Try using the search function. 30-50, 150-160, 450-470, 480-485 and 850-870mhz. Marine traffic will be in the 156 - 158. Find the most active frequencies write them down and then use the Uniden Sentinel 100 & 200 SW to program in the scanner.
Look at the antennas on the cars. The smaller the antenna the higher the frequency.
Be careful someone might not like you listening!!