Machinery, Propulsion and Auxiliaries: Rule Performance, Redundancy and Emissions Control
Machinery questions concentrate on the performance the rules demand rather than on thermodynamics: how fast the rudder must move, what redundancy is required, what happens when the machinery space is periodically unattended, and how MARPOL Annex VI limits what leaves the funnel.
Steering gear and manoeuvring
SOLAS II-1 requires main and auxiliary steering gear, with duplicate control from the navigating bridge and the steering gear compartment and clear changeover instructions at both. The main gear must steer from 35 degrees on one side to 35 degrees on the other at maximum ahead service speed and, under the same conditions, from 35 degrees on either side to 30 degrees on the other in not more than 28 seconds. The auxiliary gear must put the rudder from 15 degrees on one side to 15 degrees on the other in not more than 60 seconds with the ship at half ahead speed or 7 knots, whichever is greater. Ships must also be able to go astern with sufficient power, and steering gear drills are held at least every three months.
Redundancy and unattended operation
Propulsion arrangements must allow essential services to be maintained with one auxiliary set out of action. Periodically unattended machinery spaces require alarms to the duty engineer and the bridge, a dead-man alarm, and documented procedures; the arrangement reduces watchkeeping, not the obligation to detect and respond to faults.
Emissions and fuel
MARPOL Annex VI sets sulphur limits of 0.50 per cent globally (since 1 January 2020) and 0.10 per cent in emission control areas, with the Mediterranean Sea SOx ECA effective 1 May 2025. Equivalent means such as exhaust gas cleaning systems are permitted if approved and verified. NOx Tier III applies to ships built on or after 1 January 2016 when operating in NOx emission control areas. The SEEMP, EEDI/EEXI and carbon intensity rating sit alongside the technical file for engines.
Worked example
On trial, a rudder moves from 35 degrees port to 35 degrees starboard in 32 seconds at maximum ahead service speed. That is 70 degrees in 32 seconds, or 2.19 degrees per second. The rule for that leg is 65 degrees in 28 seconds, which needs 2.32 degrees per second, so the observed rate fails the criterion even though the full swing looks rapid.
Traps
Confusing the 28-second main gear requirement with the 60-second auxiliary requirement; assuming one power unit satisfies redundancy; believing unattended operation removes alarm obligations; ignoring that Annex VI compliance must be demonstrated by bunker delivery notes, sampling and records.