Beer can tied to a rope, hmmmm, I seem to recall that hi-tech device being in my boat and it worked very well. Knots were tied every two feet in the rope, dropped over the side to determine depth or hung over the bow at a certain depth to follow contours. The luxury models could locate brush piles and other under water structure.
The only real draw back was not being able to use the device at high speeds which didn't matter anyway, cause I never could get that dam row boat, up on plane.
Weather looking good for tomorrow Ops, get out there and get em.
Tight lines.