Page 27 - Introduction to Naval Architecture

DEFINITION AND REGULATION 15

watertight volume of ship above the waterline. That is a minimum
freeboard to provide a reserve of buoyancy when a ship moves through
waves, to ensure an adequate range of stability and enough bouyancy
following damage to keep the ship afloat long enough for people to get
off.
Freeboard is measured downwards from the freeboard deck which is the
uppermost complete deck exposed to the weather and sea, the deck
and the hull below it having permanent means of watertight closure. A
lower deck than this can be used as the freeboard deck provided it is
permanent and continuous fore and aft and athwartships. A basic
freeboard is given in the Load Line Regulations, the value depending
upon ship length and whether it carries liquid cargoes only in bulk.
This basic freeboard has to be modified for the block coefficient,
length to depth ratio, the sheer of the freeboard deck and the extent of
superstructure. The reader should consult the latest regulations for the
details for allocating freeboard. They are to be found in the Merchant
Shipping (Load Line) Rules.
When all corrections have been made to the basic freeboard the
figure arrived at is termed the Summer freeboard. This distance is
measured down from a line denoting the top of the freeboard deck at
side and a second line is painted on the side with its top edge passing
through the centre of a circle, Figure 2.5.
To allow for different water densities and the severity of conditions
likely to be met in different seasons and areas of the world, a series of
extra lines are painted on the ship's side. Relative to the Summer

Figure 2,5 Load line markings