Current triangle CTW and SMG Practice Questions

1. In current triangle terminology, what does 'CTW' stand for?

• A.Current Track and Way
• B.Course Through the Water✓
• C.Corrected Track to Waypoint
• D.Course True West

Why: CTW stands for Course Through the Water, which is the direction the vessel's bow points relative to the water mass it is traveling through, also known as the heading steered.

2. A vessel steers 045°T at 12 knots through the water. The current sets 135°T at 3 knots. Without plotting, the course made good will be:

• A.Exactly 045°T, because the heading does not change
• B.To the right (clockwise) of 045°T due to the current's easterly component✓
• C.To the left (counterclockwise) of 045°T due to the current's southerly component
• D.Identical to 045°T only if the current speed equals boat speed

Why: A current setting 135°T has both a southerly and easterly component. The easterly component deflects the vessel's track to the right (clockwise) of the steered course of 045°T, resulting in a course made good greater than 045°T.

3. A vessel steers 000°T at 10 knots STW with a current setting 090°T at 3 knots. What is the approximate speed made good (SMG)?

• A.10.0 knots
• B.13.0 knots
• C.10.4 knots✓
• D.7.0 knots

Why: With perpendicular current components, SMG = √(10² + 3²) = √(100 + 9) = √109 ≈ 10.4 knots. The SMG exceeds the STW when the current has a forward component.

4. If a favorable current (same direction as CMG) is acting on a vessel, what is the effect on SMG compared to STW?

• A.SMG equals STW regardless of current direction
• B.SMG is less than STW because the current opposes steerage
• C.SMG is greater than STW because the current adds to the vessel's progress✓
• D.SMG and STW are only equal when the current is at right angles to the track

Why: When the current sets in the same direction as the course made good, it adds to the vessel's speed through the water, so SMG exceeds STW. This is a favorable or fair current.

5. A vessel is steered 270°T at 9 knots STW. The current sets 270°T at 3 knots (fair current directly astern). What is the CMG and SMG?

• A.CMG 270°T, SMG 6 knots
• B.CMG 270°T, SMG 9 knots
• C.CMG 270°T, SMG 12 knots✓
• D.CMG 267°T, SMG 12 knots

Why: When the current is directly fair (same direction as heading), the vectors are collinear and add directly. CMG remains 270°T and SMG = 9 + 3 = 12 knots. There is no angular deflection.