Lesson 8: Dead Reckoning 4/2/2014
Lesson 7: Dead Reckoning • AGENDA: • Definition of Dead Reckoning • Six Rules of Dead Reckoning • Define/Apply the 3 min & 6 min Rules • Applicable reading: Hobbs pg. 134-138.
Dead Reckoning DR is the process of determining a ship’s approximateposition by applying, from a known position, a vector or a series of consecutive vectors representing the true courses steered and the distance run as determined by the ship’s speed and time,without considering the effects of wind and current.
Dead Reckoning • DR is derived from DEDUCED, or DED, reckoning which was the process by which a vessel’s position was computed trigonometrically in relation to a known point of departure. • This is performed as often as required by the 6 rules of DR • Uses: • Determine present position • Project future positions relative to hazards • Measure the effects of current (winds, seas) • Alter course to account the effects of current
0846 Plot a new Course Line with Every Fix or Running Fix c-075 s-15 0937 R-Fix c-106 s-10
Plot a DR Position Every Hour on the Hour 0900 1000 1100
Plot a DR Position atEvery Course Change 29 20 c-090 C-080 C-125 24
Plot a DR Position atEvery Speed Change 21 27 15 S-10 S-15 S-5
Plot a DR Position for Every Line of Position (LOP) c-195 s-10 Tank 0826 0826
0846 Plot a DR Position for Every Fix or Running Fix 46 37 0937 R-Fix
Speed-Time-Distance Calculations • STD calculations can be made using a nautical slide rule, electronic calculator, set of pre-computed tables, or speed nomogram. D = S x T where: D = distance traveled S = speed in knots T = time in hours
Three Minute Rule • In 3 minutes a vessel travels in yards a distance 100 times its speed in knots. D = S x 100 where: D = distance traveled (yds) S = speed in knots
Six Minute Rule • In 6 minutes a vessel travels in miles a distance equal to its speed in knots divided by 10. D = S / 10 where: D = distance traveled (nm) S = speed in knots
REVIEW • What is Dead Reckoning? • What are the 6 Rules of DR?