This work is focused on the interactive navigation through highly polygon-populated ship environments. A conservative visibility algorithm is presented that hierarchically computes visibility for different observer positions and stores it in a new octree based structure, the Visibility Octree (VO) The VO is used during the navigation. Its main contribution is the ability to provide an effective control over the coarseness of the visibility approximation. Some results are presented for indoor ship scenes that show that the VO is efficient on densely occluded scenes.