30 current sailing
TRANSCRIPT
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Navigation
NAU 102
Lesson 30
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Current Sailing
The horizontal movement of the sea surface.
Current
Expanded Definition
All factors that cause a ship to depart from its intended course and DR.
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Current Sailing
Factors
•Ocean Current•Tidal Current•Wind-driven Current •Wind•Seas
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Current Sailing
Factors
•Compass Errors•Steering Errors•Engine Calibration Errors •Speed Log Errors•Fouled Bottom•Unusual Trim
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Current Sailing
Current
The combined effect on a vessel of all the factors.
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Current Sailing
The art of selecting courses and speeds to compensate for the effects of current in
order to arrive at your desired destination.
Current Sailing
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Current Sailing
•Track (TR) – the intended direction of travel.
Important Terms
•Set – the direction towards which a current is flowing.
Speed of Advance (SOA) – the speed intended to be made good.
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Current Sailing
•Drift – the speed of a current.
Important Terms
•Speed Made Good (SMG) – speed along the Course Made Good.
•Course Made Good (CMG) – the resultant direction from a point of departure to a
subsequent position.
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Current Triangle
Course & Speed
CMG & SMG
Set &
Dri
ft
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Current Triangle
Course & Speed
CMG & SMG
Set &
Dri
ft
If you know any 2 sides, you can solve for the 3rd side.
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Current Triangle
Course & Speed
CMG & SMG Set &
Dri
ft
If you know the Course & SpeedAnd the Set & Drift
You can get the CMG & SMG
Estimated Position
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Current Triangle
Course & Speed
CMG & SMG Set &
Dri
ft
If you know the Course & Speed
You can solve for the Set & Drift
And the CMG & SMG
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Current Triangle
Course & Speed
CMG & SMG Set &
Dri
ft
You can solve for the Course & Speed
And the Set & Drift
If you know the CMG & SMG
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Current Triangles
Can be solved using:
Charts
Universal Plotting Sheets
Radar Plotting Sheets
Maneuvering Boards
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Solving for Set & Drift
Problem Type #1 - Determining an Unknown Current
Given two positions (fixes) and your course and speed, solve for the current.At 0919 your position is LAT 37°00.0'N,
LONG 75°30.0'W. You are on course 270°T at 8.7 knots. At 1000 your position is LAT
36°59.5'N, LONG 75°37.0'W. What was the current?
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Solving for Set & Drift
Step 1: Plot the 1st position.
Step 2: DR to the time of the 2nd position.
At 0919 your position is LAT 37°00.0'N, LONG 75°30.0'W. You are on course 270°T at 8.7 knots. At 1000 your position is LAT 36°59.5'N, LONG 75°37.0'W.
What was the current?
0919C – 270
S – 8.7
1000
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Solving for Set & Drift
Step 3: Plot the 2nd position.
At 0919 your position is LAT 37°00.0'N, LONG 75°30.0'W. You are on course 270°T at 8.7 knots. At 1000 your position is LAT 36°59.5'N, LONG 75°37.0'W.
What was the current?
0919C – 270
S – 8.7
1000
1000
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Solving for Set & Drift
Step 4: Complete the Triangle.
At 0919 your position is LAT 37°00.0'N, LONG 75°30.0'W. You are on course 270°T at 8.7 knots. At 1000 your position is LAT 36°59.5'N, LONG 75°37.0'W.
What was the current?
0919C – 270
S – 8.7
1000
1000CMG/SMGSet &
Drift
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Solving for Set & Drift
Direction From DR to Fix = Set
At 0919 your position is LAT 37°00.0'N, LONG 75°30.0'W. You are on course 270°T at 8.7 knots. At 1000 your position is LAT 36°59.5'N, LONG 75°37.0'W.
What was the current?
1000
1000
CMG/SMG
Set = 137° T
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Solving for Set & Drift
Distance DR to Fix Converted to Speed = Drift
At 0919 your position is LAT 37°00.0'N, LONG 75°30.0'W. You are on course 270°T at 8.7 knots. At 1000 your position is LAT 36°59.5'N, LONG 75°37.0'W.
What was the current?
1000
1000
CMG/SMGDistance = 0.6 nm
0.6 nm41 min
X 60 min/hrDrift = = 0.9 kts
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CMG/SMG
You are underway on course 315°T at 10 knots. The current is 090°T at 2.3 knots. What is the course & speed being made
good?
Problem Type #2Given the Course & Speed and a known
current, determine the CMG & SMG (Estimated Position).
