Part cargo transportation is one of the most combinatorially difficult problems in commercial voyage planning. Unlike a full-vessel employment, the decision cannot be reduced to selecting one cargo and calculating one route, because several parcels may share the same vessel while having different ports, laycans, cargo characteristics and operational restrictions.
The value of an individual parcel therefore depends on the complete cargo combination. A cargo that looks attractive in isolation may create an additional port call, occupy a critical cargo space, conflict with another parcel or force a sequence that makes the overall voyage weaker.
One Optimization Problem, Different Physical Cargo Models
The commercial structure of Part Cargo is similar across different vessel and cargo types. The optimizer has to decide which cargoes should be combined, how the voyage should be sequenced and whether the resulting plan remains commercially and operationally feasible.
The physical feasibility problem, however, is different for different types of transportation. For this reason, Marine Solver includes three Part Cargo variants: Tanker, Bulk and General Cargo, each using its own cargo-space logic while remaining connected to the same voyage optimization framework.
Tanker Part Cargo
In tanker operations, the problem is strongly linked to tank allocation and cargo compatibility. It is not enough to know that the vessel has sufficient total capacity, because individual parcels must be placed into technically suitable tanks while respecting restrictions between cargoes and the configuration of the vessel.
The Tanker model can account for tank capacities, specific tank inclusions and exclusions, previous cargo history and compatibility rules. Tank grouping can also be used where technologically linked tanks need to be treated as a single operational cargo block.
Bulk Part Cargo
Bulk Part Cargo has a different physical structure, but the planning principle remains the same. Several parcels have to share the vessel while cargo intake, available cargo spaces and the loading and discharge sequence remain consistent with the complete voyage.
The model evaluates cargo allocation together with routing and timing rather than treating hold utilization as a separate calculation after the commercial plan has already been selected. This allows technically feasible cargo combinations to compete directly inside the same optimization problem as their commercial alternatives.
General Cargo Part Cargo
General Cargo introduces another level of physical complexity because cargo feasibility cannot always be described by weight or volume alone. A parcel may also have dimensions, required floor area, unit-based placement limitations or restrictions related to the geometry and accessibility of a cargo space.
Marine Solver therefore treats General Cargo as a separate physical model. Internal cargo spaces can be evaluated by weight, volume and usable area, while dimensional cargoes can also be checked against their actual size and the geometry of the available space.
When Weight and Volume Are Not Enough
General cargo can create situations where the vessel has sufficient theoretical capacity but the cargo still cannot be placed physically. Long, wide or unit-based cargoes may require a particular floor area, clearances between units or a specific arrangement that reduces the practically usable capacity of the space.
The model can therefore consider technological gaps and packing efficiency when evaluating unit-based dimensional cargo. This prevents a mathematically attractive allocation from being accepted when the cargo cannot realistically fit into the available internal space.
Vertical Access and Cargo Sequence
In General Cargo, placement can also affect the loading and discharge sequence. If one cargo occupies a space above another cargo, the lower cargo may need to be loaded earlier and discharged later for the plan to remain physically accessible.
Marine Solver links these vertical relationships with route and laycan feasibility. A cargo allocation can therefore be rejected not only because it exceeds capacity, but also because its physical placement conflicts with the chronological loading or discharge sequence.
Internal Spaces and Fixed Deck Cargo
Not every General Cargo parcel has to be automatically allocated by the solver. Cargoes can already have a fixed internal placement, and cargo carried on deck or in another externally defined position can remain fixed while the rest of the vessel is optimized around it.
This is especially useful when the optimization begins from an operational state that already exists rather than from an empty vessel. The model can preserve fixed cargo allocations while searching for feasible combinations for the remaining cargo opportunities.
Capacity Is Not the Same as Feasible Capacity
This distinction applies to all three Part Cargo variants, although the reason may be different. A tanker may have unused capacity but no compatible tank, a bulk vessel may have insufficient usable space for a particular parcel combination, and a general cargo vessel may have enough weight capacity but insufficient volume, floor area or physical access.
The relevant question is therefore not simply how much capacity remains. The real question is how much of that capacity is still usable for the next cargo without making the rest of the voyage infeasible.
Batch Optimization Instead of Cargo-by-Cargo Selection
A common Part Cargo problem is a batch scenario where several cargoes are accumulated across a loading region and then discharged through another sequence of ports. The objective is not merely to accept the maximum number of parcels, because every additional call changes sailing distance, port time and the economics of the complete chain.
Marine Solver evaluates the complete cargo set as one optimization problem. Cargo selection, routing, loading sequence, discharge sequence and the relevant physical cargo-space constraints are considered together rather than solved as independent stages.
Routing and Cargo Allocation Are Connected
A commercially attractive route can become impossible once the actual cargo allocation is considered. The opposite is also true, because an excellent stowage solution may belong to a voyage sequence that is commercially weak or impossible under the required laycans.
