Strange that a guy spends so much money in tracing and old battleship just for the sheer fun of it and that he gets public recognition for this nonsense by the reputable BBC. Did he at least salvage the unexploded ammunition? But in all honesty I can't imagine he did. Why doesn't he use his money in a more meaningful way?
Maybe it's somehow not easy to be a billionaire... just imagine, everyone - including yourself - would expect you to save the planet with your millions, or billions... and if you give in to that urge, you'd be done with it in five minutes, the billions spent, the planet saved for the next five minutes, and then things would go on like nothing ever happended. So you will just keep things going, staying rich and busy, because it's too comfortable like that. And maybe you will be quite bored, though. So you are looking for some things you can do 'just because you feel like' doing them, and just because you have the cash for doing them.
Things like searching for an old shipwreck, that's anybodies childhood dream, why not?
There must be something that propelles all those billionaires to buy yachts and private jet-planes, pieces of art and exclusive real estate stuff, and even cheaper luxuries like jewelry and haute coture...
After all they might be just human and therefore so stupid like everyone else?