Historical Methods of Positioning at Sea

Abstract

In the previous chapter, geodesy and modern geodetic techniques were reviewed in some detail. Obviously, in establishing a claim to an extension of the continental shelf, countries will, where possible, use the best and most modern techniques available. But in many cases, it will be necessary to use all existing data, including historical data. But the quality of all bathymetry and other data will be influenced by the accuracy with which the vessel collecting it was geographically positioned. Therefore, in reviewing data from charts and maps, particularly those of a historic nature, it is necessary to have a knowledge of the positioning methods used and hence the likely positional accuracy. This chapter reviews the development of the science and technology of navigating at sea and hence the positional accuracy possible. It also traces the development of the technology over the last 200 years, from the introduction of the sextant and chronometer to modern differential techniques using satellite observations. Against this background, it traces the continually improving ability to position vessels accurately at sea and out of sight of land. The bathymetry of most maps and charts available today was collected over a lengthy period, sometimes extending back beyond the turn of the century. This certainly applies to the General Bathymetric Chart of the Oceans (GEBCO) and to most small-scale nautical charts. Accordingly, the data may be of variable quality, as the technology both of measuring the depths and of geographically positioning the data has undergone significant improvements. Few bathymetric charts have been compiled purely from one set of homogeneous and recent data. In evaluating the quality and reliability of the bathymetry and its consequent use for developing offshore boundaries, it is important that the historical development of offshore positioning technology and marine navigation and their limitations with respect to accuracy be understood in order that the quality of the data used to compile the maps and charts can be properly assessed. Until the development of electronic positioning systems during World War II, the positioning of vessels out of sight of land was carried out primarily by observations of celestial bodies and dead reckoning between observations.