Gridirons are an early form of tidal shiplift. A series of timber baulks is set in the intertidal range. At high tide a boat (or rarely a ship) is floated onto the gridiron. As the tide falls, the boat settles onto the gridiron. At low tide the boat is accessible for inspection, hull scraping etc.
Media in category "Gridirons (tidal)"
The following 6 files are in this category, out of 6 total.