105.3 Dead Reckoning

Question 1

“Dead Reckoning”

Answer 1

Uses only two factors – direction the boat is steered, and the distance it has travelled

Question 2

DR Direction is…

Answer 2

defined by magnetic rose on chart

Question 3

DR Distance…

Answer 3

is simply the number of miles the boat has run through the water

Question 4

Direction sailed + distance sailed will give you a

Answer 4

DR position

Question 5

What does DR not factor into its calcuation?

Answer 5

currents and leeway

Question 6

To lay out a DR plot (three steps)

Answer 6

1. Draw a course line(s) between desired locations
2. Measure direction of each line using magn rose
3. Measure the distance along each line

Question 7

Notations on a DR plot line would include

Answer 7

Course C095M - written above the line
Speed S6.0 – written below the line
Distance (D=10NM) – written to the right of speed, enclosed in parenthesis

Can estimate time from S and D

Question 8

Tidal currents increase in strength when passing through…

Answer 8

narrow passages (Golden Gate 6 knots tidal current)

Question 9

Current that are open to the sea in non-narrow passages will typcially flow at

Answer 9

about one knot

Question 10

A taffrail log was much like a car’s

Answer 10

odometer – spinning torpedo in the water directly increasing a guage on-board

Question 11

What’s the difference between a knot meter vs. a knot log

Answer 11

Car’s speedometer vs. odometer

Question 12

Most important habit in DR is…

Answer 12

recording the time of any DR position along the way (waypoint, passing something, changing course)(

Question 13

In noting time on a chart customary to use

Answer 13

24 hour clock

Question 14

ETA

Answer 14

Estimated time of arrival (ETD + ETE)

Question 15

ETE

Answer 15

Estimated time en route

Question 16

ETD

Answer 16

Estimated time of departure

Question 17

ETE is always measured in…

Answer 17

Hours and tenths of an hour, not hours and minutes (e.g., .5H equals 30 minutes; .2H equals 12 minutes

Question 18

“Yawing” is the….

Answer 18

… normal and unavoidable back and forth from a desired course, but ideally evens out in non-rough seas or wind

Question 19

Factors affecting accuracy of DR (besides current and leeway)

Answer 19

yawing; inaccurate log readings; speed variations

Question 20

What is the rule of thumb of accuracy of a DR plot?

Answer 20

Accuracy within 10% of the Distance RUN

Question 21

Why is it called “Dead Reckoning”

Answer 21

It was originally “Deduced Reckoning” (deduced from direction and distance), then abbreviated Ded., hence Dead…

Question 22

Instead of plotting a straight course to a destination, for a safety valve, select a direction ____, then look or turn ____

Answer 22

5 to 10% UPWIND/WINDWARD of the target; downwind to find intended location

Question 23

A DR safety valve route is useful (three situations)

Answer 23

navigating through fog
navigating at night
approaching an unknown coast

Question 24

What’s different about using DR in heavy weather or heading upwind

Answer 24

Have to create the DR plot lines AS YOU TRAVEL, recording the tacks made to either sail up wind or steer the boat into heavy water.

Question 25

When using DR, at the very start do two things:

Answer 25

1. Set the log to zero or note current reading (e.g., the start trip odometer reading)
2. Note the exact time of departure from starting point

Question 26

When DR upwind, sail as ____ ______ as possible, and note the average ______ at that point, then ___ that heading as the first DR _____. When needed, tack the boat, noting the _____ run on prior course and noting ____ ____ on the chart. Rinse and repeat.

Answer 26

close-hauled; heading; plot; course; distance; “tacking point”

Question 27

Three cautions on using DR: 2 wind, 1 water

Answer 27

1. No allowance for leeway (4 to 8 degrees on sailboat) (wind)
2. Works well when no currents (water)
3. Winds can shift (wind)

Question 28

A useful thing to do is __-___ DR lines on most frequently used charts

Answer 28

pre-plot

Question 29

Be certain a DR plot line does not cross…

Answer 29

dangerous or restricted areas

Question 30

Helpful to plot DR lines from ____ to ____, when possible

Answer 30

buoy to buoy

Question 31

Particularly in fog, you should double check your boat compass with

Answer 31

a second and even third compass

Question 32

If boat has a knot meter, record the ____ ____ on the chart near the plot line

Answer 32

average speed

Question 33

Plot position as a pre-set time _____

Answer 33

interval; set timer to do next recording

Question 34

For nighttime navigation, plot the circle showing the likely distance from a ____ ____ ____ as the radius of the circle

Answer 34

known light source

Question 35

If off course, when should you plot a new DR course?

Answer 35

If your course to return to your track is more than 10 degees different, then plot a new DR. If it is not so radical or your destination is a long way off, “walk” back to original DR line with 5 to 10 degree correction.