This is why Marine Solver connects cargo-space feasibility with voyage feasibility. The selected cargo combination has to work physically inside the vessel and operationally across the complete route at the same time.
Onboard Cargo Changes the Starting Point
Part Cargo planning does not always begin with an empty vessel. A ship may already carry one or several parcels when another commercial opportunity appears, or the complete cargo may already be onboard while the remaining decision concerns the discharge sequence.
Marine Solver's Onboard Cargo logic allows the existing cargo state to become part of the initial conditions of the optimization. Cargoes already onboard remain in the model with their existing obligations and occupied cargo spaces while new decisions are evaluated around them.
Loading Along an Active Voyage
A particularly interesting case appears when the vessel is already carrying cargo but still has usable capacity for additional parcels. The question is no longer whether the new cargo fits into an empty vessel, but whether it can be added without damaging the existing route, discharge sequence or physical cargo allocation.
Marine Solver evaluates the new opportunity inside the complete voyage structure. This makes it possible to analyze additional loading during an active voyage instead of rebuilding the commercial problem as if the vessel were starting from ballast.
Sequence Is Part of the Decision
Two voyages carrying the same cargoes can produce different results simply because the loading or discharge order is different. Sequence affects sailing distance, port calls, waiting, cargo accessibility and the moment when occupied cargo spaces become available again.
For this reason, the sequence is part of the optimization problem itself. The system can evaluate alternative loading and discharge structures rather than assuming that the operational order is already fixed before the calculation begins.
Alternative Cargo-Space Plans
A feasible cargo combination may allow more than one technically valid allocation. In these situations, one arrangement does not necessarily have to be treated as the only possible answer, especially when another layout provides more flexibility for the subsequent voyage operations.
Marine Solver can generate alternative cargo-space assignments for comparison. The exact representation depends on the Part Cargo variant, but the purpose is the same: to make the physical side of the solution visible rather than hiding it inside the optimization engine.
Commercial Constraints Remain Part of the Same Model
Physical feasibility does not replace commercial feasibility. Laycan windows, vessel position, port operations, waiting, voyage duration and commercial restrictions remain part of the same problem while cargo placement and sequence are being evaluated.
This is important because a technically valid cargo plan can still be commercially impossible. The optimization result has to satisfy both sides of the decision before the cargo combination can be considered viable.
Economics and Environmental Exposure
Different Part Cargo combinations can create very different voyage structures even when they use the same vessel. Changes in port sequence and cargo selection affect sailing time, waiting, fuel consumption and voyage cost, while the resulting environmental exposure also changes with the route.
Marine Solver evaluates these factors within the same model, including port and canal costs, fuel consumption, EU ETS exposure, CII/AER assessment and FuelEU Maritime planning metrics. This allows the commercial result and the environmental consequences of the selected cargo chain to be evaluated together.
Different Objectives Can Produce Different Cargo Combinations
There is no single definition of the best Part Cargo voyage. A combination that minimizes operating cost may differ from the combination that maximizes profitability, reduces non-productive time or produces a lower emissions result.
Marine Solver can therefore evaluate the same cargo set under different optimization objectives. The comparison shows not only how the final numbers change, but also how the selected objective changes the cargo mix, voyage sequence and use of the vessel.
Why Manual Planning Becomes Difficult So Quickly
The number of possible alternatives grows very quickly as cargoes and cargo spaces are added. Every parcel can introduce new route combinations, placement alternatives and sequence dependencies while simultaneously making some previously feasible combinations impossible.
With Tanker, Bulk and General Cargo, the exact source of complexity is different, but the mathematical effect is the same. The task becomes a connected combinatorial problem where routing, cargo selection and physical feasibility influence one another.
Pre-Fixture Planning with Physical Reality Included
Part Cargo sits at the boundary between commercial voyage planning and the physical reality of the vessel. It does not replace detailed onboard cargo execution, but it allows cargo-space constraints to influence the commercial decision before the voyage structure is fixed.
This is the main reason the physical models matter. A parcel becomes a real commercial opportunity only when it can form part of a complete voyage that is both technically feasible and commercially meaningful.
Conclusion
Part Cargo optimization is not about filling unused space. It is about finding a strong combination of cargoes, route, sequence and cargo allocation while recognising that every individual decision changes the possibilities that remain available afterwards.
Marine Solver approaches this through three physical cargo models for Tanker, Bulk and General Cargo, connected to one voyage optimization framework. The result is not simply a fuller vessel, but a complete cargo and voyage structure that can be evaluated as one decision.
Explore other Marine Solver planning models:
For full-vessel cargo selection and voyage-chain planning, read about the
Sole Cargo Module.
For transportation planning under contractual lifting obligations, explore
COA Cargo Optimization.
For fleet-level transportation program coverage, see
Trader Fleet.