## 3 Results and Discussion  
Duration of Hydrographic Surveys of the Same Water Area for Different Vessel Speeds and MBES Swath Angles  
In the first scenario, it was assumed that the same 10 m of depth water area is being considered, and the vessel conducts a bathymetric survey taking into account various MBES swath angles and variable speeds of movement. In order to perform the calculations, the specific parameters presented in Table 1 were adopted. In very shallow water, various opening angles of MBES can be used, most often within the range 90-150\({}^{\circ}\). With the increase in the MBES beamwidth \(\theta\), the time of surveying a water area of 5 \(\times\) 2 Nm with a water depth of 10 m decreases and ranges from almost 12 days for small angles and low speeds (for \(\theta_{u}\) = 90\({}^{\circ}\) and \(V_{pp}\) = 4 kt) to almost 1.5 days using the full capabilities of both the survey system and the vessel (for \(\theta_{u}\) = 150\({}^{\circ}\) and \(V_{pp}\) = 10 kts). \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Size of the survey area & 9260 \(\times\) 3704 m \\ Average water depth \(D\) & 10 m \\ Useful MBES swath angle \(\theta_{u}\) & 90–150\({}^{\circ}\) \\ Overlap \(p\) & 10\% \\ Length of the main survey line \(L_{pp}\) & 9260 m \\ Survey vessel speed \(V_{pp}\) & 4–10 kt \\ Time to perform vessel turns \(T_{21}\) & 300 s \\ Number of SVP measurements \(n_{sep}\) & 6 \\ Time of a single SVP measurement \(T_{sep1}\) & 600 s \\ Number of survey cross lines \(N_{PC}\) & 5 \\ vessel speed at turns to the next cross line \(V_{2 PK}\) & 8 kt \\ Time to conduct Patch test calibration \(T_{kal}\) & 2400 s \\ Number of cross-check maneuvers \(n_{cc}\) & 3 \\ Time of a single cross-check maneuver \(T_{cc1}\) & 900 s \\ Distance to survey area \(S_{rpi}\) & 3704 m \\ Vessel’s speed at the transition to the survey area \(V_{rpi}\) & 12 kt \\ Delay time due to weather conditions \(T_{up}\) & 0 s \\ Delay time due to equipment failure \(T_{ss}\) & 0 s \\ Number of detected underwater objects \(n_{ob}\) & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Hydrographic survey parameters used for calculations in scenario 1. The results of the simulation of the survey duration for the assumed operating parameters are presented in Figure 3.  
Based on the graphs (Figure 3), the selection of the appropriate swath angle of the multi-beam echosounder and the survey speed determine the time necessary to perform the hydrographic survey. For economic reason hydrographer should use the maximum MBES swath angle of 150\({}^{\circ}\) and vessel speed of 10 kts. Unfortunately, in practice, there are situations in which contractors, for economic reasons, use the maximum angle of the MBES, thus shortening the time spent in the survey area. The approach of such hydrographers approach may lead to registering the depths with errors, which might be unacceptable to the National Hydrographic Office or the customer. It is also worth adding that by increasing the swath angle of MBES, the footprint size of the outer beams increases. Thus, the spatial resolution of the echosounder decreases, which directly affects the depth measurement accuracy and detection capabilities of the system. The footprint magnitude near normal incidence (under the transducer) is relatively small; thus, the resolution is higher than for the outer beams. The hydrographer should be aware of how the resolution of the echosounder used changes as a function of the beam pointing angle. Knowing the requirements of the hydrographic survey project, it is possible to select the appropriate size of the MBES swath angle, keeping in mind the resolution parameter.