B” structure shall:
   1. (1)Install a sound signal that has a rated range of at least one-half mile, except that the District Commander may—
      1. (i)Prescribe a greater rated range, not to exceed 2 miles, under the provisions of paragraph (b) of this section; or
      2. (ii)Exempt the structure from the requirements of this paragraph, under the provisions of paragraph (c) of this section;
   2. (2)Operate the sound signal when the visibility in any direction is less than 3 miles, unless the District Commander establishes a greater or lesser distance of visibility, not to exceed 5 miles, under the provisions of paragraph (b) or (c) of this section.
2. (b)The owner of a Class “B” structure shall install a sound signal with a greater rated range or operate it at times of greater visibility than required in paragraph (a) of this section if:
   1. (1)The structure is erected on or adjacent to the edge of a:
      1. (i)Navigable channel;
      2. (ii)Fairway; or
      3. (iii)Line of demarcation; and
   2. (2)The District Commander decides a greater range or operation of the sound signal at times of greater visibility is necessary for the safety of marine commerce.
3. (c)The District Commander may waive or relax the provisions of paragraph (a) of this section, if he or she finds that a structure is:
   1. (1)So close to other structures and so enveloped by the sound signals on other structures that it is not a hazard to navigation; or
   2. (2)So located in a shoal area that it is not a hazard to navigation.