Navigation and Seamanship (1+1)

1.3.1.3. To find out speed and distance

                                                                         

    

Logs

Chip log or ship log was used to determine ship speed in 16^th century. It consists of piece of wood in the shape of a quadrant, weighed with lead at the centre. This log chip was secured to a bridle at each corner. The bridle was connected with log line. Long log line was wound on a free turning reel.

          To determine speed, the log chip was put over board, where it floated vertically due to its ballasting, a considerable length of log line was let out, as the ship moved forward the line was pulled off the red. When the first knotted marker on the line passed off the red timing was started, at the end of a definite period, the line was seized and the number  of knots in the line that had paid out were counted to determine the vessels speed.

Modern logs

            3 types of modern logs are used in general.

i. The pilot static log

ii. The impeller type

iii. Electromagnetic log

            These logs require the use of rod meter projecting through the bottom of the ship in to the water. Rod meter contains sensing device.

RPM

            The engine revolution counters provide a convenient means of determining speed and distance.