Virtual testbed is a computer programme that simulates ocean waves, ship motions and compartment flooding. One feature of this programme is that it visualises physical phenomena frame by frame as the simulation progresses. The aim of the studies reported here was to assess how much performance can be gained using graphical accelerators compared to ordinary processors when repeating the same computations in a loop. We rewrote programme’s hot spots in OpenCL to able to execute them on a graphical accelerator and benchmarked their performance with a number of real-world ship models. The analysis of the results showed that data copying in and out of accelerator’s main memory has major impact on performance when done in a loop, and the best performance is achieved when copying in and out is done outside the loop (when data copying inside the loop involves accelerator’s main memory only). This result comes in line with how distributed computations are performed on a set of cluster nodes, and suggests using similar approaches for single heterogeneous node with a graphical accelerator.