Practice Cruise Underway - Global Navigation

In addition to the materials used to complete

In addition to the materials used to complete

Part I of this Practice Cruise, you will need

Part I of this Practice Cruise, you will need

:

•

the Excerpts from the 

Nautical Almanac

, contained in

Appendix B of your manual, for all the daily data and

altitude corrections to complete the sight reductions;

•

a copy of any recent edition of the 

Nautical Almanac

for the “Increments & Corrections” tables, the 

NASR

tables, and 

Table A4 Altitude Corrections Tables –

Additional 

Corrections

;

•

blank copies of the 

Meridian Transit Form 

included in

Appendix D of your manual and on 

the USPS

Navigation website;

•

blank copies of the Deck Log included at the end of

chapter 9 in the Student Manual; and

•

Chart N.O. 974, 

Sight Reduction 

forms and 

CLS

lotting sheets, included with your course 

materials.

It’s finally time to leave on your planned offshore cruise

from the Strait of Juan de Fuca, to Honolulu, HI. During

the shakedown cruise, you created a deviation table for

the steering compass, which is contained at the end of

the Practice Cruise; use this deviation table for the

cruise exercises.

As the navigator, you plan to review your Navigator’s

notebook regularly and update it as needed. You’ll use

the GPS as your primary means of positioning, and will

use celestial positioning techniques throughout the

voyage to maintain your skill in taking sights, in the

event your electronics fail and you need to rely solely on

traditional methods for positioning.

As navigator, you also plan to maintain a written Deck

Log and a DR plot using the practices you learned in

both the 

Junior Navigation 

and 

Navigation 

courses,

since you understand the importance of a backup log

and plot in the event of electronics failure. You plan to

manually plot and log waypoints, weather conditions,

etc. every four hours or so, unless circumstances dictate

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You’ve brought with you an adequate supply of the 900

series plotting sheets to cover all the 

latitudes of this

voyage.

For celestial observations note the following:

Height of eye: 10.0 ft

Index error: 0° 1.5' (off the arc)

Watch error: f 0-10 seconds

Watch Time: Using ZT

You and the crew have finished all preparations

for the voyage to Hawaii. The date is 

June 25,

20XX. 

You download a NOAA weather report; it

predicts good weather for the day. The captain

indicates all’s ready to leave the dock at Port

Angeles and travel through the Strait of Juan de

Fuca; you anticipate you’ll arrive at the point of

departure from Cape Flattery, 

WP1

, 

by early

morning.

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Port Angeles is a very busy port, even this early

in the morning; you turn on the AIS (which is

integrated into 

OpenCPN

) to get a view of the

commercial traffic around your boat. You see

many AIS targets on the screen, and maintain a

course through the harbor and the Straits to stay

clear of the commercial vessels.

The GPS is connected to 

OpenCPN 

and you

confirm several of the GPS positions using the

navigation aids in the Strait. All electronics seem

to be functioning properly.

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.

0700

0700

. You reach 

. You reach 

WP1 

WP1 

and take departure,

and take departure,

logging this event and setting the knotmeter log

logging this event and setting the knotmeter log

to zero. The variation in this area is 17° E. The

to zero. The variation in this area is 17° E. The

weather is calm with clear skies

weather is calm with clear skies

.

As you review the 

As you review the 

VPP2 

VPP2 

“Weather Conditions

“Weather Conditions

Report” for Leg 1

Report” for Leg 1

, 

, 

you notice that the current is

you notice that the current is

forecast to have a set of 140° and a drift of 0.4

forecast to have a set of 140° and a drift of 0.4

knots. This will result in a drift angle of about two

knots. This will result in a drift angle of about two

degrees. You plan to set course using this drift

degrees. You plan to set course using this drift

angle and thus the course to steer will be 214°T.

angle and thus the course to steer will be 214°T.

a. 

From your 

OpenCPN 

route, what is the true

course for Leg l

?

Since you’re near-shore and have the paper charts of

this area, you start your DR plot on these charts

simulated for this Practice Cruise)

.

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201°C

1330

. You plan to use celestial techniques

frequently during this voyage, to hone your skills

in sight-taking. Using your sight planning tools,

you find you can get a 2-body fix using the sun

and moon this afternoon. You check and confirm

the sextant error and height of eye (HE) are as

you noted in your Navigator’s notebook. Skies

continue clear, and seas are still four feet, so you

don’t anticipate any problems getting good sights

this afternoon.

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1400

. Your DR position is L 47°32.4’N, Lo 125° 37.0’W.

