Topic-1 MAIN DIMENSIONS

Basic design of the Ship

The main dimensions of the barge influence many of the ship’s characteristics such as stability, carrying capacity, power requirements and its economic efficiency. So, they should be coordinated such that the vessel satisfies the design conditions as well as the characteristics desired by the shipping companies with various combinations of dimensions. The owner requires a vessel which will give him the best possible returns for his initial investment and operating costs. Basic design includes selection of main dimensions, hull form, power, and type of generator, preliminary arrangement of tanks and machinery, and major structural arrangements. Proper selections assure the attainment of the mission requirements such as carrying capacity and deadweight. It includes checks and modifications for achievement of required carrying capacity, subdivision of tanks and stability standards, freeboard and tonnage measurement. 

    Length (L)

The length of the ship is measured from the extreme forward end to the aftermost point of the stern. The length, L, shall be taken as 96 percent of the total length, in meters (feet), on a waterline at 85 percent of the least molded depth, D. In barges designed with a rake of keel, the waterline on which this length is measured shall be parallel to the designed waterline.

 Breadth (B)

The breadth of a ship is its width at the widest point as measured at the ship's nominal waterline. It is measured in meters.

    Depth (D)

Depth is defined as the height of the ship at the midship section from the base line to the molded line of the deck at side.

      Draught (T)

The draught of a ship's hull is the vertical distance between the waterline and the bottom of the hull (keel), with the thickness of the hull included. Draught determines the minimum depth of water a ship or boat can safely navigate. The draught, T, is the molded draught, in meters (feet), from the molded baseline to the summer load line.

SHIPBOARD MEASUREMENTS

A ship’s size and capacity can be described in two ways--linear dimensions or tonnages. Each is completely different yet interrelated.

A ship’s measurement is expressed in feet and inches--linear dimensions. A ship is a three dimensional structure having length, width, and depth.

A Ship’s Dimensions

Draft - The depth of a ship in the water. This vertical distance is measured from the bottom of the ship to the surface of the water. Draft marks are cut into or welded on the surface of a ship’s plating. They are placed forward and aft on both sides of the hull and also amidships. At the midships draft we will also find the authorized Load Line markings which designate maximum drafts allowed for vessels under various conditions.

Freeboard - The vertical distance from the water line to the top of the weather deck on the side.

FREEBOARD

Freeboard is the distance between the waterline and the freeboard deck at mid length. The freeboard deck is the uppermost continuous deck which has means of closing all openings. Rules allow different freeboards for different ships in relation to their construction and cargo they carry. There are two types of ship;

Type A -which covers vessels designed to carry only liquid cargoes.

Type B-Which covers all other types of ship,

For type A ships cargo tanks must only have small openings which can be effectively sealed

Type B ships must have sufficient bulkheads and sealing arrangements for openings, but such openings e.g. hatches can be large

The freeboard allowed will be smaller for the type A ship compared to the type B ship of similar length because of the type of cargo carried and means of access for water. Type B ships classed as B-60 may have their freeboard reduced by 60% of that required for a normal B-100 ship provided that its method of construction approaches that of the type A ship. This type exists with OBO's.