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CMG/SMG
Step 1: Plot the 1st position.
(If no position given, start in the center of compass rose or radar plotting sheet.)
Step 2: DR for one hour.
You are underway on course 315°T at 10 knots. The current is 090°T at 2.3 knots. What will be the course & speed being made good?
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Current
You are underway on course 315°T at 10 knots. The current is 090°T at 2.3 knots. What is the course & speed being made good?
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CMG/SMG
Step 3: Draw the Set & Drift Vector from the tip of the Course & Speed Vector
You are underway on course 315°T at 10 knots. The current is 090°T at 2.3 knots. What is the course & speed being made good?
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CMG/SMG
Step 4: Complete the Triangle
You are underway on course 315°T at 10 knots. The current is 090°T at 2.3 knots. What is the course & speed being made good?
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CMG/SMG
Step 4: Complete the Triangle
You are underway on course 315°T at 10 knots. The current is 090°T at 2.3 knots. What is the course & speed being made good?
CMG = 329° T
SMG = 8.2 kts
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Course & Speed
You wish to make good a course of 015°T and a speed of 8 knots. The current is
330°T at 3 knots. What is the course to steer and engine speed to turn?
Problem Type #3AGiven a desired CMG & SMG and a
known current, determine the course to steer & required engine speed.
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Current
Step 1: Plot the first position.
(If no position is given, use the center of a compass rose or plotting sheet.)
Step 2: Lay out the desired track (draw the CMG/SMG vector) for 1 hour.
You wish to make good a course of 015°T and a speed of 8 knots. The current is 330°T at 3 knots. What is the course to steer and engine speed to
turn?
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Current
You wish to make good a course of 015°T and a speed of 8 knots. The current is 330°T at 3 knots. What is the course to steer and engine speed to
turn?
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Current
You wish to make good a course of 015°T and a speed of 8 knots. The current is 330°T at 3 knots. What is the course to steer and engine speed to
turn?Draw the Set & Drift Vector from the 1st
position.
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Current
You wish to make good a course of 015°T and a speed of 8 knots. The current is 330°T at 3 knots. What is the course to steer and engine speed to
turn?Complete the Triangle
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Current
You wish to make good a course of 015°T and a speed of 8 knots. The current is 330°T at 3 knots. What is the course to steer and engine speed to
turn?Complete the Triangle
Course to Steer = 034° T
Required Engine Speed = 6.2 kts
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Current
You wish to make good a course of 015°T and a speed of 8 knots. The current is 330°T at 3 knots. What is the course to steer and engine speed to turn?
Alternate Procedure – Draw the S&D Vector Backwards from the CMG Vector
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Current
You wish to make good a course of 015°T and a speed of 8 knots. The current is 330°T at 3 knots. What is the course to steer and engine speed to turn?
Complete the TriangleCourse to
Steer = 034° T
Required Engine Speed = 6.2 kts
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Current
You wish to make good a course of 315°T. Your engine speed is 8 knots. The current is setting due north at 3 knots. What is the course to steer and speed made good along
the trackline?
Problem Type #3BGiven a desired CMG, a known current & your engine speed, determine the course to
steer & speed made good.
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Current
You wish to make good a course of 315°T. Your engine speed is 8 knots. The current is setting due north at 3 knots. What is the course to steer and speed
made good along the trackline?
Draw the CMG/SMG vector an indefinite length.
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Current
You wish to make good a course of 315°T. Your engine speed is 8 knots. The current is setting due north at 3 knots. What is the course to steer and speed made
good along the trackline?
Draw the Set & Drift vector from the center.
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Current
You wish to make good a course of 315°T. Your engine speed is 8 knots. The current is setting due north at 3 knots. What is the course to steer and speed made
good along the trackline?
Open dividers to engine speed.
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Current
You wish to make good a course of 315°T. Your engine speed is 8 knots. The current is setting due north at 3 knots. What is the course to steer and speed made
good along the trackline?
Swing an arc from the S&D vector to the CMG line.
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Current
You wish to make good a course of 315°T. Your engine speed is 8 knots. The current is setting due north at 3 knots. What is the course to steer and speed made
good along the trackline?
Complete the triangle.
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Current
You wish to make good a course of 315°T. Your engine speed is 8 knots. The current is setting due north at 3 knots. What is the course to steer and speed made
good along the trackline?
Complete the triangle.
Course to Steer = 300° T
SMG = 9.1 kts
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Introduction to Navigation
Questions?