The term Jacob's ladder, used on a ship, applies to two kinds of ladder. The first is a flexible hanging ladder which can be lowered down the side of a large ship. It consists of vertical ropes or chains supporting horizontal wooden or metal rungs, and is used to allow people to board the ship from small boats. 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.
The second kind of Jacob's ladder is found on some square rigged ships. To climb above the lower mast to the topmast and above, sailors must get round 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.
