Engineering & Technology · Marine, Ocean & Offshore Engineering

Marine power, auxiliary systems and integrated operations

Two generators may supply the same bus, yet a shared cooling failure can disable both. A marine system’s useful service depends on the connections among power, auxiliaries, controls and the physical environment. Counting installed machines alone does not reveal those dependencies.

Use Fluid Engineering, Civil & Structural Engineering and Materials Selection & Degradation for balances, structural response and environmental mechanisms. Physics fluid dynamics and continuum materials provide further preparation. No example supplies a marine operating procedure, stability certificate, mooring design, electrical architecture approval or environmental permission.

Back to the chapter

After reading, you can

Connect propulsion, electrical supply, auxiliaries and controls through their capacity and dependency requirements, including the limits of redundancy.

The useful function crosses several subsystems

A propulsion arrangement may transmit mechanical power through gearing and shafts, or convert it through generators, electrical distribution, converters and motors. Each path has losses and operating limits. Its thermal management, lubrication, control and supporting services also need to function for the specified condition.

Other demands can include steering, navigation and communications, equipment, accommodation, fluid handling and cooling. Distinguish essential services from loads whose interruption changes only the mission output. Water ingress, electrical faults or failed sensors can affect several functions at once. A functional dependency diagram explains what must be available; it is not a wiring or piping drawing.

Redundancy must deliver the required service

For an invented electrical account, supply two sources each capable of 100 kW at a common reference plane. A defined full-service load is propulsion 120, accommodation 20, auxiliaries 10 and controls 5 kW: total 155 kW. The two-source capacity exceeds that total by 45 kW, assuming the sources and distribution can actually share the load.

One remaining source cannot deliver the full 155 kW. An alternative supplied service state with propulsion demand 50 kW gives total 85 kW, within a 100 kW capacity. That arithmetic does not establish whether the reduced propulsion is enough for manoeuvring or another critical task. The service definition and physical performance must agree before a source can count as adequate redundancy.

An original random-instant availability model

Now define a separate abstract service that either source alone can supply. At a randomly chosen instant, each source has supplied unavailability q=0.02. Assume their states are independent and each supplies the function whenever available. Both are unavailable with probability 0.02²=0.0004, giving source-pair availability 0.9996.

Add a shared support function with supplied availability 0.99, independent of both source states, required whenever service is delivered. Complete-service availability becomes 0.99×0.9996=0.989604. The diagram shows the common function after the parallel alternatives. These invented probabilities describe a random-instant model, not measured equipment or the probability of completing a voyage.

Each source has unavailability 0.02 and either alone suffices for this abstract service. Independent source states give pair availability 1−0.02²=0.9996. Independently required common support availability 0.99 yields service availability 0.989604 and unavailability 1.0396%. Connections indicate functional dependence, not physical wiring or switching time.

Identify what the parallel formula assumes

Without the common support, the model’s unavailable fraction is 0.04%. With it, the fraction is 1−0.989604=1.0396%. Adding more nominally independent sources cannot remove a support failure that disables every route. Shared faults, location, fuel, cooling or control can also undermine the independence assumed for the sources.

A real evidence plan examines capacity, faults, recovery and the resulting service during interruptions. Switching and starting take time; repair support and access affect restoration. Preserve actual failure and maintenance records and test the intended function under defined conditions. The simplified dependency account supplies no architecture approval or operating sequence.

Try the reasoning

Does 200 kW installed capacity guarantee full service after loss of one 100 kW source?
Show the answer and reasoning
No. The declared 155 kW load exceeds the remaining 100 kW capacity.
Why multiply shared-support availability by pair availability here?
Show the answer and reasoning
Both the support and at least one source are required, and independence between their states is an explicit assumption.
Is 0.989604 the probability of a successful six-hour mission?
Show the answer and reasoning
No. It is random-instant availability under a supplied state model; mission completion also depends on time history, recovery and the defined service.

What to carry forward

Check delivered capacity and complete functional dependencies before using redundancy to claim a continuing marine service.

References

Teaching resources and research supporting this lesson’s explanations and examples.