380	NICHOLLS'S   SEAMANSHIP  AND   NAUTICAL   KNOWLEDGE
These additional lines are indicated in Figure 19. They are marked
on the ship's side abaft the centre of the disc, the seasonal lines being
preceded by the letter L but, otherwise, they have the same significance

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LAVN

I	I
Fig. 19 —Load Lines for Timber Cargoes.
as the ordinary load lines forward of the disc. It will be noted that the
freeboard for a ship when timber laden is less than for other cargoes.
The freeboard for summer draught is deduced from the Timber
Load Line Tables for any particular ship and this fixes the position of
the L S mark.
L W is £ inch per foot of L S draught lower than L S.
L T  is J inch per foot of L S draught higher than L S.
L W N A is at the same level as W N A.
LOAD LINES FOR TANKERS.
A "tanker" includes all steamships specially constructed for the
carriage of liquid cargoes in bulk, and a series of rules regulates the
minimum freeboard assigned to this particular type of ship.
They have load line marks similar to other steam vessels, but the
W N A mark is 1 inch per 100 feet in length of ship lower than
the winter mark.
Full information with the modifications applicable to ships which
differ in length, sheer, ratio of superstructures to length, etc., from the
basic ship on which the Tables are founded is given in the "International
Convention respecting Load Lines," price 3s., H.M. Stationery Office,
ZONES AND SEASONAL AREAS.
The various oceans and seas have been divided into "Summer,
Winter and Tropical Zones" having definite geographical boundaries;