Ships Before Steam: The Trade-Wind Highways of the Age of Sail in British, Dutch, Spanish and French Logbooks, 1750 to 1850

Ships' logbooks recorded a position and the wind every day, and the CLIWOC project digitised 260,631 such entries from British, Dutch, Spanish and French archives for climate research. I use them as a record of where sailing ships went. Cutting 1,973 logbook records into 6,524 passages of daily positions, I measure the great sailing routes, voyage times and the winds the officers wrote down. Ships between Europe and the South Atlantic crossed 30° N at a median of 18° W outbound and 36° W homebound, the westward loop known as the volta do mar; 66% of homebound crossings of 38° N passed the longitudes of the Azores, against 2% of outbound ones. Dutch ships bound for Java crossed 75° E at a median of 38° S, keeping to the Brouwer route through the roaring forties. The median voyage from home waters to Batavia took 102 days (219 voyages), 176 before 1820 and 101 after. Averaged in 5° squares, the logbook winds point within 45° of a modern reanalysis climatology in 97% of squares where the modern wind is steady. The record is a sample of surviving, mostly naval logbooks, uneven by nation and decade, and I report its coverage alongside every result. Interactive version: https://maps.tristanhotham.com/ships-before-steam/. Data and code: https://github.com/Tristan-Hotham/ships-before-steam. Blog post: https://blog.tristanhotham.com/2026/10/31/ships-before-steam/. Data: CLIWOC v2.1 (García-Herrera et al. 2005, Climatic Change 73, 1 to 12), released by the Universidad Complutense de Madrid and KNMI, via the GeoJSON by Francisco Correoso (github.com/kikocorreoso/cliwoc_vis); openly published research data for which no formal licence was found, credited in full. NCEP/NCAR Reanalysis 1 (public domain). World Bank and IMF Global Shipping Traffic Density (CC BY 4.0). Natural Earth (public domain). This study's text, figures and derived data: CC BY 4.0. Code: MIT.