The risk of terrorist attack on large cryogenic hydrocarbon fuel tankers is unclear, due partly to difficulties in understanding how the spill, pool vaporization, turbulent dispersion and fuel-vapor mixing are coupled. The current study's objective is to model the vaporization, dispersion, and deflagration of liquid methane pools boiling on water while subjected to airflow around a prismatic body. The Fire Dynamics Simulator CFD code developed by NIST facilitates large-eddy simulations of the turbulent dispersion that is coupled to a combustion model capturing premixed flame ignition, propagation, and if sustainable, transition to diffusion pool fire. The pool and water are characterized as isothermal surfaces with a dominant convection heat transfer mode. Flammable mass, cloud visualization, flame height, temperature, and heat flux provide diagnostics. Slower winds produce larger flammable clouds, but insufficient mixing inhibits successful ignition. Provisional adjustment of the flammability limits demonstrates reasonable flame height and diffusion flame heat release rates.