# Measurements of High-Froude Number Boat Wakes near a Seawall
## 2 Materials and Methods
### Sensor Array  
Four RBR Coda 3 pressure gauges were mounted on a 2 m \(\times\) 2 m square transportable platform, along with an RBR Concerto 3 data logger (Figure 3) that synchronized and recorded all measurements. The sensors were set to measure pressure \(p_{i}(t)\) (sensor number i), at a sampling frequency \(f_{s}\) = 4 Hz, sufficient to sample most surface gravity waves. The array frame was constructed from 1\" diameter PVC piping. The mean water depth at the sensor site was about 1.2 m. The array was deployed about 62 m offshore from the seawall.  
The dimension of 2 m was selected to provide a phase difference of the measured waves across the array. Typical wave periods in Tampa Bay are about 2 s [50]. Site inspection prior to gauge deployment found this value to be a nominal lower bound to the wave period. The wavelength of these fast waves can be estimated using the deep water approximation \(\lambda=T^{2}\sqrt{2\pi/g}\), about 3 m. The 4 Hz sampling rate of the array therefore yielded about 7 points per cycle. Larger waves with longer periods had more points per cycle. Longer periods would have larger wavelengths until they transition to intermediate or shallow water conditions, where \(\lambda=T\sqrt{gd}\), and increasing sample points per cycle.  
During deployment, the array was fixed about 2 cm off the bottom using screw mounts to secure their position. Changes in water level induced by waves induced changes in bottom pressure, which were measured by the sensors. The sensors selected for this project had an accuracy \(\leq 3\times 10^{-4}\) dbar, or around 0.3 mm, and were factory-calibrated. There was no method to compensate for variations in the bottom terrain (nominally 1-10 cm). These small variations only impacted the absolute depths, not measures of the tidal and wave signals that were the focus of this study. The gauge and logger were activated before they were deployed and were stopped when they were disassembled after recovery and cleaning. Pressure data for all sensors were downloaded using the RBR Ruskin v2.19.1 software package. The deployment examined here was from 22 November 2022 to 21 December 2022.  
Figure 1: Location of the wave gauge (star). (**a**) Tampa Bay major segments and location on the Florida coast (inset). NOAA gauge 8726607 location (green). (**b**) Navigation chart near deployment. Depth units are feet.  
Recreational boats that compromised almost all the traffic in Safety Harbor do not broadcast through the Automatic Identification System [38], so their size, position, and velocity could not be determined. Therefore, ten controlled boat passes were performed over a period of one hour, and their resulting wakes were measured by the array. On 29 November 2022, personnel from Pinellas County made 10 boat passes in the vicinity of the wave gauge (Table 1). Three position readings were taken during each pass along with the boat speed. The boat was a Parker XL1800 (Cleveland, OH, USA), 5.2 m long, with a 115 HP motor. Pass 'A' in Table 1 was a skiff driven by a private citizen of indeterminate length. No other boats were operating in Safety Harbor in the vicinity of the gauge during this time. Wind speeds, as measured by a NOAA gauge located about 18 km from the study site, the day before and during this exercise were \(<\)4 m/s (Figure 2), so wind-waves  
Figure 3: Schematic of sensor array. Numbered sensors are red, and the logger is blue. Geographic orientation during deployment is indicated.  
Figure 2: Hourly winds from NOAA gauge 8726607 in Old Tampa Bay (Figure 1). (**a**) wind speed (blue) and mean scalar speed (black); (**b**) wind direction (degrees True).  
were weak compared to the boat generated waves. This was not always true during the entire deployment.