# An Integrated Safety Monitoring and Pre-Warning System for Fishing Vessels
## 3 Materials and Methods
### Decision Support Subsystem
#### 3.5.2 Vessel Attitude Anomaly Assessment Method  
Heaving, rolling, and pitching are the most critical parameters for describing the vessel's attitude [35; 36; 37; 38], which are combined to forecast the fishing vessel's navigation safety. However, it is important to note that the sensor installed onboard does not measure  
Figure 6: Control software interface.  
heavy motion directly. Instead, the heave acceleration is measured, and from these data, the vessel's heave motion can be inferred.  
The heave acceleration is a key metric in assessing the vessel's stability and sea-keeping performance. In the fuzzy logic control model, the heave motion limits are defined in terms of acceleration, rather than displacement, as the installed nine-axis sensor (JY901) measures acceleration along with the roll and pitch angles. The heave acceleration limit is set at a roll of 20\({}^{\circ}\), a pitch of 10\({}^{\circ}\), and a heave acceleration of 0.65 g, which are the maximum values for safe navigation, as referenced from previous studies on vessel safety performance [39, 40].  
Additionally, the fuzzy logic control method is used in this study because it is robust and reasonably easy to construct, as it does not need knowledge of the precise models. The fuzzy logic system presented in this study has three input variables (heave acceleration, roll angle, and pitch angle) and one output variable (predicted danger score).  
Vessel heave acceleration, H, is divided into five fuzzy subsets from 0 to 0.69 g as (heave negative big (HNB), heave negative small (HNS), heave zero (HZR), heave positive small (HPS), heave positive big (HPB)), as listed in Table 3.  
Similarly, vessel roll angle, R, is divided into five fuzzy subsets from 0\({}^{\circ}\) to 20\({}^{\circ}\) as [roll negative big (RNB), roll negative small (RNS), roll zero (RZR), roll positive small (RPS), roll positive big (RPB)], as listed in Table 3.  
Vessel pitch angle, P, is divided into five fuzzy subsets from 0\({}^{\circ}\) to 10\({}^{\circ}\) as [pitch negative big (PNB), pitch negative small (PNS), pitch zero (PZR), pitch positive small (PPS), pitch positive big (PPB)], as listed in Table 3.  
Vessel dangerous score S is an output of the fuzzy controller, for which the quantification domain is [dangerous negative big (SNB), dangerous negative small (SNS), dangerous zero (SZR), dangerous positive small (SPS), dangerous positive big (SFB)].  
The derivation of the fuzzy control rules is based on Table 3, and five examples of these criteria (a total of \(5\times 5\times 5\) = 125 rules) are shown in the table.  
Figure 7 depicts a fuzzy decision surface that demonstrates the link between input (H, R) and output (S) using the fuzzy control rules when pitch P is constant. It can be found that if H is very high and R is very large, S will be very high. This indicates that a hazardous scenario for vessel securing could result from the combination of strong roll and big pitch motions.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{H\({}_{\text{NB}}\)} & \multicolumn{4}{c}{H\({}_{\text{NS}}\)} & \multicolumn{4}{c}{H\({}_{\text{ZR}}\)} \\ \hline \multirow{2}{*}{R} & P & & & & & & & & & & & & & & & & \\ \cline{2-16}  & P\({}_{\text{NB}}\) & P\({}_