General arrangement

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General Arrangement

The General Arrangement, or GA as it is commonly called, is a drawing created by a naval architect. The purpose of this drawing is for space allocation, to ensure that everything that an owner wants in a vessel will actually fit. The GA consists of (at a minimum) a plan view of each major deck of the vessel, shows all of the watertight and structural bulkheads, as well as joiner bulkheads. All of the furniture is typically shown or in early stages the furniture and large items to be on the vessel are roughly blocked in (though this may be broke out into arrangement drawings for complex arrangements). Passageways, stairwells and all equipment vital to the ships operation are shown. The ship spaces (head, mess, etc.) are shown.

Contents

Arrangement

The general arrangement has, at a minimum, plan views of the major decks. Other decks, such as tank tops, exterior flats, elevated platforms, or raised enclosures will be shown on more advanced/detailed GA's. Additionally;

Outboard Profile

A view showing only the externally visible features of the vessel. The outboard profile is important in conveying not only aesthetic features of the vessel, but the general geometry of deckhouses & superstructures. The outboard profile also provides some indication of deck and equipment heights. The outboard profile will also list the principal particulars.

Inboard Profile

The inboard profile shows a cut-away view through the centreline of the vessel, inclusive of centreline structures. Early on, the inboard profile will show little more than bulkheads, however it is a useful drawing for determining stairway runs, fire zones, trunks, and understanding tank arrangements if not accompanied by a tank plan.

External Views

End views are often added, particularly where a vessel has bow or stern operated equipment. Top views are occasionally seen, particularly on vessels with complex towing arrangements, or extensive exterior deck spaces. Bottom views are rarely used unless the vessel has a complex or unique propulsion arrangement.

3D Views

With the rise of 3D modelling and development software, bow & stern quarter views can be generated within a reasonable time frame. They are beneficial in conveying the overall concept of the vessel and are increasingly being seen.

Development

Concept Design

With project development, the general arrangement takes on increasing complexity (see design spiral). In concept design, a GA not based on a parent design will generally only show bulkheads, tank boundaries, and space allocations. Allowances will be made for engine arrangements, however selected engines or even engine types may not be shown. Stairwells are blocked out, though deck heights may not yet be frozen so stair lengths may only be indicative. Focus is on the mission specific equipment and overall philosophy.

Preliminary Design

Initial developments of shafting arrangement, structural arrangement, and specification dictate many of the features included in the preliminary GA. This drawing will include frame spaces, all major service trunks, hatches, escape routes, soft patches, masts, major equipment, major items, lifeboats, rafts, work boats, cargo handling systems, structural allowances, etc.

Contract Design

The contract design GA is the fully detailed final product. Additional to the preliminary GA, joiner bulkheads, liners, insulation, accommodations arrangements, windows, portlights, scuttles, minor equipment, electronics, gratings, anchors & ground tackle, railings, stanchions, closing fixtures, louvres, door types (weathertight, watertight, fire), structural profiles, bitts, cleats, chocks, appendages, etc. will be shown. Additionally, these will show all final selected equipment.

As-Built

The as-built drawings are developed from the contract design GA, with additional changes to match minor changes as occur during the construction of the vessel. These changes are often maintained in a manner in which they can be distinguished from the underlying GA, such that the changes are evident.

In-Service

Over time, vessels typically experience refit or equipment changes which may be reflected on a "living" or in-service GA.

The GA as a Design Document

The general arrangement is the first drawing typically created. The GA will be under constant development as a project progresses, constantly dictating design direction to sub-systems of the vessel and then integrating the details of these systems as they are properly developed. All designers should be checking their design choices against the GA to help prevent conflicts. That said, conflicts are inevitable and often solved at the general arrangement level. It is therefore important that the general arrangement be constantly updated to keep pace with development of the vessels systems and dependent arrangements.

Conflict Resolution

Conflicts are inevitable with most ship-sized design projects. Typically, they can be resolved by some rearrangement of the vessel or change in its general capacity. The overall effectiveness of a design will be measured by how well the compromise between systems have been solved. Two major considerations to keep in mind when resolving any conflict are the ship's primary function, and the requirements of the regulatory framework in which it must meet.

Arrangement Considerations

Some considerations for arrangement drawings;

  • Major equipment should be placed first with due regard to their operation
  • Major design requirements, such as capacities, should be then arranged
  • At all stages, placement of all items on the GA should give consideration to the anticipated structural arrangement - i.e., bulkheads should be placed on framespaces (or anticipated framespaces), open areas should anticipate pillaring, higher deck heights should be specified where deck loads will be high (to allow for structure), etc.
  • Clashing items should be segregated early: i.e., passenger/crew separations, living spaces away from sources of heat, vibration and noise.
  • Functional spaces should be grouped logically and in proximity to each other. Traffic flows to be considered.
  • Sanitary spaces should be aligned for ease of pipe runs, and with regard to maintenance access.
  • Weight distribution & sources of heeling moments should be carefully considered with due consideration to the vessels stability.
  • Emergency exit paths: Escape routes should be redundant, simple, increase in capacity towards the muster station or boat deck, minimize panic, prevent bottlenecking, and avoid likely sources of danger. Small design decisions (such as the swing direction of a door) can have fatal results.
  • Functional allowances: How are supplies moved onboard, and around the vessel? Room may have to be left for the movement of palletted stores, overhead chain blocks may be needed in machinery spaces for the movement of spares, equipment removal patches may have to be incorporated, lift systems may be required to move heavy items between decks.
  • Crews tend to spend extensive amounts of time at sea. The level of accommodation & comfort must have high standards.
  • Cultural sensitivity: The designer should be sensitive to the beliefs of the people who will operate the vessel. A bar, for example, may be a necessity or an insult.
  • Tradition - deck names, locations of equipment, relative sizes of rooms, etc. may have traditional dictates which experienced crews will expect to be met. For example, the master is typically housed on the port side of the vessel; the chief engineer opposingly to starboard.

Regulatory Bodies

In addition to class, flag state, owner & IMO requirements, there may additionally be labour requirements (by guild or union) which will dictate the acceptability of a given design. Meeting all requirements can impose major restrictions on a vessel and it's arrangement, inclusive of deck sizes, number of heads/showers/sinks, crewing levels, bunking arrangements, passageway sizes & numbers, numbers and dispositions of doors, segregated spaces, etc.

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