D-Mod Hydroplane Racing

While on my walk this morning I noticed a stack of boats with the words "D-Mod Hydroplane Racing" on the side at the corner of Farmgate and Westgate. Wikipedia remarks these boats are also known as thunderboats. Hydroplane Boat and Race Museum (sound warning). Fun. D-Mod seems to be a category of engines, with the modified bit indicating customizations over stock. I think. I'm a newbie.