How Floating Dry Docks Work

Floating drydocks are buoyant structures that lift other vessels clear of the water through control of ballast water.

Strategic Advantages of Floating Dry Docks

Floating dry docks are widely used and familiar to many shipyards and dockmasters. Their operating principles are well understood, and they remain a common choice in locations where permanent infrastructure is impractical.

Limitations and Risk Considerations

Floating dry docks are inherently constrained in ways that affect throughput, scheduling, safety, and environmental performance. They are subject to structural limitations, tidal dependence, stability and ballasting challenges, exposure to weather conditions, complex mooring requirements, limited ability to transfer vessels to land, single-asset throughput constraints, schedule cascade risk, high maintenance and operational costs, and potential discharge of contaminated ballast water.

These limitations become more pronounced as shipyard demand increases or schedules tighten.

According to Kaup, Łozowicka, and Blatnický (2018), docking operations conducted using floating docks and graving docks have experienced technical failures, human error, environmental impacts, and financial losses, including in facilities operating under established procedures.

When Floating Dry Docks Are Typically Selected

Floating dry docks are often selected where geographic constraints limit fixed infrastructure or where existing operational familiarity is prioritized.

How Graving Docks Work

Graving docks are fixed basins constructed into the ground. Vessels enter the dock, gates are sealed, and water is pumped out to expose the hull.

Strategic Advantages of Graving Docks

Graving docks provide a stable, enclosed environment and have historically supported large naval vessels and complex maintenance programs. Because they are constructed as fixed basins, graving docks can be built to virtually any length, allowing them to accommodate very large ship classes where floating dry docks or shiplift systems may become increasingly challenging to scale economically.

In locations with favorable subsurface conditions, graving docks can offer a durable, long-term solution for high-capacity naval MRO operations. When geology, vessel requirements, and long-term operational plans align, graving docks may provide a viable approach for servicing the largest vessels in a fleet.

Limitations and Risk Considerations

Graving docks introduce several structural and site-dependent constraints that influence long-term shipyard planning and operations. Construction feasibility and cost are highly dependent on local geology, with unfavorable subsurface conditions significantly increasing complexity, cost, or risk, and in some cases making graving dock construction impractical.

In regions with seismic activity, graving docks may also require extensive seismic design, reinforcement, and certification measures to manage ground motion, soil liquefaction, and structural integrity risks. These requirements can further increase construction complexity, cost, and regulatory burden over the life of the facility.

Graving docks typically involve high certification and regulatory compliance costs, along with significant upfront capital investment driven by large-scale civil works. As permanent infrastructure, they offer limited adaptability once constructed, requiring extensive upfront planning to ensure sustained utilization over their service life.

Operational throughput is often constrained to one or two vessels at a time, which can limit concurrent maintenance activity and increase schedule coupling. In addition, graving dock operations risk pumping dirty or contaminated water into the surrounding environment, creating ongoing environmental management and compliance considerations.

These constraints shape not only cost and schedule, but how shipyards scale, adapt, and manage risk over time.

When Graving Docks Are Typically Selected

Graving docks are often chosen where long-term permanence is required, heavy load concentrations are anticipated, and where site conditions support large fixed infrastructure investments.

For many shipyards, the question is no longer whether dry docks work, but whether their inherent constraints align with modern operational and lifecycle requirements.

Throughput limitations, scheduling interdependence, environmental exposure, and long-term cost predictability are driving interest in alternative approaches to docking, berthing, and vessel transfer.

Shiplift and transfer systems represent a different model, one that separates vessel berthing from repair timelines and emphasizes flexibility, redundancy, and land-based maintenance workflows.

How the OmniLift^® Shiplift Works

The OmniLift® shiplift is a permanent lifting and transfer system that raises vessels and moves them to onshore berths, where maintenance and repair activities take place on hard stand areas in the shipyard.

