Marine Navigation Cruise

Akron Power Squadron - Marine Navigation Class

Part  3 - Starts on p 99 (Appendix A)

Finding the answers to the cruise is like solving a puzzle.  You piece together the "clues" and determine your course and position, plotting on the chart.

Part of the challenge of the cruise is knowing where to start. Here is a list of the lat/lon positions of key locations in part 1 of the cruise. Latitude is in degrees N, longitude is degrees W. If you see any errors below, please let me know.

Fl 8s 42 ft 8M beacon on Duttons Island. 41° 44.0' N, 071° 44.2' W
G “7” Fl G 4s 41° 37.4' N, 071° 50.0' W
G C “1” at the entrance to Blackfish Creek 41° 34.6' N, 071° 53.8' W
G C “3” within the Creek. 41° 33.9' N, 071° 54.4' W
G “5” Fl G 4s GONG 41° 38.6' N, 071° 46.4' W
G “3” Q G 41° 39.4' N, 071° 39.4' W

The cruise is found in Appendix A, p 97 of the Student Manual.

The cruise is taken on Bowditch Bay.  For all questions, use a variation of 15 W
HW Questions about Cruise

At the end of Part 2, your vessel is south of Channel Island.  You have just taken a fix at 1316, and your position is L 41° 39.2’ N, Lo 071° 53.5’ W.

9. You plot a course to the Fl 8s 42 ft 8M beacon on Duttons Island. You want to proceed until you reach the 18 ft. sounding line outside Duttons Island. You proceed at a speed of 25 kn.​

​Measure the true course to the beacon, then determine magnetic course.  Label course line with the  magnetic heading.

T = 055°  
V = 015 W
C = 070° M

Plot and label the Course, C 070 M, above the course line, and your speed below the course line, S 25.0.  Speed is to nearest tenth of knot. 

9. a What is your ETA at the 18 ft. sounding line?

You can measure the distance of this leg with your dividers and the latitude scale.  The distance to the 18' sounding line is 7.2 nm.

Determine ETA by calculating how long it will take to travel 7.2 nm.  Use the starting time of your fix, 1316.

 D = 7.2
  60 D = ST
  60 * 7.2 / 25.0 = T
  17.28 min = T
rounding to nearest minute, 17 min.  Add 17 minutes to the time you started the leg.

The ETA becomes

   + 0017

ETA at the 18 ft. sounding line is 1333.

9. b  What will be your DR position at that time?

Measure latitude and longitude with your dividers

L 41° 43.3’ N, Lo 071° 45.6’ W. 

9. c   Along the course to the west end of Duttons Island you note at 1323 a small power boat to your port and you take a relative bearing of 340°. Later at 1325 you note the small boat now has a relative bearing of 025°. Most likely what is your course of action and why?

For question 9c, I plotted the bearing of the vessel at 1323 and 1325.  To do this, I first calculated the 1323 DR, and the 1325 DR.  Then, I drew a bearing line representing the bearing at 1323, and another at 1325.  I used a dashed line for the bearings, since these were not my vessel's course, nor were they bearings used to develop a "fix."    

1323 DR:                  1325 DR:

  1323                       1325
- 1316                     - 1316
   0007 min                0009 min

Distance traveled:

   60 D = ST                              60 D = ST
   D = 25 * 7                              D = 25 * 9
            60                                       60
    D = 2.92 rounds to 2.9         D = 3.75 rounds to 3.8

Since each sighting of the boat is at a relative bearing, we must convert to True bearing before we can plot on our chart.  Then, in order to label each bearing, you must calculate the magnetic bearing.  Remember, you measured your course to the Duttons Island light as 055 True:

TB = RB + TH                          TB = RB + TH
TB = 340° + 055°                     TB = 025° + 055°
TB = 035°                                 TB = 080°

Then, convert to magnetic bearing, and label the two bearings

T = 035°                     T = 080°
V = 015 W                  V = 015 W
M = 050°                    M = 095°

These bearings are plotted with time above the dashed line and the bearing below.

Question 9c asks, "Most likely what is your course of action and why?"  In the Marine Navigation Student Guide, Ch 6, paragraph 42-43 (page 85), the text mentions the use of relative bearings to determine whether you are on a collision course with another vessel.  

If the relative bearing between your vessel and another vessel does not change, you are on a collision course with that vessel.

Since the relative bearing changes, there is no likelihood of collision, so your vessel should maintain its speed and course.  

If you look at the position of the second vessel at both times, it appears that the second vessel has already passed in front of your vessel.

10.  You arrive at the 18 ft. sounding line outside Duttons Island at 1335. Your son shows you how to find your position on the GPS.  At 1335 your position is L 41° 43.4’ N and Lo 071° 44.8’ W.

Plot your GPS position at 1335.  Label this as a fix, "1335 GPS".   

What is the distance between your 1333 DR and your 1335 GPS FIX?  Measure the distance between the DR and the fix with your dividers.

    The distance between the 1333 DR and the 1335 GPS FIX is 0.7 nm

11.  At 1603, you take a GPS Fix.  Your GPS position at 1603 is 41° 43.0’ N and 071° 43.0’ W. 

Plot the 1603 GPS Fix.

You develop a route on the GPS to G “7” Fl G 4s and then to G C “1” at the entrance to Blackfish Creek

Plot the course from the 1603 Fix to G "7".  Measure the True couse, and label the course in magnetic, with speed of 15.0 kts.

T = 223°
V = 015 W
M = 238°

You want to monitor any Cross Track (XTE) error to avoid the rocks near G “5” Fl G 4s GONG. You want to leave a margin of at least 0.4 nm.

As shown in Figure 3 and figure 4 of "Plotting and Labeling Standard," use a dashed line to represent the XTE and label "XTE D 0.4" for a distance of 0.4 nm.  Note in this case you could have set XTE at approximately 1.0 nm before coming close to the rocks.

11. a Before you depart, you want to preserve this location for future reference as a fishing spot. What button on the GPS did your son press to enter the 1603 location? Depending on the GPS model, you would press "MARK"

11. b What is the heading to G “7” Fl G 4s ?  You measured this above:  238 M.

11. c What information should the GPS provide for your navigation after you have entered
the route? What is that information for each leg?

Name of each WP, bearing to next WP, distance to next WP, cumulative
distance, ETE or ETA

12.a   As you approach G “7” Fl G 4s the GPS indicates a distance of 8.1 nm and a bearing of 092° M to the next waypoint in the route. You know the distance should be 3.9 nm and the bearing should be 240° M.  What did you do wrong?

In this case, I plotted the course C 091 M  and distance of 8.1 nm.  I used a dashed line to indicate this was a construction line.  You need to convert to true to plot this line 

T = 077
V = 015 W
M = 092

When you plot this course and distance, you see it is the course and distance to G "3" QG, located at L 41° 39.4' N, Lo 071° 39.4' W.  You have entered the wrong waypoint in your GPS route.

12 b.  What three items of information will the GPS give you when you press “nearest waypoint” on the menu screen as you pass by R “6” Fl R 4s on your starboard beam?

Waypoint name:  BBR6

Waypoint bearing:  328°  (see calculation below)

Assume that you are passing at a SB beam bearing, ie, RB = 090°.  Your course is 238° M.

Your GPS is setup so that it reads magnetic bearings, so your calculnn all be in "magnetic".

MB = RB + MH
MB = 090° + 238°
MB = 328°

Waypoint Distance:  0.7 nm  (measure the distance from your course line to R "6" with your dividers)