I've melted moist or wet wheelweights before, just dump them all in the big pot (cold pot!!!) turn on the propane turkey frier, and it all steams away long before the lead begins to melt. The big no no is to add wet material to already melted lead.
You can pour a cup of water into your lead melt and all you will get is angry steam. Drop the cup of water into the mix so it goes under the surface and you will have a nice steam powered molten lead grenade!
Now, barnacles are new to me... I'll take your word on dealing with them.