What Ship GA (General Arrangement) Plan Depicts?


GA plan depicts the division and arrangement of the ship:
  • Side View.
  • Plan Views of most important Decks.
  • Cross-sections.
The views and sections display: 
  • Division into compartments (tanks, engine room, holds)
  • Location of bulkheads
  • Location and arrangement of superstructure
  • Parts of the equipment (winches, loading gear, bow thruster, life boats).
Basic data included in the GA Plan:
  •  Dimensions (Length, Breadth, Draft)
  • Volumes of the holds (Cargo Capacity Grain & Bale)
  • Tonnage
  • Deadweight
  • Engine power
  • Speed (Service Speed)
  • Class

Important Decisions for Planning of General Arrangement Drawing

For general arrangement drawing some important decision is to be determined about
1. Trim
2. Location of Machinery Space
3. Storage of Liquid
4. Cargo Holds
5. Hatchways
6. Accommodation/Superstructure Arrangement

6.3.1: Trim

A level keel trim is usually specified for the full load condition with homogeneous cargo. This is mainly to make the best use of the available depth of the water in port usually a restrictive item.

6.3.2: Location of the Machinery Space

A major decision is to determine the position of the machinery space. In a light condition the density of the machinery space and the accommodation, taken together, is greater than the rest of the ship’s length. In a loaded condition the reverse is truer. This is important when considering trim.

6.3.3: Storage of Liquid

One the size and position of the machinery space has been decided then attention can be turned to rank spaces. Normally these are confined to double bottoms but deep tanks may be arranged for additional water ballast in the fore and aster peaks for trim or near amidships to control hull girder bending. Fuel reserve storage may be arranged at the double bottom, but there should have a service/ ready use (RU) tank for continuous consumption. Few other tanks are required for storing dirty/contaminated oil, gray water or black water as per new IMO conventions.

6.3.4: Cargo Holds

The number of holds is dictated largely by the size of the ship and the type of cargo. Requirements, which came into force in February 1994 for the damage stability and survivability of cargo ships, have brought flooding into consideration.
Holds in container ships will have lengths which are multiples of the container length (plus an allowance for the cell guides). A hold around 40 ft long can take either one 40 ft container or two 20 ft containers; a hold 60 feet long can take 3 at 20 ft or two at 30 ft or one at 40 ft and one at 20 ft depending on how the cell guides are set up.
In dry bulk carriers the usual of number of holds is a choice from 5, 7 or 9. Five holds are common in Handy Size vessels of around 25,000 tonnes deadweight; seven holds are the usual choice for a 75,000 tonnes deadweight Panamax vesssel; while nine holds are often found in the largest Capsize vessels of 150,000 tonnes and over.
The height from the double bottom to the upper deck will be divided by tween decks in accordance with the requirements of the trade. Thus none will be found in Bulk Carriers while Fruit Carriers and Banana Carriers will have the total depth of the hold divided into tween decks. The height of the tween deck may vary between 2.4m and 3.0m. The clear height in the hold varies immensely but it should be noted that some cargoes will crush if loaded too deeply.

6.3.5: Hatchway

Hatchway is a means of passing through a wall or floor, having a hatch (especially on a ship); a doorway with a hatch rather than a door. Large hatchway assists easy cargo working but hatch widths are restricted by the need to maintain not only the cross sectional area of deck material for structure reasons but also the shelf space at the tween deck levels. The ingenious use of twin hatches, side by side, can facilitate both good cargo working and the constrained by the length of deck taken up by cargo gear and hatch cover stowage.

6.3.6: Accommodation/Superstructure Arrangement

Usually the accommodation in a material ship is sited above the machinery space and around the engine casing to minimize interference with cargo operations. The result is a short, high superstructure giving good forward visibility but possibly compromising stability. A good arrangement is large a matter of common sense, experience and foresight. 
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