Due to increasing terrorist threats and illegal proliferation of nuclear material and technology, there is a need for increased research in the area of detection of smuggled fissile material, some of which is designated by the International Atomic Energy Agency as special fissile material. This thesis focuses on a hypothetical scenario in which a terrorist organization has managed to smuggle an amount of special fissile material onto a personal recreational watercraft and sail it into a marina. If the boat could be forced to go through a detector system, then the contents could be interrogated and a determination made of whether any special fissile material was aboard. This thesis examines the hypothesis that active interrogation may be used successfully in the detection of special fissile material in such an environment. It shows that it is feasible to use an active neutron system to detect a significant quantity of special fissile material onboard a small boat via the differential dieaway technique. The MCNP Monte Carlo transport code was used to simulate the use of a pulsed neutron generator to induce fission in the fissile material and then estimate the detector response. The detector modeled was based on elastic scattering-induced recoil protons using pure hydrogen gas. There was a significant difference between the system with and without the presence of fissile material, and the estimated detector response for the system with fissile material present was shown to be sufficiently greater than the response due to background radiation only. Additionally, dose was estimated and found to be small enough that the system would not likely pose a significant radiological health risk to passengers on the boat.