On the speed of ships


  • The graph shows annual median speed of ships from 1750 to 2014. It is based on historical location data from 617,754 vessels in the ICOADS dataset.
  • Ship speeds increased by 0.2kn/decade up to 1880. This reflects incremental improvements in sailing ship technology, which reached a peak with Sovereign of the Seas (1852, capable of 22kn).
  • The impact of new technologies such as steam paddle ships (SS Sirius, 1837), steel hulls and screw propellors (RMS Oceanic, 1871) is not evident until the late 1800s. Then, between 1881 and 1905, median speed of ships increased at an astonishing rate ~ 3kn/decade, a near step change compared to the past. The ocean liner SS City of Paris (1889) had a cruising speed of 20kn.
  • From 1906 to 2014, speeds increased at a modest 0.3kn/decade on average, comparable to the rate during the sail ship era.
  • A striking feature of the graph is that the median speed of ships is much more variable in the modern era compared to 18th and 19th centuries. Political and economic factors, rather than technology, became dominant driving forces e.g. oil supply and financial crises. A dramatic example is the sharp decline in speed of ships at the end of 2008 following the collapse of the Lehman Brothers.

R code

Ship trajectories from ICOADS  were stored in a dataframe ships with ~100 million rows.

Rendered by QuickLaTeX.com

Median speeds were calculated using dplyr


ships <- arrange(ships,ID,time)
ships <- ships %>% group_by(ID) %>% mutate(dx = distGeo(cbind(lag(LON),lag(LAT)),cbind(LON,LAT))/1000,dt = as.numeric(difftime(time,lag(time),units="hours")))
shipsV <- shipsdx/ships$dt
ships <- filter(ships, dx !=0 & dt <= 48) #data within consecutive days only
ships <- arrange(testA,ID,time)
shipspeeds <- ships %>% group_by(ID,year) %>% summarise(distance = sum(dx,na.rm=T),speed = median(V,na.rm=T))

The speed of a vessel was calculated whenever it’s location coordinates were available within consecutive days in ICOADS dataset.Periods of zero speed (ship docked or at anchor) were omitted. Buoy and drifter data were excluded.   Insufficient data was available for the years 1864-87.


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