### Motivation and Main Contributions  
Shore-to-ship communication studies in the literature are comparatively summarized in terms of the models and carrier frequencies used in the studies, as shown in Table 1. When shore-to-ship communication-specific measurement and modeling studies in the existing literature were examined, it was observed that free space (in [2; 9; 12; 13; 14; 15; 20]), log-distance (in [11; 12]), simple 2-ray (in [8; 12; 13; 15; 17; 18; 21]), 3-ray (in [14]), 2-ray + additional parameters (REL) (in [1; 3; 9; 19; 20]), ITU-R (in [1; 3; 16; 20]), Karasawa (in [16]), COST231 and Okumura-Hata models (in [2]) were used. However, the publications [1; 2; 9; 13; 17; 21] were performed for different carrier frequencies than the 5.6 GHz band, which is within the scope of our study. On the other hand, [14; 15] recommended the piecewise model approach and proposed 2-ray+3-ray and 2-segmented 2-ray models, respectively. In our study, experimental measurements were performed for four different environmental scenarios at 5.6 GHz carrier frequency for shore-to-ship communication, and the fit of the models used in the literature to the data was examined. Their performances were compared, and a path-loss model called Modified REL was developed. Subsequently, a Proposed Piecewise model, which uses the Modified REL and Log-distance models together, was developed by proposing a piecewise modeling approach for the data. The motivation of this proposal is to reduce the fitting errors between the measured data and the REL model, which shows a better fit than other models by considering the nature of the shore-to-ship propagation environments and providing a more generalizable modeling approach. The main contributions of our work can be summarized as follows:  
* A Modified REL model that represents environmental factors more flexibly and provides higher accuracy in shore-to-ship communication scenarios was proposed by considering the estimated \(h_{rbest}\) and the varying paths and gains of the direct and reflected waves as additional parameters for each scenario unlike in the traditional REL model. * A piecewise modeling approach based on dividing the propagation environment into two different regions based on the \(d_{break}\) distance (calculated from the Fresnel zone theory) and modeling each region with appropriate models (Modified REL and log-distance) was proposed. This approach shows higher accuracy compared to the use of a single model. * Comprehensive experimental data were collected at 5.6 GHz for four different shore-to-ship communication scenarios along the Black Sea coast in Trabzon, Turkiye. * The proposed models were comprehensively evaluated in terms of fit to the experimental measurement data and compared with existing models in terms of fit performance (free space, log-distance, dual-slope, 2-ray, 3-ray, and REL). * The Modified REL and proposed piecewise approach presented lower error rates (RMSE) and higher model fit (R\({}^{2}\)) than existing models, providing more reliable and accurate predictions for shore-to-ship communication. During the measurements, the Tx vehicle was parked on the shore, while the Rx boat moved away from the shore until communication was lost, and tried to return to the shore again following the same route. Throughout the experiment, the measurement data from both the Tx and Rx MK5 OBU devices were recorded on an SD card. These measurement data include the GPS location of the vehicle and the boat with the values of some parameters, such as the received signal strength, heading, and speed. The 5.6 GHz frequency band was selected for shore-to-ship measurements to comply with the Regulation on Short Range Radio Devices published by the Turkish Information Technologies and Communication Authority. Four separate shore-to-ship measurements were carried out on different days. During the measurements, the Tx vehicle was kept stationary on the shore, while the Rx boat moved away until communication was interrupted and returned to the shore by following the same route.