The name describes it well. For most of the time it can be a lightweight boarding plank, but on those unfortunate occasions when someone falls in, it can be immediately turned into a rescue ladder. (It is also useful for access when blacking the boat, too)
The total weight is only 10kg, which is lighter than the average wooden plank.
The ladder-plank folds up when not in use and stands on its own four feet so you don't need to use pole and plank holders. Click icon below picture to see ladder folded.
The standard ladder-planks are just under 6 feet long and the ladder part is 15" wide with a steadying support 25" wide on one end. The alternative longer ladder-plank is just under 8 feet long, but otherwise the same.
Maximum safe weight on either ladder is 16 stone (100kg) when extended.