I. Introduction
In-service continuous ultrasonic thickness monitoring of ship hulls, conducted in the pulse-echo mode from inside the ships, has the potential to reduce maintenance and service costs. This technique can also help to mitigate significant inaccuracy in estimating wall thickness associated with surface corrosion while the ship is in service, provided that the cost of instrumentation and transducers is low enough for their permanent installation in situ, and the recorded echo waveforms can be interpreted online.