Why is the balance between visual navigation and instruments so important? Let me start with two examples: Close to 20 years ago I made my first voyage supported by a portable pilot unit (PPU). A PPU is in a number of ways comparable to an ECDIS. This particular PPU displays an outline to scale of the ship on the chart, making use of real time kinematics (RTK). It is accurate down to the centimetre, with two antennas and state-of-the-art software, which allow the heading, SOG and RoT to be calculated into decimals or better, and the software provides a very accurate 'prediction'. I enthusiastically made use of the new equipment, and coming up to a turn from 100° to 077°, I took this entirely on PPU, checking the predictor continually. Previously, I had always navigated this turn visually. I never had any problems with this turn; controlled-turn techniques are not really necessary. However, this time, using PPU with predictor, I took the turn far too wide, and I came close to grounding. Later I will explain why this happened.
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