This paper presents an image-processing-based fuzzy auto-
pilot scheme for accomplishing small-boat approaching
maneuvers in a harbor environment. In the proposed approach,
two canvas targets are arranged in cascade on the quayside to
form a leading line. The targets are detected by a charge
coupled device (CCD) camera mounted on the bow of the boat,
and their geometric centers are computed by a Hue- and
Saturation-based image-processing scheme. The autopilot
system calculates the current heading deviation and tracking
deviation angles of the boat by analyzing the displacements of
the target centers relative to the CCD center line. These angles
are then supplied to a fuzzy-logic-based control system to
determine the rudder commands required to bring the boat
back on course. During the approaching maneuver, the auto-
pilot system estimates the distance between the boat and the
quayside using a simple trigonometric relationship, and at a
certain pre-defined distance, automatically switches the steer-
ing control system from an approach mode to a berthing
control mode. The experimental results obtained using a small
FRP boat confirm the ability of the autopilot system to
accomplish the approaching maneuver and show that the
estimated value of the boat-to-quayside distance deviates by
approximately 10~20% from the exact value.