Difference Between Bulkhead and Bulwark

A bulkhead is a vertical partition that divides a ship's internal spaces, mostly within the hull. A bulwark is a wall along the edge of the open deck. The bulkhead divides the ship into compartments and keeps flooding and fire contained; the bulwark stops people and cargo going over the side. Both are vertical steel plating and the words sound alike, which is why they get mixed up, but they do different jobs in different places.

What a bulkhead is

Bulkheads are the vertical partitions that divide the inside of the ship. Transverse bulkheads run across the ship from side to side; longitudinal bulkheads run fore and aft, as between a tanker's cargo tanks. With the decks, they split the hull into separate compartments: the cargo holds, the tanks, the engine room and the peaks at each end. Superstructures and deckhouses have bulkheads too, forming their outer walls and the partitions in the accommodation.

Bulkheads do three jobs. Watertight bulkheads limit flooding to the damaged compartments if the hull is breached, so the ship can stay afloat; SOLAS and classification rules decide how many there are and where they go. Bulkheads built and insulated as fire divisions slow the spread of fire and smoke between spaces, particularly around the accommodation and the machinery spaces. And transverse bulkheads stiffen the hull against the loads from the cargo, the sea and the ship's own weight.

The collision bulkhead is the first watertight bulkhead from the bow. SOLAS sets both a minimum and a maximum distance for it from the forward perpendicular: at least 5 per cent of the ship's length or 10 metres, whichever is less, and not more than 8 per cent of the length or 5 per cent plus 3 metres, whichever is greater.

It must be watertight up to the bulkhead or freeboard deck, so that a ship holed in a head-on collision floods only the fore peak. Below that deck it may have no doors, manholes, access openings, ventilation ducts or other openings, except a single pipe for the fore peak tank fitted with a valve that can be worked from above the deck. Elsewhere, openings in watertight bulkheads are kept to a minimum and closed by watertight doors.

The Titanic is the best-known case of subdivision that did not go high enough. Her watertight bulkheads did not extend to a high enough deck, and as the bow went down, water spilled over the top of one bulkhead into the next compartment. The first SOLAS convention was adopted in 1914 in response to the disaster, although the First World War prevented it from coming into force.

For the different kinds in more detail, see types of bulkhead in shipping.

What a bulwark is

A bulwark is steel plating that continues the line of the ship's side above the weather deck, topped with a rail and supported by stays. The Load Line Convention requires bulwarks or guard rails at least 1 metre high on exposed decks, with a lower height allowed where 1 metre would interfere with the ship's operation and protection is otherwise adequate. Because a bulwark can trap water on deck, it must have freeing ports at deck level that let shipped seas drain overboard.

A bulwark protects the crew on deck, keeps deck cargo and gear on board, and reduces spray over the deck edge. It is not part of the watertight hull and is not designed to carry the hull's main bending loads.

Bulkhead and bulwark side by side

Where you can see each one

Bulwarks are visible from the quayside along the deck edge of many cargo ships, often with mooring fairleads set into them at the bow and stern. Most bulkheads are seen only from inside the ship: the steel walls between the holds, the forward and after boundaries of the engine room, and the partitions in the accommodation. The front of a superstructure, seen from the deck, is a bulkhead too.

For the decks that both structures meet, see ship decks and their purpose.