Engine Controls & Measurement — Bridge to Shaft
How control moves between stations, how torque is weighed electrically, and how computers draw cards.
Key Principles at a Glance 5 points
- Control flows bridge → control room → local, but emergency takeover works running or stopped while return to remote needs a stopped engine.
- Torque is twist measured electrically: four shaft strain gauges in a bridge, slip rings or frequency telemetry out, times revs equals power.
- Computer cards beat mechanical above 120 rpm: transducer on the cock plus crank sensor draws power and crank-angle diagrams at any speed.
- Overlaid cylinders in different colours expose the weak unit instantly; injection faults read straight off the crank-angle trace.
- The MC dip just after TDC is design (35 bar crosshead protection), not fault — tune injection only after scavenge, air and rings check out.
1. Changeover Drills
Idea in one line: control is a token passed between stations — the engine only obeys the holder, and the handover rules differ by direction.
On an automated ship the engine can be run from the bridge, the engine control room, or the local emergency stand. Remote stations lease control; the local stand owns it.
| Handover | Conditions |
|---|---|
| To bridge | Control selector on Bridge; local levers in REMOTE; no alarms or cut-outs that would trip an interlock; starting-air main valve and auxiliary blowers in AUTO, not misplaced. |
| To control room | Local levers in REMOTE (ECR); automation manufacturer's start sequence applies for the fitted system. |
| Emergency takeover | Allowed running or stopped — notch the fuel lever out of REMOTE into the linkage; prove overspeed protection; watch speed continuously and trim fuel by hand. Bridge keeps an independent emergency stop regardless. |
| Return to remote | Only with the engine stopped — remote is never re-engaged onto a running engine. |
Start from the stand: blowers on, telegraph answered, direction set, fuel lever to start, manoeuvring lever held at START till running, fuel eased to speed. Stop: fuel lever down to stop, full stop answered. Plants differ — the maker instructions rule the specifics.
2. Weighing Torque Electrically
Idea in one line: the shaft is a spring you cannot see — twist it, read the stretch electrically, multiply by speed for power.
Indicated power lives in the cylinder; brake power lives at the flange. The torsionmeter bridges them without stopping the ship: four strain gauges bonded to the shaft form a bridge whose resistance shifts with twist.
Twist strains the gauges: torque twists the shaft, the four bonded gauges stretch and compress, bridge resistance shifts with strain.
Signal leaves the spinning shaft: older sets use brushes and slip rings; newer sets convert resistance to frequency on the shaft and telemeter it contact-free to a digital receiver.
Torque × revs = shaft power: continuous power truth while running — no dynamometer, no stopped ship.
3. Computer Cards at Any Speed
Idea in one line: a pressure transducer plus a crank-angle sensor replaces the bouncing pencil — cards at any speed, overlaid in colour.
Mechanical indicators shake out above roughly 120 rpm, and even skilled draw-cards top out near 450. The computer set has no such ceiling: a transducer screws onto the indicator cock, a crank sensor on flywheel or prop shaft reports angle, and a processor marries the two.
Record: cock opened, blow soot through, store each cylinder's pressure-against-angle trace in the processor.
Download: traces come down as power cards and crank-angle diagrams — every cylinder overlaid in its own colour.
Read injection off the angle trace: the weak unit and the faulty injection event show at a glance against healthy sisters.
Slow-speed MC combustion is deliberately delayed past TDC, capping pressure near 35 bar to protect the crosshead — the small dip after TDC is protection, not pathology. Fine-tune injection timing for lost power only after scavenge cleanliness, air supply, liner and rings, and stuffing box check out.