We studied on the following elements of the tides in the Seto Inland Sea.
(I) Meteorological tides observed at four tidal stations (Uno, Takamatsu, Matsuyama and Kure) during the recent five years, 1952-1956. (Appendix Table 1.)
(2) The profiles of the tidal level along the east-westward section of the Sea in different seasons. Osaka, Kobe, Akashi, Takamatsu, Imabari, Hashihama, Mitsuhama and Dannoura were selected as the standard stations for the calculation of the sea level.
(3) Harmonic and non-harmonic constants for the tidal stations located in the Sea.
(4) The time difference and the ratio of the range of tide for the tidal stations in the
I. Meteorological tides at the four stations were computed numerically with the following formula:
Δh = Ht - (Ht-25 + Ht+25) / 2
Δh : Height of the meteorological tide.
Ht : Observed height of tide at the time when the meteorological tide Δh occurred.
Ht-25, Ht+25 : Observed heights of tide 25 hours before and after H, was observed, respectively.
II. Simultaneous heights of tide at the 15 base stations (which are distributed between Osaka and Dannoura over a distance of about 260 nautical miles (Text-fig. I)) are shown in Text-figs. 2-1 to 2-8 for different seasons of the year. From these figures we can see the sectional configuration of the sea level in various seasons, and are enabled to predict the districts where local slope currents will occur.
III. By taking advantage of the tidal currents, one can greatly reduce the time of navigation in traversing the Seto Inland Sea from the east to the west (or in the reverse direction). For example, as is shown in Text-figs. 3-1 to 3-3, a ship with a self-propelling speed of 6 knots and cruising from Osaka to Moji (about 260 nautical miles) can save about 7 hours by making the best use of tidal currents, as compared with the same ship navigating against tidal currents.
IV. The latest values of harmonic constants for 142 stations are summarized in Appendix Table 2. Non-harmonic constants for these stations were calculated from the latest data of tidal observations and are summarized in the following charts:
1. Mean high water interval (Text-fig. 4-1)
2. Diurnal inequality (Text-fig. 4-2)
3. Mean tidal range (Text-fig. 4-3)
4. Spring range (Text-fig. 4-4)
5. Neap range (Text-fig. 4-5)
6. Spring rise (Text-fig. 4-6)
7. Neap rise (Text-fig. 4-7)
V. In Appendix Table 3 we have shown the new time differences and ratios of the range of tide to be applied to the results of tidal observations at the 138 stations located in the Seto Inland Sea and Tosa Bay. In computing these values, we selected as standard stations those 20 stations whose tidal elements had been observed and published in the tide tables by the Meteorological Agency or by the Maritime Safety Agency.