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Sea TimeSea Time

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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.

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Practical Exercises:

Problems 1 through 2

Follow the Student Manual for guidance

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3. On 2 March, a watch reads 22-30-56 at the instant a 2230 time signal is received. On 4 March at the 2230 signal, it reads 22-30-55; and on 6 March, it reads 22-30-54. What is the rate of this watch?

a. 1 second per day slow.b. 0.5 second per day fast.c. 2 seconds per day slow.d. 0.5 second per day slow.

REF: ¶ 6-8

Watch has lost 2 seconds in 4 days, so rate is slow 0.5 second per day.

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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 2- hour intervals at least 6 times.d. commercial radio time announcement at hourly intervals for a full day.

REF: ¶ 7

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5. WWV /WWVH stations broadcast on:

a. 16.25,16.5,16.75, 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 14.670 MHz.

REF: ¶ 12

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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.

REF: ¶ 31

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7. Using a current Almanac, find the zone descriptions for the following places on 15 March:

a. Halifax, Nova Scotiab. Auckland, New Zealandc. Reykjavik, Icelandd. Rangoon, Burma

Ref. Nautical Almanac Standard Time Tables beginning on page 262

List III ZD+4List I ZD-12List II ZD+0ZD -6 hr 30 min

REF: ¶ 25

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8. Zone Description (ZD) is:

a. always positive in east longitude.

b. the longitude of the zone meridian divided by 15° & rounded to a whole number, 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

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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

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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?

Figure 3-13

ZT = 0400

UT is 1900 the previous day

Lo = 135°E

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 1900ZD -9 (rev) ZT 2800 -24ZT 0400

c. The Sun is 75°/(15°/hr) = 5 hr before g, so UT = 2400 - 0500 = 1900 the previous day.

REF: ¶ 36, 37

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11. You take a sextant observation and record the time of the your observation. What ‘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

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12. For each of the following longitudes, find the zone description (ZD).

a. Lo 137° 14.5'W b. Lo 42° 55.5 'E c. Lo 7° 29.2 'W d. Lo 7° 29.2'E

d. Solution: -(7° + (29.2' / 60)) / 15 = 0.49911 ZD = 0

REF: ¶ 39 - 43

ZD = +9ZD = -3ZD = 0ZD = 0

a. Solution: (137° + (14.5' / 60)) / 15 = +9.149ZD = +9

c. Solution: (7° + (29.2' / 60)) / 15 = 0.49911 ZD = 0

b. Solution: -(42° + (55.5' / 60)) / 15 = -2.86 ZD = -3

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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

REF: ¶ 45 - 52

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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=-

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REF: ¶ 54 - 56

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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?

Solution:ZT1 1630 Guayaquil time of planned contact ZD1 +5 Guayaquil ZDUT 2130ZD2 +6 (rev) Vessel time ZD ZT2 1530 Local time of call (same day)

REF: ¶ 59 - 64

Ans: ZT 1530, ship's clock time

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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?

Solution: ZT1 0830 London time of planned contact ZD1 +0 London ZDUT 0830ZD2 +6 (rev) Chicago ZDZT2 0230 Chicago time of call (same day)

REF: ¶ 59 - 64

Ans: ZT 0230, same day, in Chicago

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17. On 24 December, a vessel 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?

Solution:When crossing the IDL in an easterly direction, you are going from east Lo to west Lo, and you will 'lose' a day.

ZT1 2400 24 Dec ZT & date before crossing IDLZD1 -12 ZD before crossingUT 1200 24 DecZD2 -12 (rev) ZD after crossingZT2 0000 24 Dec ZT & date after crossing

ZT3 1200 25 Dec ZT2 -0000 24 Dec ET 12 hr 1 day = 36 hoursREF: ¶ 69 - 72

Ans: 36 hrs will elapse

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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

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19. Find UT and date for the following:      

UT Date23-26-00 11 Mar

03-28-28 13 Mar

05-54-14 23 Aug

01-02-32 31 Mar

Watch Time WE ZD Date

a. 07-27-14 f 1-14 -8 12 Mar    b. 19-27-14 s 1-14 +8 12 Mar    c. 11-52-28 s 1-46 -6 23 Aug    d. 20-02-32 0-00 +5 30 Mar

REF: ¶ 49 - 52

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