navigation nau 102 lesson 28. current sailing the horizontal movement of the sea surface. current...
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Current Sailing Factors Ocean Current Tidal Current Wind-driven Current Wind SeasTRANSCRIPT
Navigation
NAU 102
Lesson 28
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.
Current Sailing
Factors
•Ocean Current•Tidal Current•Wind-driven Current •Wind•Seas
Current Sailing
Factors
•Compass Errors•Steering Errors•Engine Calibration Errors •Speed Log Errors•Fouled Bottom•Unusual Trim
Current Sailing
Current
The combined effect on a vessel of all the factors.
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
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.
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.
Current Triangle
Course & Speed
CMG & SMG
Set &
Drif
t
Current TriangleCourse & Speed
CMG & SMG Set &
Drif
t
If you know any 2 sides, you can solve for the 3rd side.
Current Triangle
Course & Speed
CMG & SMG Set &
Drif
t
If you know the Course & SpeedAnd the Set & Drift
You can get the CMG & SMG
Estimated Position
Current Triangle
Course & Speed
CMG & SMG Set &
Drif
t
If you know the Course & Speed
You can solve for the Set & DriftAnd the CMG & SMG
Current Triangle
Course & Speed
CMG & SMG Set &
Drif
t
You can solve for the Course & SpeedAnd the Set & Drift
If you know the CMG & SMG
Current Triangles
Can be solved using:
Charts
Universal Plotting Sheets
Radar Plotting Sheets
Maneuvering Boards
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?
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
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
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
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
1000CMG/SMG
Set = 137° T
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
1000CMG/SMGDistance = 0.6 nm
0.6 nm41 min X 60 min/hrDrift = = 0.9 kts
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).
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?
CurrentYou 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/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?
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/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
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.
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?
CurrentYou 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?
CurrentYou 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.
CurrentYou 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
CurrentYou 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
CurrentYou 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
CurrentYou 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
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.
CurrentYou 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.
CurrentYou 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.
CurrentYou 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.
CurrentYou 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.
CurrentYou 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.
CurrentYou 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
Introduction to Navigation
Questions?