Modular or Block Construction

Block Construction

Most modern shipyards now build vessels indoors in large modules or blocks as opposed to laying down a keel, erecting frames and then plating everything in steel or aluminum out in the drydock. Block construction is done for many reasons including ease of construction, safety, space considerations, protection from weather, and increased quality control on paints, coatings and internal equipment. Depending on size, a ship can be built in any number of blocks, and in large vessels, the size of the blocks can be huge. If the blocks contain tanks or open cargo areas they are as wide as a large freighter, and can be up to 100 feet long. If a particular block contains huge diesel engines or large generators they can weigh 100 of tons and be several stories high.

Construction Sequence

Although the construction sequence can vary what follows is a typical sequence of construction starting aft end and working forward:

      1. The first block: containing the rudder and steering gear assembly;
      2. The second block: the main engine;
      3. The third block: a machinery space with auxiliary equipment such as HVAC, blackwater and various pumps;
      4. The fourth block: storage or habitability areas, and
      5. The fifth or foremost block: the bow, chain locker and mooring equipment affixed to it.
      6. The deckhouses and the superstructure could be fitted on top as the vessel takes shape.

Depending on how much space the shipyard has, it is important to sequence these huge modules so that they can be welded together sequentially thereby preventing unnecessary handling and storage, usually outside in the weather. The other interesting factor in building this way is that the blocks are built upside down. All the electrical lines, piping and even the deckhead insulation can be installed when the block is flat on the ground, thus eliminating ladders, lifts or other potentially dangerous working situations.

Designing Block Construction

The large "blocks" that comprise modern ships are built upside down and are completed with as much equipment and finished surfaces as possible. Interior bulkheads can be sandblasted and painted, with piping, insulation, and even doors installed prior to being fitted to the next block or module. All that is needed is for the workers to leave sandblasted boundary areas for the hull 'blocks' to be welded together and proper amounts of excess pipe and cabling so that connections can be made, and systems joined between the blocks. Engineers design and draw the electrical runs and piping systems to join up exactly. Measurements of the various deck must be done with care as the blocks will be welded together and where these decks join, there are often doorways or bulkheads that must be welded into place.  Many of these are prefabricated to fit in exactly one location. Exact design is made possible by specialized computer programs. Much of the machinery in the shops is also computer driven and enables hundreds of pieces to be made with very specific tolerances; also known as repeatability.

There are examples when ships have been in collisions and software is used to replicate the damaged sections, which are then replaced with a high degree of accuracy.

Modular or block is now used by shipyards throughout the world because of its many advantages:

Short build times

Typically 30-50% less time than traditional on-site construction (depending on the class of ship being constructed)

Superior quality

Achieved by factory-based quality control. Also most construction is done indoors or under hugh shelters so that construction is unaffected by adverse weather conditions.

Economy of scale

Repetition of prefabricated units leads to considerable economy of scale in production. Multiple pieces can be built concurrently, even in different or remote areas and welded together because they are not waiting for support beams, frames or decks to be erected.

Environmentally less sensitive

Efficient factory production techniques are less wasteful and installation is less disruptive on site. There is also the ability to contain dust and fugitive emissions that would otherwise escape into the atmosphere if the ship was con-structed outside.

Safer construction

Modular construction can reduce workplace risk by reducing the need for ladders and scaffolds. Modular construction also provides large open spaces so that more than one or two workers can be gainfully employed in a particular space or area; thereby shaving time from the overall schedule.

Reduced professional fees

Standardized design details reduce the need for specialist design input.

Find out more about how block construction was used to build the Hobart Class destroyers.