Dynamic Positioning vs. thruster-assisted mooring: a comparative assessment of efficiency and cost

A recent evaluation examined the operational efficiency of a Mobile Offshore Drilling Unit (MODU) using a thruster‑assisted mooring system versus a standalone dynamic positioning (DP) system in deepwater conditions. The study focused on three key metrics: fuel consumption, CO₂ emissions, and overall cost impact.

Methodology

To capture realistic offshore conditions, the analysis applied 12 selected Beaufort sea states, with wave height, period, and current speed scaled using environment exceedance charts. Each condition was assessed across 24 vessel headings, resulting in 168 load cases for each station-keeping option.

Thruster performance was calculated for every scenario and mapped against regional wind‑rose data to estimate station-keeping power demand. This enabled accurate projections of fuel use, CO₂ output, and related costs for all environmental conditions. The study incorporated contemporary market rates, including fuel pricing, mooring line rental, MODU day rates, and anchor‑handling vessel (AHV) support.

The comparison highlights several compelling advantages of incorporating a mooring system:

• Reduced Thruster Demand

  Mooring support decreased thruster utilisation by approximately 21.5%, directly lowering fuel burn and associated emissions.
   

• Potential to Optimise MODU Class Requirements

  By lowering overall DP capability requirements, the moored arrangement may enable operators to consider a MODU or vessel of reduced class rating. Given the significant influence of MODU and vessel hire rates on campaign budgets, this presents a meaningful cost‑saving opportunity.
   

• Improved Fuel and Cost Efficiency Over Time

  In this evaluation, the moored configuration became more cost-efficient than the DP only option after 57 days, driven primarily by reduced fuel consumption and the ability to use a lower-class MODU, which decreases charter costs

Overall, the assessment showed a 9.5% reduction in total campaign cost when adopting a smaller class MODU with a thruster assisted mooring system over a standalone DP solution.