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

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 & Drift

Current Triangle Course & Speed CMG & SMG Set & Drift If you know any 2 sides, you can solve for the 3 rd side.

Current Triangle Course & Speed CMG & SMG Set & Drift If you know the Course & Speed And the Set & Drift You can get the CMG & SMG Estimated Position

Current Triangle Course & Speed CMG & SMG Set & Drift If you know the Course & Speed You can solve for the Set & Drift And the CMG & SMG

Current Triangle Course & Speed CMG & SMG Set & Drift You can solve for the Course & Speed And 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 2 nd 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 –

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 –

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 – CMG/SMG Set & 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 CMG/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 CMG/SMG Distance = 0.6 nm 0.6 nm 41 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 #2 Given 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?

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?

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 #3A Given 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?

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?

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.

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

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

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

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

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 #3B Given a desired CMG, a known current & your engine speed, determine the course to steer & speed made good.

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.

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.

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.

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.

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.

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

Introduction to Navigation Questions?