MARITIME – DEAD RECKONING & COATAL NAVIGATION CALCULATOR
Cog Sog Calc
A precise tool.
What is the Cog Sog Calc & How does it work?
Dead reckoning estimates a vessel’s future position by projecting its current heading and speed through the water. The heading is measured clockwise from true north and the speed through water (STW) is the vessel’s propulsion speed unaffected by external forces. When a current is present, its own direction and speed must be added vectorially to the ship’s motion. The resulting vector gives the true course over ground (COG) and speed over ground (SOG), which are the quantities actually observed on a chart. By resolving each vector into east‑west (x) and north‑south (y) components, adding them, and then converting the resultant back to a bearing and magnitude, mariners obtain the COG and SOG needed for accurate navigation and position fixing.
\vec{V}_{\text{COG}} = \vec{V}_{\text{ship}} + \vec{V}_{\text{current}}
\vec{V}_{\text{ship}} = ship’s velocity vector (derived from heading & STW)
\vec{V}_{\text{current}} = current’s velocity vector (derived from current direction & speed)
\vec{V}_{\text{current}} = current’s velocity vector (derived from current direction & speed)
Parameters
Result
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Frequently Asked Questions
What is the difference between STW and SOG?
STW is the vessel’s speed through water, while SOG is the actual speed over the ground, accounting for current.
How do I input the current direction in this calculator?
Enter the current direction as degrees clockwise from true north.
Can this calculator handle multiple current speeds?
No, it calculates with one current speed and direction at a time.
What is dead reckoning in navigation?
Dead reckoning estimates position by projecting the vessel’s heading and speed through water, adjusted for current.
How accurate is this COG and SOG calculation?
Accuracy depends on the precision of input data like heading, speed, and current details.
Can I use this calculator for both ocean and river navigation?
Yes, it can be used for any water body where currents affect vessel movement.
What additional information does the calculator provide besides COG and SOG?
The calculator provides a vector representation of the ship’s motion including current effects.
Results are for informational purposes only and do not constitute professional advice.