2132. In illustration D033DG below, what is the strake of shell plating indicated by letter H known as?

Letter H indicates the first strake of bottom shell plating adjacent to the keel, which is the garboard strake. This strake is located at the bottom of the hull, directly alongside the keel, distinguishing it from the bilge strake (at the bottom's curve), the sheer strake (at the deck edge), and the keel plate itself.