Rolex introduced a watch for Regatta racing a few years ago, the Yachtmaster 2. But long before Rolex came on the market with a watch for sailing, Heuer introduced the the first Generation Solunar in 1940s and came onto the market with a second Generation model in the 1970s.
Actually, the first version was introduced in 1949 and the second version was introduced in 1976. The watch here is the latter version.
This watch is reference 279.603. While you may wonder how the Name “solunar” came about, it consists basically of “solar” and “lunar” . Something that makes very good sense considering this is a tide watch and the tides depend on the sun and moon.
This watch carries an ETA 2790-1 movement, a rare automatic movement which was only produced for about 4 years from 1976 to 1980.
For further detailed reading on this timepiece, I recommend These two sites: onthedash and calibre11.