## 4 Results and Discussion  
The performance of the proposed shipboard data compression method has been experimentally tested on the data collected on board TS _Fukae Maru_. The data were collected during the ship's voyage in 2019. The recorded data cover 22 days, and the measurements were taken 24 h a day. In this experiment of applying the proposed differential binary encoding technique, all data items were also transmitted once every minute to ensure all information is received regardless of when the reception started. Figure 14 shows an example of the shipboard data collected during a random time of 1 s. The data are transmitted in their original format based on the NMEA sentences. As shown in Figure 10, this format requires a total of 75 lines to represent this particular 1 s of data. On the other hand, Figure 15 shows an example of the onboard data encoded using the proposed six-bit differential binary encoding scheme. As shown in Figure 15, the same data as in Figure 14 can be represented with only 11 lines instead of 75 lines, using the proposed encoding technique. Moreover, the next 3 s of data are encoded using only 2, 3, and 2 lines of code, respectively. The significant reduction in the number of data lines required is achieved by encoding and transmitting only data items that have changed their values. As shown in Figure 15, when sending the compression result, the two-digit hexadecimal number following \"\" is added as a checksum at the end of each line. This checksum is calculated in the same manner as the checksum field of the NMEA-0183, enabling error detection. By doing this, the code can detect errors. Table 4 provides values for the size of the shipboard data collected during each day of the ship's voyage and for the corresponding transmission rates required to transmit those data. The data collected over 22 days add up to 8 277 905 025 bytes when transmitted and recorded using the NMEA sentence standard in the form of the ASCII text. On average, 376 268 410 bytes of data are collected per day with a standard deviation (st. dev.) of 57 362 724 bytes, requiring an average data transmission rate of 34 840 bps with a standard deviation of 5 311 bps. The maximum transmission rate required was recorded on day 14 and was 46 097 bps, whereas the minimum required transmission rate of 28 316 bps was recorded on day 19. Figure 13: Flowchart of the proposed shipboard data encoding method. The standard deviation of the transmission rates for this method is 159 bps (0.4%). The maximum absolute value of the required transmission rate was recorded on day 14 and was 1 564 bps (3.4%), whereas the minimum value, recorded on day 4, was 926 bps (3.0%). Regarding the relative percentage values of the required transmission rate, the maximum value of 4.1% (1 199 bps) was recorded on day 21, while the recorded data shows the minimum value of 2.5% (1 066 bps) occurred on day 15. Table 5 provides the quantitative comparison of the proposed variable-record-length six-bit differential binary encoding method with several other data conversion methods of similar complexity, considering both fixed-record-length and variable-record-length methods. The tested methods include data encoding using Comma Separated Values (CSV) text with tags indicating the data items, encoding based on fixed-length simple CSV text for all data items, fixed-length binary encoding, and variable-record-length method based on differential data encoding in the form of text values with tags. The comparison is made based on the data transmission rates required after the application of each method to the actual shipboard data, thus providing information on its conversion efficiency. The transmission rates are expressed as percentages of the transmission rate required to transmit data in the original NMEA sentence format. The results presented in Table 5 show that the proposed encoding method outperforms other techniques tested.