Computer vision: object detection with labels that are single coordinates
The state of the art in such problems is done these days via deep neural networks. Among others, two popular and recent approaches for solving the problem of detection and localization of objects are the YOLO paper, and the faster-RCNN, which run a classifier over many variously sized regions in an image.  

As humans, boats and cars are popular object classes, I'd first attempt to see what existing pre-trained networks can do for your problem, and then, if needed, try and re-train them using your data.