Single Main Engine — Basic Understanding
All Single Main Engine vessels have the following arrangement based on the hull's exact centerline:
1) Propeller shaft center is positioned on the centerline
2) Rudder center is positioned on the centerline
For a Single Main Engine vessel, course changes are achieved ONLY by adjusting the rudder (steering) angle, up to 35° to port or starboard.
Twin Main Engine — Basic Understanding
All Twin Main Engine vessels have each propeller shaft and rudder centered at the quarter-beam position (half of half the hull's beam width).
1) Each propeller shaft center is at quarter-beam
2) Each rudder center is at quarter-beam
Both port and starboard engines must produce equal thrust power, and both rudder (steering) angles must be equal, for the vessel to proceed on a straight heading.
Normal Operation — Both Engines Running
Lever Position
P: AH 90 | S: AH 90
Steering Handle
Combination Handle: 0° (Midship)
Both engines at Ahead 90 (full power). Steering combination handle at 0° (midship). Equal thrust from both propellers ensures the vessel maintains a straight course.
Vessel proceeds straight ahead on the intended heading. Both engines provide equal thrust; no steering correction needed.
Starboard Engine Disabled — Ahead
Lever Position
Port: AH 90 (Starboard: OFF)
Steering Handle
Combination Handle: P 90° ~ S 90°
With only the port engine running, the thrust is offset from the centerline. The vessel will naturally turn (yaw) to the STARBOARD side.
Apply 10°~15° steering angle to PORT to maintain a straight course. (Exact angle varies by vessel.)
Starboard Engine Disabled — Ahead (Controls)
Steering
Governor / Clutch
• Port Lever: AH 90 (Full Ahead)
• Starboard Lever: 0 (Engine OFF)
• Steering Combination Handle: P 90° ~ S 90°
To maintain straight heading:
Combination Handle → Port 80°~85°
The vessel will yaw to STARBOARD due to asymmetric thrust. Correct by applying 10°~15° port steering. The exact correction angle varies slightly between different vessels.
Starboard Engine Disabled — Astern (Z-Peller)
Lever Position
Port: AS 90 (Astern Full)
Steering Handle
Combination Handle: P 90° ~ S 90°
When the starboard engine is disabled and only the port engine is used for navigation:
1) Steering lever position: AS 90
2) Astern power controlled by main engine RPM
3) Astern direction controlled by Steering Combination Handle
Stern swings to STARBOARD, bow swings to PORT. Use combination handle to control reverse direction.
Starboard Engine Disabled — Astern (Controls)
Steering
Governor / Clutch
• Port Lever: AS 90 (Full Astern)
• Starboard Lever: 0 (Engine OFF)
• Steering Combination Handle: P 90° ~ S 90°
To maintain straight astern heading:
Combination Handle → Starboard 80°~85°
The vessel will yaw to STARBOARD when going astern. Apply 10°~15° steering correction to PORT side to maintain a straight reverse course. Correction angle varies slightly between vessels.
Port Engine Disabled — Ahead
Lever Position
Starboard: AH 90 (Port: OFF)
Steering Handle
Combination Handle: P 90° ~ S 90°
With only the starboard engine running, the thrust is offset from the centerline. The vessel will naturally turn (yaw) to the PORT side.
Apply 10°~15° steering angle to STARBOARD to maintain a straight course. (Exact angle varies by vessel.)
Port Engine Disabled — Ahead (Controls)
Steering
Governor / Clutch
• Starboard Lever: AH 90 (Full Ahead)
• Port Lever: 0 (Engine OFF)
• Steering Combination Handle: P 90° ~ S 90°
To maintain straight heading:
Combination Handle → Starboard 80°~85°
The vessel will yaw to PORT due to asymmetric thrust from the starboard engine only. Correct by applying 10°~15° starboard steering. The exact correction angle varies between vessels.
Port Engine Disabled — Astern (Z-Peller)
Lever Position
Starboard: AS 90 (Astern Full)
Steering Handle
Combination Handle: P 90° ~ S 90°
When the port engine is disabled and only the starboard engine is used for navigation:
1) Steering lever position: AS 90
2) Astern power controlled by main engine RPM
3) Astern direction controlled by Steering Combination Handle
Stern swings to PORT, bow swings to STARBOARD. Use combination handle to control reverse direction.
Port Engine Disabled — Astern (Controls)
Steering
Governor / Clutch
• Starboard Lever: AS 90 (Full Astern)
• Port Lever: 0 (Engine OFF)
• Steering Combination Handle: P 90° ~ S 90°
To maintain straight astern heading:
Combination Handle → Port 80°~85°
The vessel will yaw to STARBOARD when going astern with port engine disabled. Apply 10°~15° correction to PORT to maintain a straight reverse course. Correction angle varies between vessels.