# Ship Basic Hydrostatic Parameters with definition

## 7.1.1: Hydrostatic curves

A series of graphs drawn to a vertical scale of draught and a base of length, which gives values such as the centre of buoyancy, displacement, moment causing unit trim, and centre of flotation. These curves are useful for quick assessment of the draughts and the initial stability in in various loading conditions.

## 7.1.2: Draft

The draft or draught of a ship's hull is the vertical distance between the waterline and the bottom of the hull (keel). Draft determines the minimum depth of water a ship or boat can safely navigate.

## 7.1.3: Displacement

The displacement or displacement tonnage of a ship is its weight based on the amount of water its hull displaces at varying loads. Ship displacement varies by a vessel's degree of load, from its empty weight as designed (known as "Lightweight tonnage”) to its maximum load.

## 7.1.4: Centre of Floatation

When the ship floats at a particular draft, any trimming moment acting on the ship would act about a particular point on the water plane. This point is the centroid of the area of the water plane, and is called the center of the floatation.

### 7.1.4.1: LCF:

Longitudinal center of floatation is the distance from the reference line to the center of floatation.

## 7.1.5: Center of buoyancy:

Centre of Buoyancy of a ship is defined as being at the geometric centre of the underwater volume of the ship at a particular instant and is the point through which the total buoyancy force (B) is considered to act vertically upwards.

### 7.1.5.1: LCB

This is the longitudinal centre of the underwater volume, and is the point through which all the buoyancy can be said to act vertically upwards.

### 7.1.5.2: VCB

The point at which a vertical line through the heeled centre of buoyancy crosses the line through the original one, is called vertical center of buoyancy.

## 7.1.6: Tonnes per centimetre immersion (TPC):

The amount of weight which will sink the vessel 1 cm deeper in the water, that is, the weight which will increase the draft by 1 cm is called the tonnes per centimeter immersion (TPC).

## 7.1.7: MCT 1cm

The MCT 1 cm is the moment required to change the trim of the vessel by 1 cm and may be calculated by using the formula:
MCT 1 cm = W x GML/100L.
Where, W = The vessel's displacement in tonnes.
GML = The longitudinal metacentric height in meters.

## 7.1.8: KB

The vertical distance between the keel and the center of buoyancy is expressed as 'KB'

## 7.1.9: KML

KML is the distance between keel to longitudinal metacentric height.

## 7.1.10: KMT

KMT is the distance between keel to Transverse metacentric height.

## 7.1.11: Waterplane Area

The area of a hull at a particular horizontal plane, within the waterline.

## 7.1.12: Wetted Area

The wetted area is the area of the hull (watercraft) which is immersed in water.