Nice tutorial.
I don't get it why some people are unhappy with not-perfect sonar, that's part of the game right? Just imagine how much more challenging the game would be if they modeled shoals of fish (common), wrecks, sea states, and weather/temperature conditions, and the very common problem of water being disturbed by DCs and making regaining contact on the very next pass nearly impossible. Now, that would be a hard game.