What makes maritime records so useful is that standard methods for record keeping were used, improving as ship technologies improved, he says.
When reviewing a ship log, Mock says he first looks at wind scale, which is measured from 0 – 12. Six or above indicated a tropical storm or a “gale,” the term commonly used until the advent of “hurricane” in the late 19th century. Winds in the 10 – 12 range hint of something exciting, a possible hurricane, Mock says.
Mock then looks at the barometric pressure, wind direction and weather descriptors for more clues. Of the 12 basic weather descriptors used, the most common include Q for squalls, C for cloudy, R for rain, L for lightning, U for ugly, G for gloomy and B for blue sky.
U.S. ships adapted the British system of meticulous record keeping. While British logs go back to the early 1700s, U.S. logs only extend back to the early 1800s. The earliest useful U.S. log book for hurricane data is from the War of 1812, says Mock.
Vivid notes were commonly written in the margins of the logs by the weather columns. An excellent example of this is a log kept by the U.S.S. Para that detailed a hurricane near South Carolina on Sept. 16, 1863. Etched in the margins was a description of heavy rains in the 4 p.m. hour that developed to “heavy squalls from the Eastward increased to a gale” by 5 p.m. Entries at 5:10 and 5:20 p.m. described the dragging of anchors, the laboring of the vessel, the battening of the hatches and the securing of everything on board.
Mock says U.S. ship logs were particularly thorough during the Civil War because of the Union naval blockade. In contrast, the Confederate Navy has few records.
“I discovered about 50 percent of the hurricanes in the ship logs,” he says. “I made changes to the strength of hurricanes that we knew about based on what I found in the logs. Many of the ones in New England were Nor’easters. I also discovered a new hurricane in 1714 and a hint of another one hitting Georgetown in 1729. Unfortunately, many Georgetown records were destroyed during the Civil War, which would provide more information.”