I'm going to chime in here......thanks everyone!

Since this thread was started, an old time shipwreck treasure hunter has contacted me, we exchanged a lot of emails. He and his partner over the years, dove on more than 100 shipwrecks. Like Mel Fisher eventually did, they believe in all methods of treasure hunting.
It also to me was so, very interesting to hear about all the gold finds. Once they began to try dowsing, gold finds were common and the process obviously is very awkward (holding the rods level while over the dive hatch). To dowse Au hits, it started near shore then going out, away from a known shipwreck. I've now looked over a few of these dowsed charts, lines with arrows fanning out from shore.
On one stretch of a wreck alone, they picked up nearly 50 gold coins from a gold rush era site, all in nearly or maybe all were in perfect uncirculated condition. The miners would have raw gold minted into gold coins, very common back then. Sometimes a gold hit turned out to be only a 14K gold scribe pen, another time a gold/emerald ring.
Anyway, these guys are funded (I believe) by the gold finds rather than investor money. Shipwreck salvage is so expensive, either you get investor money poured in or you make enough good Au dowsing finds, otherwise your treasure hunting business is going to sink. Soon one of these gold finds (being held) will have to be sold, to pay for a new boat motor. Being funded by gold finds, you have no big investor payout to soak up the money.
So, how did they learn? Answer is from another old time shipwreck treasure hunter no longer around (has long since passed away). No, gold finds won't make you a billionaire, even in shipwreck salvage.