Aboard The Aegre, long before GPS and digital charts on a screen, we plotted our position on large paper charts. That’s all fine on a conventional yacht with a chart table where charts can be left spread out. But we were on The Aegre and there was no room for such a luxury. Instead when plotting our position at sea I would sit on the floor of the cockpit, my feet a little lower in the cabin and balance a piece of plywood, half the size of a chart on my knees. Clipped to it would be the chart in use folded in half, with our last position marked in pencil. This would be marked as DR (dead reckoning, ie based on compass course and speed since the last position), EP (estimated position, DR position adjusted for leeway, currents, tide etc) or OBS (observed ie based on some observation such as land, sun, stars, even RDF (radio direction finding).
Then having consulted the Logbook we kept hourly of our course sailed, estimated or recorded distance, wind strength and direction etc and so on, I’d use a Perspex Harries Course and Bearing Indicator to draw in our course, a pair of dividers to measure off the distance along the course line, and then in pencil mark in our new position, labelling it appropriately as DR, EP or Obs.
After confirming our continuing course, I’d stow my ‘chart table’ up just beneath the deck to starboard where it was held dry and out of the way by shock cord. This whole arrangement for plotting our position at sea worked well.
You can find out more about the Harries Course and Bearing Indicator, a novel instrument that I found invaluable, in The Journal of Navigation, Volume 9, Issue 1, January 1956, pp. 65
See also a page on this website about our navigation charts, also our hand bearing compass and how we measured accurate time for our astro navigation.
