## 3 Data Collection  
To predict the propulsion power, a 200,000-ton bulk cargo ship was chosen. The general arrangement of our target vessel is shown in Figure 1. Also, the detailed specification is depicted in Table 1. The target ship is dedicated to iron ore transportation and operates only on two regular routes: from South Korea to the US and from South Korea to Australia. Since it operates on a small number of stable routes, the data quality was thought to be reliable. For the propulsion system of the target ship, a fixed-pitch propeller whose pitch angle cannot be changed is adopted. Figure 1: General arrangement of the vessel. The detailed description of the dataset is shown in Table 2. Most of the data were collected using sensors installed onboard the vessel. The target feature to predict is shaft horsepower which indicates the amount of mechanical power that is delivered by the engine to the propeller shaft. For the input features, velocity, draft, rotation per minute of shaft (RPM), sea depth, tide, wave height, and wind vectors are chosen. Sensor information of each data feature is also illustrated in the same table. The collected data were then processed through the Voyage Data Recorder (VDR) system which digitizes, compress and stores the information in an externally mounted protective unit. Under regulations of the IMO (International Maritime Organization), a cargo ship that weighs more than 20,000 tons should be equipped with VDR. Although the primary purpose of the VDR is to assist marine causality investigation, the recorded data also can be used for performance monitoring of the vessel. The picture of the VDR system installed on the vessel is shown in Figure 2. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Specification** & \\ \hline Length Overall & 269.36 m \\ Length betw. perpendiculars & 259.00 m \\ & Breadth & 43.00 m \\ & Depth & 23.80 m \\ & Draught & 17.3 m \\ & Deadweight & 152.517 metric t \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specification of the target vessel. \begin{table}
\begin{tabular}{c c c c} \hline \hline  
In processing the raw data obtained from different sensors, many computational steps would be required. For example, the shaft horsepower can be measured with the torque which can be measured with strain. The loading torque \(T\) is calculated by the following:  
\[T\ =\ \frac{\varepsilon\pi GD^{3}}{8} \tag{6}\]  
where \(\varepsilon\) is shaft strain, G is shaft material shear modulus (pa) and D is shaft diameter (m). To accurately measure the torque, a strain gauge is attached to the propeller shaft of the vessel. The strain gauge measures the change in electrical resistance of the shaft and converts it into the torque. Several commercial system providers [22; 23] as well as software vendors [24] are available for shaft power measurement. For our target ship, the SpecsVision-TPM system [25] is used for measuring and processing the shaft power. In addition to the shaft power measure, the raw data collected from the different sensors were processed by the data acquisition unit (DAU) of the VDR system. DAU transforms each sensor data according to the industrial standard protocol and synthesizes the data from different sensors into a structured data table wherein each datum is recorded at the same time periods. As a result, the synthesized data are transmitted throughout the satellite-based communication system and stored into the cloud database. As a result, each data observation is generated every 10 s, and overall 178,000 observations were collected over seven months (from 2016.01 to 2016.07). The data protocol information used to process the sensor data is also shown in Table 2.  
To collect the wave height, which cannot be measured directly on board the vessel, the National Oceanic and Atmospheric Administration (NOAA) database is utilized. NOAA collects spectral wave data using accelerometers on board the buoys which measure the heave acceleration of the buoy. A fast Fourier transform is then applied to obtain the wave height.