This paper sets out to describe some of the ways in which merchant seamen may make useful sketch surveys of anchorages, coastlines or even whole islands, so as to improve the official charts, plans and sailing directions in areas which lack complete surveys by naval surveyors. These areas in fact include hundreds of miles of coastline, and hundreds of square miles of water where the depths are dangerously uncertain. The paper also describes some unorthodox uses of the official charts and, finally, attempts to show the usefulness of these improvements. All the work described has been done in the south-west Pacific, among the islands of Melanesia, where good surveys are few, and the gaps are filled in with scraps of early surveys.