The course followed by Titanic was designed to reach New York from Ireland by the most economical route, consistent with safety.
The shortest route would have been by a great circle course, but this has the slight disadvantages of passing through Arctic ice and also across Newfoundland, to which its citizens would have objected.
It was therefore planned to steer a great circle course from Ireland to a point well clear of ice at 42°N, 47° W. From there a rhumb line course of 266°T would be steered for New York.
In practice, a great circle course is steered in a series of rhumb lines, with the course usually being changed at every 10° change of Longitude. This procedure resulted in Titanic heading for her last turning point on a course of 242° T. Her final change of course to 266° T brought her heading back towards the ice field.
As the turning point was approached, efforts would have been made to determine the ship's position as accurately as possible, given the means available. This would have been done by taking a sun sight late in the day, when the sun bore nearly west, and working out a Longitude by Chronometer. This would have given the Longitude to within a mile or so. The estimated Latitude may have been somewhat in error, however, as it was obtained by carrying forward the Noon Latitude obtained nearly six hours earlier. This carrying forward depended on dead reckoning, based on the estimated speed and the course steered and hence was open to errors.
By the time of the collision, Titanic was some 5 miles south of where she would have been, had she been perfectly on course. This is believed to have been due to Captain Smith electing to hold his course for about 30 minutes after passing the turning point and perhaps a small error in Latitude at the turning point.