Winds are northwest at five knots and the knotmeter log

reads 0062.3. At WT 14-00-16, you observe the moon

UL at a sextant reading of 14°14.9'. At WT 14-14-12 you

observe the sun LL with an hs of 57° 21.2'. Reduce both

bodies using the 

NASR 

method (70° F temperature and

barometric pressure 30.10 inches), and plot the resulting

2-body fix on a 

CLS 

plotting sheet. (Don’t forget to

advance the AP of the moon sight)

What is the cut of the azimuths of these two

What is the cut of the azimuths of these two

bodies? Is it adequate for a 2-body fix?

bodies? Is it adequate for a 2-body fix?

Answer

 :

The 

The 

cut is 56°, which is adequate for a

cut is 56°, which is adequate for a

2-body fix since the smaller angle between the

2-body fix since the smaller angle between the

two LOPs must be greater than 45°, which it is

two LOPs must be greater than 45°, which it is

.

Record the coordinates of the resultant 2-

body fix:

At 1414 the GPs indicates a position of L 47° 27.8’N, Lo

125° 38.1’W. How far off is your 1414 Fix from your

1414 GPS position?

Solution: 

See CLS Form, Q 9-4d. Measure distance from the

1414 GPS position to the 1414 celestial fix with dividers

.

•

You know that this distance is primarily due to error in sight-

taking, but are satisfied that your 1414 celestial fix and the

1414 GPS fix positions are fairly close (if your answer was a

few nautical miles).

0

,

8

M

2000

2000

. GPS position is L 46° 42.9'N, Lo

. GPS position is L 46° 42.9'N, Lo

126°19.7'W. Knotmeter log reads 0115.7. Winds

126°19.7'W. Knotmeter log reads 0115.7. Winds

from the west at three knots, seas two feet.

from the west at three knots, seas two feet.

Report to the captain

Report to the captain

.

.

You download a weather report for tomorrow.

You download a weather report for tomorrow.

Prediction is still for good weather, with seas of

Prediction is still for good weather, with seas of

five feet or less and northwest winds 6-12 knots.

five feet or less and northwest winds 6-12 knots.

No fronts seem to be moving 

No fronts seem to be moving 

into your area

into your area

.

You determine that by tomorrow morning, you will be

well offshore and no longer have paper charts to

maintain your DR plot. Throughout the day, you’ve

checked the GPS positions logged in 

OpenCPN 

with

your DR plot and they’ve compared well

.

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appropriate

.

You turn the watch over to the relief navigator, sign off

on the log for the night and go 

off duty.

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26 june 20XX

0545 

0545 

You come back on duty early in the

You come back on duty early in the

morning. As you check the position and deck log,

morning. As you check the position and deck log,

you note that the vessel is about to move into a

you note that the vessel is about to move into a

different time zone

different time zone

.

0556

.

 Crossed over into the new time zone.

 Crossed over into the new time zone.

GPS position L 45°25.7’N, Lo 127° 30.0’W.

GPS position L 45°25.7’N, Lo 127° 30.0’W.

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5

16⁰ E

1017. 

1017. 

You arrive at 

You arrive at 

WP2 

WP2 

and change course to

and change course to

your Leg 2 heading. Knotmeter log reads 0251.7.

your Leg 2 heading. Knotmeter log reads 0251.7.

Your DR position is L 44°55.3'N, Lo 128°10.1'W.

Your DR position is L 44°55.3'N, Lo 128°10.1'W.

Winds are still out of the northwest but have

Winds are still out of the northwest but have

increased to about 10 kn, seas remain at 4 ft

increased to about 10 kn, seas remain at 4 ft

.

From your 

From your 

OpenCPN 

OpenCPN 

route, what is the true

route, what is the true

c

c

ourse for Leg 2

ourse for Leg 2

?

201°V

Plot and log this course change

.

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What is the resultant Compass Course for Leg 2

What is the resultant Compass Course for Leg 2

?

You want to confirm the vessel’s position later in

You want to confirm the vessel’s position later in

the day by developing a running fix using a

the day by developing a running fix using a

meridian transit of the sun and a late afternoon

meridian transit of the sun and a late afternoon

sun sight. You confirm the sextant error and

sun sight. You confirm the sextant error and

height of eye, in preparation of the meridian

height of eye, in preparation of the meridian

transit sun sight

transit sun sight

.

202°T – 16°Var + 4° deviation = 190°C

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What is the calculated latitude?

1200

.

 GPS position is L 44°27.8'N, Lo

 GPS position is L 44°27.8'N, Lo

128°15.9'W. Knotmeter log reads 0269.4 Winds

128°15.9'W. Knotmeter log reads 0269.4 Winds

are NW at 6 knots, seas are four feet. Report to

are NW at 6 knots, seas are four feet. Report to

the captain

the captain

.

.

No question

1645

.