How the OmniLift Aligns with Modern Naval Requirements

Based on internal operational analysis, the OmniLift system offers several performance and planning advantages for modern shipyards. It delivers the lowest berthing and launching cost per vessel and minimizes total lifecycle cost over the system’s service life. The OmniLift provides superior flexibility, with overall capacity determined by the number of onshore berths rather than a single docking asset. Scheduling is independent across projects, meaning delays on one vessel do not cascade to others. Yard logistics and access are improved, allowing vehicles, equipment, and materials to move efficiently around vessels during maintenance. Transfer operations do not require mooring, and the system is operated through simple control systems that do not rely on specialized operational skill sets.

When comparing the OmniLift® system to floating dry docks, key operational differences emerge in how capacity, risk, and environmental exposure are managed. Floating dry docks concentrate capacity, scheduling, and operational risk into a single asset, whereas the OmniLift distributes work across multiple onshore berths, reducing dependency on any one project. Floating dry docks are inherently sensitive to weather and stability conditions, while the OmniLift mitigates these variables by operating primarily on land. In addition, floating dry dock operations require ballasting, a time-consuming process that can result in contaminated water being discharged into surrounding waterways. The OmniLift instead utilizes a steel platform and hydraulic chain jacks, eliminating the need for ballasting and avoiding waterway contamination. 

Operational cycle time is another meaningful distinction between the two approaches.

A typical lift or lower operation on the OmniLift shiplift is generally completed within one to two hours, supporting predictable berth turnover and reduced schedule sensitivity. By comparison, lift and lower operations on floating dry docks are inherently more time-intensive, often requiring several hours and, in some cases, four to fourteen hours, depending on vessel size, ballast sequencing, and environmental conditions.

These differences in cycle time can affect berth occupation, schedule resilience, and overall MRO throughput, particularly in high-tempo naval shipyards.

The OmniLift vs Graving Docks

While the OmniLift is still permanent infrastructure, it avoids the constraints of a fixed graving basin and supports more flexible, parallel workflows through onshore berthing.

From a cost perspective, constructing a new graving dock typically requires capital investment on the order of billions of dollars, driven primarily by large-scale civil works. By contrast, an OmniLift system with associated civil works is generally on the order of millions, with the majority of cost tied to site preparation and civil construction rather than the lifting equipment itself.

This difference in scale and cost structure can significantly influence how shipyards approach long-term planning, modernization, and reuse of existing infrastructure. Beyond capital considerations, however, the two approaches also differ in how they affect daily operations and maintenance tempo.

Operational tempo is another meaningful distinction between the two approaches.

Lift and lower operations for graving docks generally occur on a time scale similar to floating dry docks, with cycle times measured in many hours and closely tied to pumping, environmental conditions, and operational sequencing.

By contrast, shiplift systems such as the OmniLift operate on significantly shorter lift and lower cycles, enabling substantially higher daily throughput. In practice, some naval operators are able to perform multiple lift cycles per day, a tempo that would not be achievable with either floating dry docks or graving docks.

This difference in cycle time and repeatability can materially affect berth turnover, maintenance capacity, and overall fleet availability.

Initial Implementation Considerations

Upfront cost, site conditions, and integration with existing operations are often the primary short-term considerations.

Operational Lifecycle Implications

Over time, maintenance burden, downtime, and scheduling resilience increasingly shape total cost and effectiveness.

Flexibility for Future Fleet Evolution

Infrastructure that supports adaptability is better positioned to accommodate changing fleet requirements.

Docking decisions are fundamentally risk-management decisions. Familiar systems often feel safer because their variables are well understood, while new systems introduce uncertainty even when overall risk exposure is reduced.

Education, transparency, and operational familiarity play a critical role in technology adoption.

Effective docking infrastructure evaluations extend beyond engineering performance to encompass operational risk as a whole. These evaluations typically consider technical, human, and environmental risk alongside operational predictability and the potential impact of scheduling disruptions. Long-term cost behavior is assessed not only in terms of capital expense, but also lifecycle exposure and uncertainty over time. Equally important is alignment with dockmaster expertise and day-to-day operational responsibilities. As a result, docking infrastructure decisions are not simply engineering choices — they are operational risk decisions that shape how a yard performs under real-world conditions.

For organizations evaluating long-term shipyard infrastructure, learning more about alternative docking and transfer approaches can help determine alignment with mission requirements, risk tolerance, and operational goals.