Jacob's ladder (nautical)
The term Jacob's ladder,[1] used on a ship, applies to two kinds of ladders.
The first is a flexible hanging ladder. It consists of vertical ropes or chains supporting horizontal wooden or metal rungs. Today it is used mostly to allow people to board a ship from small boats, hence it is better known as a Pilot ladder. Because the decks of most commercial ships are far above the waterline, pilots and others who need to come aboard at sea can only do so if a Jacob's ladder is put out. When not being used, the ladder is stowed away (usually rolled up) rather than left hanging. On late 19th-century warships this kind of ladder would replace the normal fixed ladders on deck during battle. These and railings would be removed and replaced with Jacob's Ladders and ropes while preparing for battle the days before. This was done to prevent them from blocking line of sight or turning into shrapnel when hit by enemy shells.
The second applies to a kind of ladder found on square rigged ships. To climb above the lower mast to the topmast and above, sailors must get around the top, a platform projecting from the mast. Although on many ships the only way round was the overhanging futtock shrouds, modern-day tall ships often provide an easier vertical ladder from the ratlines as well. This is the Jacob's ladder.