piloting and anchoring

04/11/23

Lesson 13: Precise Piloting and Anchoring

• AGENDA:– Ship’s Handling Characteristics– Advance, Transfer and Turn Bearings– Precision Anchoring

• Applicable reading: Hobbs pp. 234-241.

Lesson 13: Precise Piloting and Anchoring

Ship’s Handling Characteristics

• Advance - the distance gained in the original direction until a ship steadies on its final course.

• Transfer - the distance gained at a right angles to the direction of the original course until the

ship steadies on on its final course.

• Turning Circle - the path followed by a ship’s pivot point when executing a 360° turn.

• Tactical Diameter - the transfer involved in the execution of a single turn of 180°.

• Final Diameter - the diameter of the turning circle that a ship would scribe when turning 360°

Final Course

Transfer

End ofTurn

Start ofTurn

Ori

gin

al C

ours

e

Ad

van

ce

Advance & Transfer

E

B

A

F

D

C

Tactical Diameter

Final Diameter

OriginalCourse000

Wheel Over

Tactical Diameter, Final Diameter, and Turning Circle

Example:

Speed: 15 ktsStandard Rudder Angle

Angle of Turn Advance Transfer 15o 180 18 30o 230 30 45o 270 60 60o 310 110

Calculate Advance and Transfer for a 50o turn.

Example cont.

Advance = 270 + 5/15 * (310-270) = 283 yards

Transfer = 60 + 5/15 * (110-60) = 77 yards

Now, let’s look at how to plot this.

Use of Advance/TransferDuring Piloting

• STEP #1 - Calculate advance/transfer from tactical data folder.

• STEP #2 - Plot “transfer” line perpendicular to original course.

• STEP #3 - Plot “advance” by parallel to original course.

• STEP #4 - Draw the turning point.

• STEP #5 - Select a NavAid for a Turn Bearing (TB)/

50

A

TR

N

100 0 100 200 300

Scale in Yards

TR

- 0

00

TR - 05

0

Advance and Transfer TableAngle of Turn Advance Transfer

15 180 1830 230 3045 270 6060 310 110 75 330 170

For a 50 degree turn:

Advance = 283 yds Transfer = 77 yds

77

A

100 0 100 200 300

B

TR

Scale in Yards

NT

R -

000

TR - 05

0

A

100 0 100 200 300

B

TR 90

283

CD Scale in Yards

N

77

TR

- 0

00

TR - 05

0

Turn Bearings

Turn Bearings - In order to plot the position at which the ship must put the rudder over (to turn onto a planned track), you must select a suitable Navaid as a turn bearing.

• Select a Navaid closest to the beam

A

100 0 100 200 300

B

TR

TB 270

90

283

CD Scale in Yards

N

Select a suitable NAVAID as a turn bearing.77

TR

- 0

00

TR - 05

0

Danger Bearings - Are drawn on the chart, displaced from the shoal water by a distance that will keep the ship in safe water even when the pelorus is on the danger bearing.

- The displaced distance will be the equivalent of the distance from the pelorus to either the bow or the stern, whichever is greater.

Danger Bearings

Light

9

9

9 9

9 99

9 95 5

5

5

13

6

pa

FL 6s 58ft 9M

Tank

Long

Point

2021

212121

2121

21

23 23 23 2323 23

1515 15

1717

1717

19

1919 19

12

13

13

13 13

12

12

12

1212 12

20

20

2020

2020

NMT 070

Danger Bearings / Ranges

NLT 200 yds

LightFL 6s 58ft 9M

Tank

NLT 090

Danger Bearings

Trackof the Bridge

Conclusion

• Describe the means by which a ship’s position can be accurately and continuously assessed by visual observation.

• Regular fixes and the use of DR is still required in order to confirm the visual assessment of the navigator.

• The key to successful precise navigation is comprehensive preparation prior to the passage.

