How to Calculate Boat Speed

The prudent mariner knows his overall speed of advance at all times.

While a boat speedometer or a global positioning system (GPS) receiver can tell you how fast you're progressing toward your destination at a given second, when you're under way and making way toward a destination, you may want to calculate your boat's speed between two points on the voyage--your "speed made good"--or how fast you need to go to be at a given point by a given time.

Things You'll Need

• Navigational dividers

Instructions

1. Measure the distance between the two points on the chart where you wish to know the speed made good.

2. Divide that distance by the number of hours required to travel: from the time you left the first point until the time you arrived at the second point.

3. The result is you "speed made good" or speed of advance, for that leg of the voyage, in nautical miles per hour.

References

• National Geospatial-Intelligence Agency: Chapter 8, "The American Practical Navigator"; NGA; 2010