Here is a wooden "Gang Plank" that I built for my dogs to board our boat. It measures 36"x18". The green parachute chords are used to secure the plank to the boat's rails, and I placed three "non-slip safety steps" on the top for my dogs . The noodle on the bottom is to protect the boat's gelcoat from the 1"x2". The plank is only 1/4" plywood, so I do not recommend stepping on the plank.
