USCG OIM flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

BMEP formula

Brake mean effective pressure = (brake power × 60) / (stroke × bore area × rpm × number of cylinders). It compares engine loading independent of size and speed.

Mechanical efficiency

The ratio of brake power to indicated power, expressed as a percentage. It falls when friction or pumping losses rise, indicating bearing, piston or valve problems.

Specific fuel consumption

Fuel mass flow per unit brake power, usually g/kWh. A slowly rising trend at constant load signals fouling, worn injectors, or restricted combustion air.

Turbocharger surging

Unstable airflow causing rapid pressure pulsations, often on rapid load increase or fouled air passages. Prevent by gradual loading and cleaning air cooler and scavenge spaces.

Cylinder oil versus system oil

Two-stroke crosshead engines use total-loss cylinder oil for liners and a separate circulating system oil for bearings. Four-stroke trunk engines use one sump oil for both.

Boiler purge before ignition

Forced-air purge of the furnace before lighting off clears unburnt fuel. Skipping purge risks a furnace explosion; flame failure trip must be tested first.

Auxiliary boiler low-water trip

Cuts the burner when drum level falls below a safe limit to protect tubes from overheating. It must be tested and proved before lighting off.

Three-phase power formula

Active power P = √3 × line voltage × line current × power factor. Apparent power S = √3 × V × I, and reactive power Q = √3 × V × I × sin φ.

Generator paralleling conditions

Before closing the breaker, voltage, frequency, phase sequence and phase angle must match the busbar. kW shares by governor droop; kVAr shares by excitation adjustment.

Governor droop and load sharing

Droop is the frequency fall from no load to full load. A generator with lower droop takes a larger share of kW load for the same frequency deviation.

Insulation resistance minimum

For a 440 V system, about 1 MΩ at 500 V DC test is the usual minimum. Lower readings indicate moisture, dirt, or cable damage and require investigation.

Preferential trip

An interlock that sheds non-essential loads such as HVAC or galley when a generator overloads or one generator is lost, protecting the remaining generator.

4-20 mA live-zero loop

Analogue signal where 4 mA is zero and 20 mA full scale. A reading of 0 mA indicates a broken wire or failed transmitter, allowing fault detection.

Insulated system earth fault

On an IT distribution system a single earth fault does not trip but must be located and cleared. An insulation monitoring device alarms and indicates the faulted circuit.

Lead-acid float voltage

Float charge for lead-acid cells is about 2.25 V per cell; equalising charge about 2.4 V per cell. Overcharging causes gassing and water loss.

PLC analogue input scaling

A 4-20 mA signal is scaled in the PLC to engineering units, for example 4 mA = 0 bar and 20 mA = 10 bar. Verify scaling before trusting displayed values.

Planned maintenance intervals

Intervals are set by running hours, calendar time, or condition monitoring such as vibration and oil analysis. Deferral requires chief engineer authorisation and record.

Oil analysis wear metals

Iron indicates general wear, chromium rings or liners, sodium coolant ingress, and copper bearing wear. Rising trends trigger inspection before failure.

ISO 10816 vibration zones

Zones A to D classify machinery vibration severity. Zone C or D readings, or a rising trend, require investigation before continued running.

Enclosed space entry test

Test atmosphere before entry: oxygen about 20.9%, LEL below 1%, and H2S and CO within limits. Requires permit, ventilation and a standby man outside.

Lockout tagout

Isolate the energy source, prove dead, apply lock and tag, then test the isolation. The person working applies their own lock before starting work.

Hydrostatic test pressure

Piping is usually tested at 1.5 times design pressure hydrostatically unless the applicable code specifies otherwise. Relief valves are set and sealed to design pressure.

Bearing clearance measurement

Measured by bridge gauge or lead wire and compared with the maker's wear limit. Exceeding the limit requires renewal before reassembly.

Torque tightening practice

Follow the manual's tightening sequence and torque values using a calibrated torque wrench. Record the calibration date and the values applied.

Hot work permit

Requires gas-free certificate, removal of combustibles, fire watch, and checks of adjacent spaces before any welding, cutting or grinding is permitted.

Oily water separator limit

MARPOL Annex I allows overboard discharge only through a 15 ppm oily water separator with monitoring. All transfers and disposals are recorded in the oil record book.

MARPOL Annex VI sulphur limits

Global sulphur limit is 0.50% m/m and 0.10% m/m in emission control areas. Bunker delivery notes must be retained for three years.

Emergency generator start time

SOLAS requires the emergency generator to start and take load automatically within 45 seconds of a blackout, supplying emergency lighting, steering and radio.

STCW watch handover

The engineer on watch must be fit for duty and brief the relief on machinery status, abnormal readings and standing orders before handing over.

Fixed CO2 release precautions

Before release, evacuate the space, close boundaries, account for all persons, and confirm the fire is not re-ignitable by personnel. Release is a last resort.

Garbage record book

MARPOL Annex V requires recording discharges and incinerations. Plastics must never be discharged to sea; retention is typically two years.

Oil record book entries

Entries are made without delay for every transfer, disposal or discharge. Falsification is a criminal offence and the chief engineer is accountable.