1. Junior Navigation Chapter 3
Sea Time
Homework
Q & A
Junior Navigation
Chapter 3

2. ■Determine watch error and rate. 1
Objectives:
■Determine watch error and rate.
■Obtain an accurate time check by radio time signals.
■Determine zone description from longitude.
■Find the zone description for standard time zones ashore.
■Determine Universal Time (UT) for sights
■Convert zone time (ZT) to Universal Time (UT).
■Convert Universal Time (UT) to zone time (ZT).
■Convert one ZT to a second ZT.
■Allow for travel time or other intervals in zone time conversions.
■Describe the principles of timekeeping at sea.
■Draw a time diagram to visualize longitude, UT, and ZT.

3. Follow the Student Manual for guidance1
Practical Exercises:
Problems 1 through 2
Follow the Student Manual for guidance

4. 3
3. On 2 March, a watch reads at the instant a 2230 time signal is received. On 4 March at the 2230 signal, it reads ; and on 6 March, it reads What is the rate of this watch?
a. 1 second per day slow. b second per day fast. c. 2 seconds per day slow. d second per day slow.
Solution:
2 March 4 March 6 March
Watch Time 22–30–56 22–30–55 22–30–54
Time Signal 22–30–00 22–30–00 22–30–00
fast fast fast
Watch has lost 2 seconds in 4 days, so rate is slow 0.5 second per day.
REF: ¶ 6-8

5. 4. To determine the rate of a timepiece, compare the timepiece to a:
a. radio time signal at 12-hour intervals for 3 days. b. radio time signal at 24-hour intervals for 1 week. c. radio time signal on one day at hour intervals at least 6 times. d. commercial radio time announcement at hourly intervals for a full day.
REF: ¶ 7

6. 5. WWV /WWVH stations broadcast on:
a ,16.5,16.75, and 17.0 MHz.
b. 2.5, 5.0, 10.0, 15.0, and 20.0 MHz.
c. 2.5,5.0, 10.0, 15.0, and 20.0 KHz.
d. 3.30,7.335, and MHz.
REF: ¶ 12

7. 6
6. The effect of Daylight Saving Time on the observer's zone description (ZD) in western longitudes is:
a. to add 1 to its value. b. to subtract 1 from its value. c. negligible. d. not determinable.
Our ZD on the North Olympic Peninsula is +8, expect when we are observing Daylight Saving Time, we set our clocks ahead by one hour (Spring Ahead) and the ZD becomes +7.
REF: ¶ 31

8. 7
7. Using a current Almanac, find the zone descriptions for the following places on 15 March:
a. Halifax, Nova Scotia b. Auckland, New Zealand c. Reykjavik, Iceland d. Rangoon, Burma
List III, ZD+4
List I, ZD-12
List II, ZD 0
ZD -6 hr 30 min
Ref. Nautical Almanac Standard Time Tables beginning on page 262
REF: ¶ 25

9. 8. Zone Description (ZD) is:
a. always positive in east longitude.
b. the longitude of the zone meridian divided by 15°, with a plus or minus sign (depending on if W or E longitude).
c. the difference between Universal time and local time, expressed to the nearest hour.
d. the difference between zone time and local time, expressed to the nearest hour.
REF: ¶ 28

10. 9. ZT 0000 occurs at your zone meridian when:
a. the apparent sun is overhead. b. the apparent sun is on the horizon. c. the mean sun is 180° from the upper branch of the zone meridian.
d. the mean sun is at the upper branch of the zone meridian.
REF: ¶ 34

11. UT 1900 ZD -9 (rev) Figure 3-13 REF: ¶ 36, 3710
10. In the time diagram shown in Figure 3-13 (below): a. What is the observer's longitude? b. What is his ZT? c. What is UT?
Lo = 135°E
ZT = 0400
UT is 1900 the previous day
a. From Time Diagram in Fig. 3-13, Lo is 9 hrs. east of G and Lo = 9 x 15° Lo = 135°E.
b. ZD = 135°E / (15°/hr) = -9
UT ZD -9 (rev)
ZT 2800
-24 hr ZT 0400
Figure 3-13
c. The Sun is 75°/(15°/hr) = 5 hr before g, so UT = = 1900 the previous day.
REF: ¶ 36, 37

