svbeatrix.com — The website of the Sailing Vessel Beatrix, Kelly-Peterson 44 #276 (1980).
The sea hood (often called a "turtle") keeps seawater from washing over the forward companionway hatch into the cockpit. This design does not screw onto the deck, but instead sits on wooden rails attached to the hatch support and acts as a "hat" so that water runs off before it can get to the top of the hatch. A neoprene rubber seal runs around the edge where it attaches to the splashboard. The sea hood is held in place by wood screws that go through the splashboard and by 2 wood screws on each side. For a detailed drawing download the plans here.