I did this for a while (6 mos?) and got pretty discouraged. Seems any wreck that is yielding is usually already claimed and trespassing is illegal. Finding new wrecks takes years and years and years as well as millions of dollars.
Most successful treasure hunters are backed by investors to the tune of millions of $$ to pay for all the expenses.
I, too, spent some time using my underwater detector and found tons of nails, old ship part, bottle caps and other trash... ha ha
It was kind of fun, until I realized it was just another expensive hobby (and I had enough of those already).
BUT... it does provide a good form of recreation, thinking and fun if you are into it. My problem was that I was more into finding valuables than the act of poking around with a metal detector.