The safety of fishermen in small fishing vessels is of continuing concern as there are many reports of fishing vessel -ship collisions along the Western coast of India. These accidents are mainly caused due to the over reliance on the radar systems which fail to detect small boats or due to the negligence from the side of the shipping crew. This paper proposes the architecture of an affordable warning system that can be implemented onboard the fishing vessels to warn the vessel crew about the approaching vessels. This system exploits the principle of underwater passive acoustics for designing a more reliable and user friendly system based on hydrophones for localizing the nearby vessels. A novel algorithm based on time difference of arrival and law of cosines which resolves the quadrant error and quadratic root ambiguity is discussed in this paper. The simulation result of the algorithm is also presented.
