maritime

  [1] Background The compass, sextant, chronometer, and radar are tools that fix the ships position on a chart, meaning the position is a known place “on the ground”. The speed of a ship is another parameter important to navigation and historically has been achieved by measuring the passage of an object alongside the ship. The principle is that an object thrown overboard stays stationery as the ship moves past it. If we can measure the time it takes for the ship to pass the object, we can measure the speed of the ship. There is an important provision here. It measures distance travelled through the water not “over the ground”. Therefore the effects of water mass movement, tide and wind on the ship are not taken account of. The structure of the log is simple. A quadrant-shaped piece of wood is weighted with lead to hold the quadrant vertical in the water. A bridle is attached to each corner of the quadrant and then to a log line that is wound on a spool. A release line is ...

  [1] Background Technology has been central in the development of new tools for   the ship’s navigator and RADAR, the fourth in this series of articles, is a classic example. However it had one major advantage over the earlier tools, it did not require visibility for the navigator to see and identify objects. It could see in the dark and in dense fog, a major benefit for the navigator. It is also one of   the newer tools in the navigators toolbox having been developed in the late 19 th . century. [2] Radio Detection and Ranging (RADAR) was first used for ship detection in the early part of the 20 th . century. Its ability to detect metal objects by returned radio waves from the object was the basis of the modern marine radar. In the early 1960’s I was a newly qualified third officer responsible for the 8-12 watch on the bridge and had a brand new Radar Observers Certificate. The scenario was one that is stressful for a navigator, to say the least! Friday night i...

  [1] Background Whilst latitude had been known and calculated for centuries the same cannot be said for measuring longitude, that essential east and west component of a ship’s position. The early navigators exploring and discovering new worlds relied on what became known as latitude or parallel sailing. Not knowing their longitude they followed a southerly course, often along a known coastline before sailing a constant latitude east or west to their destination. Christopher Columbus’s first voyage illustrates this method. [2] On his first voyage (the blue line on the map), in 1492, he followed the known voyage to the Canary Islands where he carried out repairs before setting out on a westerly parallel course until he discovered an island in the Bahamas. For his return voyage he went northerly until he reached the latitude of Lisbon when he started his easterly latitude sailing. It is important to remember that navigation was relatively crude in this period and charts covered...