(d) Clocks or key stations shall be so arranged throughout the vessel so as to assure complete coverage of all accessible spaces required by paragraph (b) of this section. The number and location of recording stations, the order in which they are visited, and the number undertaken by one patrolman shall be specifically approved. The stations shall be numbered as required by § 78.47-23. Sufficient watchmen shall be available so that each space will be covered at least once in every hour except as follows:

1. (1) On existing vessels not constructed in general agreement with §§ 72.05-5 through 72.05-60, of this subchapter, the supervised patrol shall cover all spaces required by paragraph (b) of this section at least once in every 20 minutes.
2. (2) Public spaces constructed in general agreement with §§ 72.05-5 through 72.05-60, of this subchapter, shall have either an approved fire detecting system installed in such spaces or the supervised patrol shall cover these spaces at least once in every 20 minutes.