## 4 Results and Discussion
More precisely, it surpasses the conversion efficiency of the encoding using CSV text with tags by 69.6%, the fixed-length CSV text encoding by 36.0%, the fixed-length binary encoding by 33.3%, and the differential CSV text encoding by 9.4%. In addition, the required computation time of the compression procedure is shown in Table 5 for each tested algorithm. These values represent the average processing times required to compress the data corresponding to one second to be transmitted, and the processing time value is shown in seconds. The computation times were obtained as a result of processing by a C language program in a Windows 10 OS environment on a PC equipped with an Intel(r) Core(tm) i7 Processor. Using the proposed algorithm, the data required to be transmitted in one second is compressed in 0.000253 s. Therefore, it can be said that the computation time for the compression using the proposed method is almost negligible. Moreover, as seen in Table 5, the computation time required by the proposed data compression algorithm is significantly lower than those required by the other tested methods. Figure 16 shows the visual comparison of the tested onboard data encoding methods regarding the required transmission rates during the 22 days considered. The transmission rates are given as percentages of the reference transmission rate required to transmit data in the original format. As seen in Figure 16, the proposed method provides stable performance throughout the observed period, with a conversion efficiency superior to the other tested methods. It is assumed that the compressed data will be transmitted using, for example, the data line of Immarsat satellite communication. As shown in Table 4, as a result of compression, the speed required for data communication is about 1 kbps, and it can be said that it is realistic to use a data line of satellite communication. The experimental results shown in Table 5 and Figure 15 are averaged using the data acquired in various situations, and it is unlikely that the compression ratio will change significantly depending on the nature of \begin{table}
\begin{tabular}{c c c c c c} \hline  & **CSV Text** & **Fixed-Length** & **Fixed-Length** & **Differential** & **Differential** \\  & **with Tags** & **CSV Text** & **Binary** & **CSV Text** & **Binary** \\ \hline
**Average** & 73.0\% & 39.4\% & 36.7\% & 12.8\% & 3.4\% \\
**St. dev.** & 7.5\% & 4.4\% & 5.4\% & 1.6\% & 0.4\% \\
**Comp. time** & 0.001324 s & 0.001320 s & 0.000379 s & 0.000537 s & 0.000253 s \\ \hline \end{tabular}
\end{table} 
Table 5: Required transmission rates achieved by the tested shipboard data conversion methods and the corresponding compression times. The transmission rates are given as percentages of the transmission rate required to transmit data in the original NMEA sentence format. The required computation times are given in seconds. the data. Therefore, the proposed encoding algorithm should always be selected, and it can be said that the reliability of communication depends on the communication line used. The data used was obtained sailing in the western part of Japan and near Kyushu Island. The ship's route is shown in Figure 17.  
Figure 16: Comparison of the shipboard data conversion methods in terms of the required transmission rates relative to that required to transmit data in the original NMEA sentence format. Figure 17: Route of TS _Fukae Maru_ during the data acquisition.