A New and Accurate System for Measuring Cruising Yacht Freeboards With Magnetostrictive Sensors

Knowing the freeboard levels of a yacht is crucial for boat builders and hull designers because it allows them to easily obtain precise information about the ship displacement, as well as about its trim. This paper describes a system that automatically performs the freeboard acquisition (substituting the rudimental and inaccurate manual reading currently used) with a great improvement of the measurement automation and accuracy. It consists of a wireless sensor network, the nodes of which are three magnetostrictive water level sensors, an inclinometer, and a personal-computer-based central unit. The major error sources in the measurements have been investigated and controlled to be below a desired accuracy by compensating for temperature and water-density variations. In fact, one node of the network is equipped with an additional level meter that allows the direct and automatic measurement of the water density, i.e., a fundamental parameter to calculate the boat displacement. The experimental results show the functionality of the system and also its great potential in extracting additional information for yacht characterization by means of postprocessing the acquired data.