  In this paper, we address the problem of autonomous search and vessel
detection in an unknown GNSS-denied maritime environment with fixed-wing UAVs.
The main challenge in such environments with limited localization,
communication range, and the total number of UAVs and sensors is to implement
an appropriate search strategy so that a target vessel can be detected as soon
as possible. Thus we present informed and non-informed methods used to search
the environment. The informed method relies on an obtained probabilistic map,
while the non-informed method navigates the UAVs along predefined paths
computed with respect to the environment. The vessel detection method is
trained on synthetic data collected in the simulator with data annotation
tools. Comparative experiments in simulation have shown that our combination of
sensors, search methods and a vessel detection algorithm leads to a successful
search for the target vessel in such challenging environments.
