Speed over groud vs speed over water

This provides the difference between speed over ground and speed through water and its application

1. SPEED OVER GROUD VS SPEED THROUGH WATER By: Gian Gabriel P. Ibo BSMT student

2. Is the speed of the vessel relative to the surface of the earth SPEED OVER GROUND (SOG) 15 knots speed 2knots current 13 NM covered in an hour SPEED OVER GROUND: 13 kts

3. Is the speed of the vessel relative to the water SPEED THROUGH WATER(SW) 15 knots speed 2knots current 13 NM covered in an hour SPEED THROUGH WATER: 15 kts

4. OTHER EXAMPLES: 17 NM covered in an hour 15 knots speed 2knots current SPEED THROUGH WATER: 15 kts SPEED OVER GROUND: 17 kts

5. I s it possible to have zero STW while you have SOG? YES!!! 7 knots current Vessel is dead On water 0 knots Speed over Ground: 7 knots Speed through Water: 0 knots This is possible when a ship is drifting and there is a current allowing the vessel To move 7 knots

6. I s it possible to have zero SOG while you have STW? YES!!! 7 knots current 7 knots Speed over Ground: 0 knots Speed through Water: 7 knots This is possible when a ship has a speed the is the same with the opposing current Opposing current

7. Speed over Ground Speed through water APPLICATION Doppler Log (Ground Tracking mode) Used in Navigation Electro Magnetic Log Doppler Log (Water Tracking mode) Used in Collision avoidance