Sequence of Keel and Frame Construction

Once the keel is in place it is checked for dimensions and for level, as this structure will now be used as the reference point for all other measurements.

After the keel has been trued up, the yard will start to attach frames to it. The frames will usually be made of the same kind of metal as the keel (in this example, steel). The frames will usually be made of angle bar, T-bar, or I-beam to provide strength and an attachment surface for other structures such as decks or bulkheads. The frames will be formed in presses or rolled lengthwise to achieve the desired shape along the side of the ship. On large vessels the frames will be made up in multiple lengths and the pieces will be welded end- to-end until the desired shape is achieved.

With modern equipment, the shapes can be determined utilizing computer assisted machines, but in early times, each frame was drawn out in an area of the shipyard called 'the loft'. Patterns (molds) could then be made and the raw steel manipulated until it fit perfectly along the desired lines. With computers, the forming machines will form or "bump" the steel over heavy dies until the shape is achieved. With laser monitoring available today, the results are precise.

After the keel is in place and the frames attached, the decks, bulkheads tanks and the other internal structures will be constructed. This phase of construction can include heavy structural door frames, steel pipe used to support decks, and extra heavy plates under winches, windlasses and mooring gear.

Workers then utilize the ships drawings to begin fabricating and assembling machinery supports for such things as boilers or diesel engines that will be strategically placed and welded to the frames. For strength as the build progresses, the frames will be joined together horizontally with long sections called longitudinals. These pieces are similar to the frames, but lay on their sides, and are strategically placed to provide support when the outside hull/shell plate is welded into place.

The perimeter bulkheads that enclose the various machinery spaces, fuel tanks, water tanks, and sewage tanks will start to be fabricated onboard as work continues. Many of these structures will have brackets attached and holes for pipes and electrical work. Various deck levels will start to take shape inside the vessel with the large heavy plates and other materials dropped down by a crane, or winched in through the side of the vessel. Any heavy reinforcement for such things as sea water inlets, rudders, steering posts, and anchor points will be located and welded into place. Ideally all the heavy "pieces" will be put into place with crane support before the areas become congested with piping, wiring and electrical cabling.

After the engines, pumps, and other heavy equipment have been installed at each level, the ship can start to be "closed up". The outer skin of the vessel referred to as the hull plate or shell plate will be fitted and welded onto the frames. The fit between the shell plates must be done with precision to ensure the welds are of a high quality. Too much gap and the plates won't be properly attached. Too tight and the welding wire or welding rods will not fully penetrate the plate and there will be voids within the welds that could fail. On many ships, sections of the hull will actually be X-rayed at strategic points to ensure the plate is assembled and welded correctly. To achieve a good weld, the edges of the plate where they butt into each other are chamfered at a set angle (depending on the thickness) and then multiple passes of weld will be used to seal up this intentionally made valley, inside and out. During this welding stage, the shell plate will be affixed to the frames of the vessel as the workers make their way along the side.

Sections of the upper deck may also be welded on, but the final fit will usually be left until the end in case any trimming needs to be done. Upon completion of this work, the shipyard will install the outer deck "houses" and all the equipment found on the outside of a ship. Compared to modular or block construction, the keel and frame construction can be heavy and dangerous with many overhead lifts, but it is a tried and proven way to build even the heaviest of ocean-going vessels. The process is still used today by many yards around the world.