A new general-purpose three-dimensional underwater acoustic ray-tracing program called HARPO is demonstrated by simulating acoustic measurements in the Florida Straits. We illustrate how important it is to avoid adding unrealistic features when modeling the medium by showing that slope discontinuities in the bottom yield fictitious jumps in raypath properties as launch angle varies. Starting with simple models of sound speed and bathymetry (topography of the bottom) and Eater adding complexity increases insight into the relation between the medium and the propagation. The simple models we used provide a generic picture of propagation over the Miami Terrace, which can be used in experiment design and to assess the effects of perturbations in the sound speed and bathymetry. Our range versus launch-angle plots give information about relative signal strength due to ray spreading. Our range versus travel-time plots provide arrival time pulse sequences for all ranges of interest in a single plot. Because small details in the bathymetry have only a small effect on the range versus travel-time plots, our results for a simple bathymetry model give a reasonable estimate of the pulse arrival times for realistic bathymetry. Range versus launch-angle plots, on the other hand, are very sensitive to the details of the bathymetry. The insensitivity of pulse strength (through ray spreading) to details of the bathymetry suggest a measuring strategy in which pulse arrival time provide a measurement of sound speed and pulse strength provides details of the bathymetry.