Copper plate found on hull...

Hello All! Took boat out in the river, put on scuba gear and dove to scrub hull and put new shaft zinc on. Found a thick copper plate on stbd side. 3/4 inches thich, 14 inches long, 4 inches wide, pointed on forward end, flat on the aft end. So, I reckon it's a grounding plate for SSB or to ground against lightning?? Can anyone tell me how it is connected? I'm thinking to the lead in the keel and then via the stainless keel bolts? Very interesting... Have never seen any copper strap or braid anywhere in bilge, but wasn't really looking. Thanks for any help/advice. You guys are the most knowledgable! Kevin