12. 11
11. You take a sextant observation and record the time of the your observation. Which ‘time’ do you use to enter the Nautical Almanac?
a. local standard time throughout the year b. local daylight time when applicable; otherwise, local standard time
c. Universal Time (UT) d. Universal Time (UT) adjusted for Daylight Saving Time if applicable
REF: ¶ 38

13. a. Solution: (137° + (14.5' / 60)) / 15 = +9.149 ZD = +912
12. For each of the following longitudes, find the zone description (ZD).
Lo 137° 14.5' W
Lo 42° 55.5' E
Lo 7° 29.2' W
Lo 7° 29.2' E
ZD = +9
ZD = -3
ZD = 0
a. Solution: (137° + (14.5' / 60)) / 15 = ZD = +9
b. Solution: -(42° + (55.5' / 60)) / 15 = ZD = -3
c. Solution: (7° + (29.2' / 60)) / 15 = ZD = 0
d. Solution: -(7° + (29.2' / 60)) / 15 = ZD = 0
REF: ¶

14. 13. For each of the following zone times, find UT.
a. Zone time is 1000 in zone +6
Ans: 1600 UT
b. Zone time is 1800 in zone -6
Ans: 1200 UT
c. Zone time is 1600 in zone +9
Ans: 0100 UT next day
d. Zone time is 2000 in zone -12
Ans: 0800 UT
Solution
a b c d ZT
ZD +6 –6 +9 –12 UT
– day
0100 next day
REF: ¶

15. 14. For each of the following UT, find the corresponding zone time.
a. UT is 1800, Lo is 75°W
Ans: 1300 ZT. ZD=75/15=+5
b. UT is 1800, Lo is 75° E
Ans: 2300 ZT. ZD=75/15=-5
c. UT is 1000, Lo is 135° W
Ans: 0100 ZT. ZD=135/15=+9
d. UT is 1000, Lo is 135° E
Ans: 1900 ZT. ZD=135/15=-9
Solution:
a b c d UT
ZD +5 – –9 (reverse, all) ZT
REF: ¶

16. Ans: ZT 1530, ship's clock time
15. You are fishing in the Galapagos Islands and have arranged to make radio contact daily at 1630 (their time) with Guayaquil, which keeps zone +5 time. You keep zone +6 time aboard. What is the ship's time of the radio contact?
Ans: ZT 1530, ship's clock time
Solution: ZT Guayaquil time of planned contact
ZD Guayaquil ZD UT
ZD2 +6 (rev) Vessel time ZD
ZT Local time of call (same day)
REF: ¶

17. What will the time be in Chicago when you make your call?16
16. You are in Chicago and wish to speak to a business associate in London, England. He can be reached by telephone only at 8:30 A.M., London time.
What will the time be in Chicago when you make your call?
Ans: ZT 0230, same day, in Chicago
Solution:
ZT London time of planned contact
ZD London ZD UT
ZD2 +6 (rev) Chicago ZD ZT Chicago time of call (same day)
REF: ¶

18. 17
17. On 24 December, a vessel at Lo 179° E bound eastward at 10 knots for the Hawaiian Islands expects to cross the International Date Line at midnight (ZT prior to the crossing).
How many hours thereafter will plum pudding be served at noon, Christmas Day?
Ans: 36 hrs will elapse
Solution:
When crossing the IDL in an easterly direction, you are going from east Lo to west Lo, and you will 'lose' a day.
ZT Dec ZT & date before crossing IDL ZD ZD before crossing UT Dec ZD2 -12 (rev) ZD after crossing ZT Dec ZT & date after crossing ZT Dec
ZT Dec
ET hr day = 36 hours
REF: ¶

19. 18. The vessel's log and plot should be kept according to:
a. zone time. b. ship's time. c. Universal Time. d. Daylight Saving Time.
REF: ¶ 78

20. 19. Find UT and date for the following:
Watch Time WE ZD Date
a f Mar    
b s Mar    
c s Aug   
d Mar
UT Date
Mar
Mar
Aug
Mar
REF: ¶

21. Junior Navigation Chapter 3
Sea Time
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Junior Navigation
Chapter 3