 GPS position is L 43°43.2'N, Lo

 GPS position is L 43°43.2'N, Lo

128°40.1'W. You prepare to take another sun

128°40.1'W. You prepare to take another sun

sight to establish a running fix with the noon

sight to establish a running fix with the noon

sight. At 16-45-22, the hs of the sun’s upper limb

sight. At 16-45-22, the hs of the sun’s upper limb

is 25°27.0'. The knotmeter log reads 0318.3.

is 25°27.0'. The knotmeter log reads 0318.3.

Reduce this sight using the 

Reduce this sight using the 

Law of Cosines

Law of Cosines

method

method

.

.

What is your 1645 DR position?

What is your 1645 DR position?

Solution: 

Solution: 

This position is determined from the

This position is determined from the

knotmeter log distance at 1645, measured from 

knotmeter log distance at 1645, measured from 

WP2 

WP2 

on

on

the DR course line.

the DR course line.

L 43°42.2’N, Lo 128°41.8’W

Record the results of this sun sight reduction

 :

Observed altitude (Ho) :

Computed altitude (Hc) :

The intercept (a) :

The azimuth :

25°07,6’

25°07,3’

0,3 nm T

279°

Determine the running fix with the 1135 MT

sight you reduced earlier

.

What are the coordinates of the running fix?

L43°43,6’N, Lo128°41,9’W

1800

.

 GPS position is L 43°31.3'N, Lo 128°46.6'W; the

 GPS position is L 43°31.3'N, Lo 128°46.6'W; the

skies are clear with a northwest wind at six knots.

skies are clear with a northwest wind at six knots.

Knotmeter log reads 0331.2. Since the GPS seems to be

Knotmeter log reads 0331.2. Since the GPS seems to be

working quite satisfactorily, you decide that a 3-body fix

working quite satisfactorily, you decide that a 3-body fix

during the evening hours will give you an opportunity to

during the evening hours will give you an opportunity to

not only hone your celestial skills but also to determine

not only hone your celestial skills but also to determine

your “shooting” accuracy

your “shooting” accuracy

.

.

Using the procedure you learned in this course, develop

Using the procedure you learned in this course, develop

a first estimate of the ZT of Civil Twilight. Use the SMG

a first estimate of the ZT of Civil Twilight. Use the SMG

of 10.1kn and a CMG of 201°, as forecast by 

of 10.1kn and a CMG of 201°, as forecast by 

VPP2

VPP2

.

.

What is the first estimate position

?

Use the procedure detailed in Chapter 2. The

step numbers (below) refer to the steps 

described

in Chapter 2, para 59.

L43°08,1’N, Lo128°59,0’W

1.

 From the NA excerpts, extract the LMT of CT

for the tabulated latitude closest to the current

GPS position of L 43°31.3'N, for the given date.

The closest tabulated latitude is 45°N, and for the

date of 26 June, the time of CT at 45°N is 2028

.

2. 

Using this as ZT, extend the intended track,

and measure the coordinates. The time of 2028

is 2 hrs 28 minutes (= 148 min) from the current

time (1800); traveling at a SMG of 10.1kn, the

distance traveled in that time is:

D = 10.1 kn x 148 min / 60 = 24.9 nm

3. 

Measure a distance on the N.O. 974 plotting

sheet that is 24.9 nm from the 1800 GPS

position, in the direction of 201°T, and record

the coordinates.

When will the end of Civil Twilight occur at your

When will the end of Civil Twilight occur at your

projected position

projected position

?

Solution: 

Solution: 

From 10.a, the 1st estimate position

From 10.a, the 1st estimate position

at CT is

at CT is

 :

 :

L43°08,1’N, Lo128°59,0’W

L43°08,1’N, Lo128°59,0’W

Use the procedure detailed in Chapter 2. The

Use the procedure detailed in Chapter 2. The

step numbers (below) refer to the steps

step numbers (below) refer to the steps

described in Chapter 2, Example 2, para 37-41.

described in Chapter 2, Example 2, para 37-41.

ZT1956

1.

 For the date in question (26 June, 20XX), find

the time of evening CT listed that brackets the

latitude of interest

.

T

a

b

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C

T

45°N

2028

40°N

2006

  5°

interval    

    22 minutes int.

2. L43°08,1’N – 40° = 3°08,1’ = 3,135°

3. 

(3,135°/5° interval) X 22 minutes interval =

13,79 minutes, rounded to 14 m

4. 

LMT CT for L40°   

     2006

Correction to L43°08,1’N

   +14  

minutes

LMT CT for

   L43°08,1’N         2020

5. Now, find ZT by correcting for DLo

ZM   = 135°

DLo  = Lo –ZM

 = 128°59,0’W -135°W

 = 6°1,0’E

= 6,017°E, rounded to 6,0°E

6,0⁰ X 4 min./degree = 24 minutes

Since DLo is east, the correction is subtracted :

LMT CT

      2020 

(from step 4, above)

DLo (E) 

 -24

 minutes

Z

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1

9

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6

Using 

Celestial Tools, 

plan a 3-body fix for this

date and time (Note: use 2004 for the year).

