Certain vessels are assigned Timber Freeboards but before these can be assigned certain additional conditions have to be met. One of these conditions is that the vessel must have a forecastle of at least 0.07 the length of the vessel and of not less than standard height, which is 1.8 metres for a vessel 75 metres or less in length and 2.3 metres for a vessel 125 metres or more in length with intermediate heights for intermediate lengths. A poop or raised quarter deck is also required if the length is less than 100 metres. The letter L prefixes the load line marks to indicate a timber load line.[8] Except for the Timber Winter North Atlantic freeboard the other freeboards are less than the standard freeboards. This allows these ships to carry additional timber as deck cargo, but with the facility to jettison this cargo.
The letters on the Timber Load line marks have the following meanings:
LTF – Timber Tropical Fresh Water
LF – Timber Fresh Water
LT – Timber Tropical Seawater
LS – Timber Summer Seawater
LW – Timber Winter Seawater
LWNA –Timber Winter North Atlantic
The Summer Timber load line is arrived at from the appropriate tables in the Load Line Rules.[9]
The Winter Timber load line is one thirty-sixth of the Summer Timber load draft below the Summer Timber load line.
The Tropical Timber load line is one forty-eighth of the Summer Timber load draft above the Summer timber load line.
The Timber Fresh and the Tropical Timber Fresh load lines are calculated in a similar way to the Fresh Water and Tropical Fresh water load lines except that the displacement used in the formula is that of the vessel at her Summer Timber load draft. If this cannot be ascertained then these marks will be one forty-eighth of the Timber Summer draft above the Timber Summer and Timber Tropical marks respectively.[8]
The Timber Winter North Atlantic load line is at the same level as the Winter North Atlantic load line