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.