## 3 Hydrodynamic Characterization of Designed Hulls  
Hydrodynamic characterization is one of the most critical topics in marine structures for understanding the performance of a designed model. Hydrodynamic performance can be divided into resistance and propulsion, seakeeping and ship vibrations, and maneuvering. The measurement of hydrodynamic performance can be classified into three approaches: an empirical/statistical approach, a numerical approach (CFD based), and an experimental approach (scaled model test and full-scale trial). In this section, landmark research on sensor applications for characterizing the hydrodynamic performances of marine structures is comprehensively reviewed. [PERSON] and [PERSON] [70] conducted lab-based resistance measurement of passenger ship models using different bows to verify the capability of the computational result. Three bulb-shape models were tested in the towing tank, where five resistance-type wave probes were mounted on the beam at five locations. The resistance was measured together with the dynamic sinkage and trim of the free-towed model. In 2011, the effect of heave and pitch motions on resistance and the ice-breaking pattern was investigated by [PERSON] and [PERSON] [71]. The towing mode test in an ice-going tanker ice basin was idealized as a spring-mass system, with a load cell as the spring element and a ship model and its mass as the mass element. Several sensors were used to measure the response. A pointer in the carriage was used to measure the broken channel, and a dynamic motion unit (DMU) at the bow measured the heave and pitch accelerations. Moreover, two cameras using the coordinate system were used to measure the cusp width. In the following year, [PERSON] et al. [72] conducted research on the hydrodynamic design and performance of an underwater hull-cleaning robot. Several sensors and instruments were mounted on the HCR's body to measure the hydrodynamic performance on the towing tank. A resistance dynamometer with a capacity of 3000 N was mounted to measure the drag force. The HCR's horizontal speed was measured using an electromagnetic flowmeter, and a commercial weighing scale was used to measure vertical thrust. The following year, in a collaboration project between IIHR and CNR-INSEAN, [PERSON] et al. [73] proposed a comprehensive experiment to investigate the seakeeping behavior of Delft 372 fast catamaran advancing in head waves. The catamaran model was towed through a kinematic system at the CNR-INSEAN water tank. Each demi-hull of the catamaran was connected by a transversal aluminum beam to ensure free pitch motion and restrain surge, sway, and roll movements. The position and motion of the model were identified using a Krypton optical system with three infrared LEDs. Two transducers (a Kenek probe and a Keyence ultrasound wave probe) fixed to the carriage measured the incident wave system. For wave elevation measurement, a second wave system (set of two probes) was mounted aside the hull at the LCG position. Two HYDRONICS load cells mounted between the gimbal and the model were used to measure the total resistance directly in waves. A data acquisition system with a sample rate of 300 Hz was used to record all of the physical quantities. [PERSON] et al. [74] performed an experimental investigation in a water tunnel to measure frictional resistance reduction. Skin friction reduction using air lubrication techniques generated on the hull's lower surface at various flow rates was observed. In this work, different flow rates were controlled by a flow meter. Images captured the air layer types, and two floating-plate-type friction sensors were used to measure local friction changes. [PERSON] et al. [75], under the Lecco Innovation Hub project, reported a full-scale measurement using the 10-m Sailing Yacht Lab obtained during the first sea trials carried out in offshore Colico Marina. A description of the scientific framework, measurement capabilities, and data acquisition procedure is provided.