Current sailing diagram construction Practice Questions

1. When constructing a current triangle to find the course to steer, which vector is drawn first from the departure point?

• A.The vessel's speed through the water vector
• B.The current vector (set and drift)
• C.The course made good (CMG) vector toward the destination✓
• D.The resultant speed made good vector

Why: The course made good (CMG) vector is drawn first from the departure point toward the destination. The current vector is then applied from the departure point, and the vessel's water-speed arc is swung from the end of the current vector to close the triangle.

2. A vessel must make good a course of 090°T at a speed made good of 10 knots. The current is setting 180°T at 2 knots. To construct the current triangle, which statement is correct?

• A.The current vector is drawn in the direction 000°T for 2 units
• B.The current vector is drawn in the direction 180°T for 2 units from the departure point✓
• C.The current vector is drawn in the direction 180°T for 10 units
• D.The vessel speed vector is drawn parallel to the current vector

Why: The current vector is plotted from the departure point in the direction of the set (180°T) for a length proportional to the drift (2 units). This vector represents the water movement the vessel must overcome.

3. A navigator wants to proceed directly to a destination bearing 270°T at 15 miles with a 2-knot northerly current (set 000°T). The vessel's STW is 10 knots. What must the navigator determine by constructing the current triangle?

• A.The new compass deviation caused by the current
• B.The course through the water to steer so the CMG remains 270°T✓
• C.The adjusted chart scale to account for set
• D.The estimated drift based on the magnetic bearing

Why: The current triangle is used to find the course through the water (CTW) that, when combined with the current vector, produces the desired course made good (CMG) of 270°T. The navigator must steer slightly south of 270°T to counteract the northerly current.

4. In a current triangle problem where the desired CMG and STW are known but the current is unknown, which two positions are needed to determine the current vector?

• A.The compass heading and the chart magnetic variation
• B.The dead reckoning position and the observed (fix) position for the same time✓
• C.The departure sounding and the arrival sounding
• D.The charted current arrow and the tidal prediction table entry

Why: The current vector is derived from the difference between the DR position (where the vessel would be without current) and the actual observed fix for the same time. The vector drawn from DR to fix gives the set and drift of the current.

5. In current triangle construction, if the vessel's STW arc (swung from the tip of the current vector) does not intersect the CMG line, what does this indicate?

• A.The navigator made a plotting error in applying variation
• B.The vessel does not have sufficient speed to make good the desired course against the current✓
• C.The current is favorable and no course correction is needed
• D.The scale of the chart is too small for accurate current work

Why: If the STW arc does not reach the CMG line, the vessel's speed through the water is insufficient to overcome the cross-track component of the current and maintain the desired course made good. The navigator must either increase speed or accept a different CMG.