Grounding plates in your boat size are mostly for lightning.
The DC grounds through the engine/prop shaft.
All 8 of your stays/shrouds, the 7 bronze thru hulls, the engine, and the mast are all bonded together. The wires are visible on all except the mast, where there is a wire-attached metal plate under the base.
With your internal ballast, you can't exit lightning through the keel as there are no bolts. Bristol exits the lightning through the shaft and 7 thru hulls. It also keeps the rig at the same electrical potential as the ocean.