Anyone who's ever been on watch offshore knows that no human can see what a radar does. Most radars have alarms, so you know when something threatening is near. On watch you spend most of your time checking the radar and tweaking the sales.
By the way, on the Pacific Mexican coast, if you're over 100 miles offshore, there isn't likely to be anything out there. I just returned from Sicorro Island -- an active volcano that's 330 nautical miles off the Mexican Pacific mainland -- and never saw (visually or on the radar) another vessel for the first 2.5 days.