The flow over a finite-height cylinder of height/diameter ratio of 1, with one end mounted on a ground plane, and the other end free, is studied experimentally and numerically. The context of the work is the investigation of numerical simulation methods for marine hydrodynamics, the aims being to test various simulation methods on a complex three-dimensional separated flow. The experiments add to the sparse knowledge of this flow, particularly through the particle velocimetry (PIV) measurements which provide more detailed measurements of the flow. The surface flow visualisation images illustrate many features of the flow. Other measurements taken include hot-wire anemometry of the velocity fluctuations in the wake, surface pressure measurements, and force measurements. A logical progression through different simulation techniques has been followed, starting with a basic Reynolds-Averaged Navier-Stokes (RANS) solution of the flow, using the k-ε model, which gave a poor prediction of the flow. Large-eddy simulations (LES) were performed which give better agreement with the experiments but fail in the modelling of the boundary layer flow on the ground plane. The next step was a detached-eddy (DES) simulation, which is hybrid RANS/LES model. This gives a better prediction of the flow near the wall, while retaining the benefits of an LES simulation away from the wall. These are believed to be the first LES and DES simulations of this flow. In the context of marine hydrodynamics, which typically involves high Reynolds number flows, the DES methodology appears to offer a promising way forward. Particular attention has been focused on the flow around a typical tanker hullform where the flow in the propeller plane is highly turbulent. It is proposed that DES would be useful in this situation to obtain information about the turbulent flow here. The synthesis of experiments and simulations has shed new light on some of the key flow features around the truncated cylinder. In particular the horseshoe vortex system has been shown to consist of four vortices although they are not all visible in some experimental measurements. The flow over the free-end which was the subject of some debate has been shown to consist of a single vortex arching over the free-end rising from two swirl patterns on the surface. The wake is seen to consist of chaotic eddies with no dominant shedding frequency.