378 NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE
Details of Marking.—Figure 17 indicates the relative positions and
the lengths of the lines, the diameter of the disc and the method of
determining the level of the top edge of the deck line. The disc, lines
and letters are to be painted in white or yellow on a dark ground or in
black on a light ground. They are also to be carefully cut in or centre
punched on the sides of iron or steel ships, and on wood ships they are
to be cut into the planking for at least one-eighth of an inch. The
marks are to be plainly visible, and, if necessary, special arrangements
are to be made for this purpose. All lines are 1 inch in breadth and the
top edge of the respective lines limits the ship's immersion in different
.circumstances and in different seasons.
Actual Freeboard is the distance between the upper edge of the
deck line and the waterline.
Statutory Freeboard is the distance between the upper edge of the
deck line and the upper edges of the respective load lines.
The Summer Load Line is indicated by the upper edge of the line
which passes through the centre of the disc and also by a line marked S.
Its position is deduced from the Load Line Tables for any particular
ship.
The Winter Load Line is indicated by the upper edge of a line marked
W. It is \ inch per foot of summer draught lower than S.
The Winter North Atlantic Load Line is indicated by the upper edge
of a line marked W N A and is 2 inches lower than W. It applies to
vessels less than 330 feet in length trading across the North Atlantic
north of latitude 36° N.
The Tropical Load Line is indicated by the upper edge of a line
marked T. It is J inch per foot of summer draught higher than S.
The Fresh Water Load Line is indicated by the upper edge of a line
marked F~
The difference between S and F is the allowance to be made in fresh
water at the other load lines*
The Tropical Fresh Water Load Line is indicated by the upper edge
of a line marked T F. The distance S 'to F=T to T F.
The difference between the minimum freeboard in fresh water of
unit density and the minimum freeboard in salt water is determined
by the formula: Difiplacement~-4:OXtona per inch immersion, tne
displacement and the tons per inch being for the summer