Print a copy of the Celestial Tools ‘List Visible

Bodies’ in the ‘Sight Planner’screen, and file it in

your Navigator’s notebook

Which bodies have the best magnitude, azimuth

cut, and reasonable altitude for a 3-body 

fix?

(List a few).

Alioth (Vega or Jupiter)-Arcturus;

Altair – Anteres – (Spica or Moon);

(Alioth or Dubbe)-Vega-(Spica or Moon). 

Any of

these groups would be a reasonable choice

.

Question 10 d

Beginning at approximately 1945, you take the

Beginning at approximately 1945, you take the

following sights

following sights

:

Reduce these sights by the 

Reduce these sights by the 

Law of Cosines

Law of Cosines

method, and plot them on a 

method, and plot them on a 

CLS 

CLS 

sheet to

sheet to

determine the 1955 fix position

determine the 1955 fix position

.

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What is your 1955 DR position

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L43°12,0’N, Lo128°58,6’W

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What is the 1955 fix position

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See CLS Form, IM Q 9-10f

.

L43°13,4’N, Lo128°58,2’W

You note that difference between your celestial fix

and the1955 GPS position, and feel confident that

your shooting accuracy is about one nautical

mile

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You download a weather report for tomorrow.

Prediction is still for good weather, with calm

seas. No fronts seem to be moving into your

area

.

You turn the watch over to the relief navigator for

the night and sign off on the log for the end of

your day on duty

.

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You get to the bridge and check the GPS position,

which is L 42°32.5'N, Lo 129°18.0'W; knotmeter

log reads 0395.6. To get a quick picture of

expected weather and sea conditions when you

divert to Crescent City, you decide to download a

weather GRIB with wind, waves, and pressure

information.

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Insert the downloaded GRIB into 

OpenCPN 

and

print a copy of the area of your route showing the

weather information for your Navigator’s

notebook.

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What is the expected wind direction for this route?

(from your GRIB)

Answer:Your wind 

direction depends

upon the date of working this

Practice Cruise.

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Save this route as “Divert CC”. (If the only charts

currently in 

OpenCPN 

of this area are small scale

charts without the detail you need; copy charts

#18603_1 and #18603_2 from 

NOAA onto your

computer.

Print a copy of the waypoint information for this new

route and place it in your 

Navigator’s notebook.

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

Checking the variation in this area, you note

Checking the variation in this area, you note

that you will be entering an area of 

that you will be entering an area of 

15

15

°

°

variation before you arrive at 

variation before you arrive at 

WP2

WP2

. From your

. From your

OpenCPN route, what is the true heading to

OpenCPN route, what is the true heading to

Crescent City between 

Crescent City between 

WP1 

WP1 

and 

and 

WP2 

WP2 

using

using

15° variation?

15° variation?



Answer : 101⁰ T

What is the resulting compass course for this

What is the resulting compass course for this

leg

leg

?

Answer : 101⁰ T - 15⁰ Var - 3⁰ deviation =

083⁰C

You provide the heading information to the captain for

the revised route, and he executes the change in

course to Crescent City. Plot and log this course

change. The DR position at 0030 is L 42°28.2'N,

Lo 129°22.8'W. You re-start your DR course from the

0030 GPS position using a 1° port drift angle

correction, anticipating a northerly current. Due to this

current, you calculate S = 10.3 kn.

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At an average boat speed of 10.3 knots, what is

the total distance and expected time to complete

this voyage as shown in “Route Manager”?

Answer: Distance 235 nm;

time 22 hours 49 minutes

You update your Navigator notebook and check

a few details in 

OpenCPN 

on this revised route.

Your main concern is encountering unexpected

hazards along the route; you see no problems

indicated on the charts for the offshore part of

this revised route and decide to examine the

details of the approach to Crescent City in the

morning. You turn the watch back over to the

relief and return to your bunk

.

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Zoom in on the Crescent City area; switch to

chart # 18603_1 and study the approach 

into the

port.

What dangers do you see on your route as you

approach Crescent City?

There are lots of rocks to avoid in the area as you

approach the channel into Crescent City

.

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Zoom the area of Crescent City harbor to show

WP3, WP4, and WP5. Print a copy and place it

in your Navigator’s notebook

.

You are now satisfied that the route you created to

Crescent City will assist you in getting into the harbor

safely. You return to your task of monitoring Leg 1 of this

route

.

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