Anchoring Stages

• 4 stages of Anchoring:

1. Selection2. Plotting3. Execution4. Post Anchoring

Selection: Determining a Suitable Anchorage

Suitable criteria:• Low winds• Low current• Sufficient and Suitable Navaids• Free of Hazards - Draw the swing circle• Bottom: sand, mud, not rocks• Sufficient Water Depth

Sources of Information

• Chart

• Publications, to include:– Coast Pilots

– Sailing Directions

– Fleet Guides (ports most frequented by USN ships)

• Word-of-mouth

• Pass down files

Plotting Terms

• Approach Track - Final leg that the ship must follow to arrive at the center of the anchorage.

• Head bearing - the final heading of the ship prior to anchoring

• Range circle - arcs plotted along the approach track to indicated the distance from the anchorage. (100 –1000, 1200, 1500, 2000 yds)

• Letting-go bearing- the bearing to a Navaid to that indicates when the anchor should be let go

• Letting-go circle - centered at the center of the berth with a radius of equal to distance from the hawsepipe to the pelorus.

16

16

16

16

16

1616

16

20

20

20

14

14

14

14

14

14 14

12

12

12

10

10

10

10

8

8

8

8

4

4

4

4

4

6

6

6

2

2

2

Mast

Piles

PepeReefUncov.

1 m

HobbsRks

10

Dredged 10 ft 1996R2

G1

R12Fl R 2.5s

G C 3

R N 4

Kentmore marina

Pepe PtFl 6s 54ft 7M

R14Fl R 5s

Red

Hobbs Lt Fl 2s 70ft 15M

1616

2020

14

20

20

Anchorage Plot

HB 040

LGB 140

100

200

300

400

Execution

• Approach slowly• when you reach the letting-go bearing=>

“Let go the anchor !”• immediately shoot a fix.• If done correctly, anchor is within 50 yds

of center of anchorage• Ship is now backed to set the anchor

Post Anchoring

• Anchor scope: 5 - 7 times the depth of the water

• Now, Navigator shoots another fix and notes the direction the anchor is tending => Determine final anchor position

• Draw the SWING CIRCLE.

• If no obstructions exist w/in => OK

• Draw the DRAG CIRCLE.

Post Anchoring Terms

Swing Circle• purpose: to ensure the anchorage is

hazard free

• centered at the position of the anchor

• Radius = (Length of ship) +

(Length of anchor chain)

Post Anchoring Terms (cont)

Drag Circle• purpose: to ensure the anchor is not

dragging• centered at the position of the anchor• Radius =

(Distance from Hawsepipe to Pelorus) +

(Length of anchor chain)

Drag / Swing Circle

Swing Circle

Drag Circle

300 yards

130

yds

Anchorage PlotN

100 200 300 400 500 600 700 800 900 1000

1200

1500

TR 064

TR

004

HB

004

LGB 096Stack

TR

Tank

TB 305

Plotting a Precision Anchorage

Preparation (Pre-Sail):Step 1 - Predict the effects of wind and current along the approach track.

Step 2 - Identify a prominent navaid to use as a head bearing and plot the approach track.

Step 3 - Measure and plot the radius of the letting-go circle over the center of the anchorage


Preparation (Pre-Sail):Step 4 - Scribe and label the range arcs on the

chart.

Step 5 - Select a suitable navaid to use as a Letting-go bearing, and plot the LGB on the

chart.


At Anchor (Post-Sail):Step 1 - As the anchor is “Let go”, take a fix noting the ship’s heading.

Step 2 - Once the fix is plotted, the anchor position is plotted (measured from the fix in the direction of the ship’s head at a distance equal to the distance between the hawespipe and the pelorus.


At Anchor (Post-Sail):

Step 3 - Plot the swing and drag circles around the anchor’s actual position.

Post-anchoring Considerations

• Veer out sufficient anchor chain (scope)

• Cover the chart with acetate over the swing and drag circles

• Select the navaids to use to fix the ship’s position while at anchor

• Set the “Anchor watch”

Homework

• Do the following:

Chapter 14:

#1ab, 2a, 3, 4, 5, 6, 8, 11, 12, 15, 16

piloting and anchoring

Documents