Ships are typically optimized at the design stage for a specific speed and draft. This optimized condition may not always be the actual operating condition. At other combinations of draft and speed the trim can often be changed to reduce the fuel consumption.

The hull resistance is influenced by the trim of the vessel through:

• Viscous resistance: linked to the wetted hull surface, which will differ slightly as the vessel changes trim

• Wave making resistance: linked to the wave pattern. Waves carry energy, i.e. larger waves imply more fuel spent.

The effect of trim on fuel consumption can be measured at the model scale in a towing tank, or simulated at full scale using Computational Fluid Dynamics (CFD). Many different speed and draft combinations can be simulated accurately in a time efficient manner with a fully viscous flow description (Reynolds Averaged Navier Stokes Equations –RANS).

Our CFD analysis can predict accurately both the wave making resistance and the viscous resistance around the vessel. Subtle differences in wave pattern can be captured. The result of our CFD analysis is a set of hull resistance curves which can be used to identify the optimal trim settings for a given loading condition and speed. Each trim is compared to a reference case, in order to highlight the favorable trims and those to preferably avoid. Trim optimization studies are not limited to new ship designs. They can easily be performed for existing ships.

DNV can optionally deliver an on-board visualization tool to assist the crew in finding the best trim for any combination of draft and speed.

DNV Trim Optimization service:

• Clear result presentation
• Fit for on-board use
• The only success is implementation!