Before a vessel enters service, engineers rely on a range of modelling and testing techniques to estimate how efficiently it will perform. These approaches help designers optimise hull forms, propulsion systems and other technical elements that influence fuel consumption. In this insight, we examine the main design-stage tools used to assess ship performance and consider why their results do not always reflect real-world operating conditions.
Various methods are applied to develop and validate ship designs before they enter service. The aim is to simulate and refine the vessel’s performance under idealised, controlled conditions. These methods include numerical calculations, such as computational fluid dynamics (CFD), model tank tests, and sea trials.
CFD allows engineers to isolate and test specific hydrodynamic or design variables in a controlled, repeatable digital environment. Because of this control, CFD is valuable in early-stage design and retrofit validation, helping shipowners predict relative changes before investing in physical modifications.
The accuracy of CFD models depends on various factors including the calibration of turbulence and flow parameters, the quality and representativeness of input data, and the use of appropriate extrapolation methods from model scale to full scale.
One limitation of CFD analysis is that designs are often evaluated at just a single operational point. This is typically the ship’s contract speed, which is usually defined at around 80–85% of MCR. In practice, however, vessels operate across a wide range of speeds and drafts.
For example, a large container ship may sail anywhere between 12 and 20 knots and at drafts between 12 and 17 metres. When performance is assessed only at one condition, say 20 knots at full design draft, the predictions may not reflect how the vessel behaves across its true operating profile.
Model tank tests provide another method for assessing performance. These tests are performed in calm, measurable conditions that remove environmental noise such as wind and current. They give tangible, observable results that provide benchmark data for validating numerical methods such as CFD.
However, tank tests fail to capture fouling or weather variations of real operations. In addition, the sides and base of the tank reflect and change the waves, meaning the water around the model doesn’t behave the same way it would in open sea.
Sea trials provide full-scale measurements and are often used to establish speed-power curves and propulsion benchmarks. Yet even these rely on calm seas, a clean hull, and deep water, conditions that are not always representative of real operations.
Because each method has limitations, reliable performance assessment requires combining CFD simulations, tank tests, and sea trials. When these methods are cross validated and linked with real operational data collected during service, they provide a stronger benchmark for evaluating vessel efficiency.
Download ‘The 5-10% Illusion’ and explore why the maritime industry’s reliance on unverified efficiency claims is eroding trust, and discover a framework to restore measurement discipline.
