Do you know what dead reckoning is and how to use it? DR is used to calculate a boat’s position along an actual or proposed course line, using the time underway and the speed of the vessel. With GPS on so many boats, people don’t seem to bother much with dead reckoning arithmetic these days, because the GPS can easily calculate time, speed, and distance while navigating toward a waypoint. Dead reckoning is used to plan a trip and to keep track of your progress independently of the boat’s instruments.
Use DR calculations to double check your boat’s position visually and on the chart. Use DR calculations to determine when you should be able to see a particular aid to navigation or landmark based on your boat’s speed and present position. Can you answer the following DR questions? (1) What speed must I maintain to go 45 miles in the six hours before it gets dark? Speed = distance divided by time. (2) The top speed of my boat is about 12 knots; how far can I go in 10 hours? Distance = speed x time. (3) My boat’s average speed is 8 knots; how long will it take me to travel 130 miles? Time = distance divided by speed.
If these little problems are easy for you, it will be a snap to keep a DR plot on the chart or in a log, so you have a backup to your electronics. For the arithmetically-challenged you can buy an inexpensive flat, plastic device called a nautical slide rule, to do the calculations visually. Weems and Plath product #105 is one model. No batteries needed and no formulas to remember!
Use DR calculations to double check your boat’s position visually and on the chart. Use DR calculations to determine when you should be able to see a particular aid to navigation or landmark based on your boat’s speed and present position. Can you answer the following DR questions? (1) What speed must I maintain to go 45 miles in the six hours before it gets dark? Speed = distance divided by time. (2) The top speed of my boat is about 12 knots; how far can I go in 10 hours? Distance = speed x time. (3) My boat’s average speed is 8 knots; how long will it take me to travel 130 miles? Time = distance divided by speed.
If these little problems are easy for you, it will be a snap to keep a DR plot on the chart or in a log, so you have a backup to your electronics. For the arithmetically-challenged you can buy an inexpensive flat, plastic device called a nautical slide rule, to do the calculations visually. Weems and Plath product #105 is one model. No batteries needed and no formulas to remember!
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