Navigation and Seamanship

3.2.1. Introduction

Speed logs are basic requirement for successful navigation. The navigator must know his vessel speed, which is useful in calculating right time of arrival to the destination and distance travelled by the vessel. The speed is also required to calculate his approximate position at sea. The speed log is a device used to measure the speed of a moving vessel. Generally the unit used for expressing the speed of a vessel is knots (Nautical miles/hour).Logs are used on vessels to record the speed and also the number of nautical miles the vessel has travelled through the water in a given time.

Speed log are generally classified in to two types

i) Conventional logs

ii) Modern logs