(a) The drainage area required on a vessel must be computed using the following formula: For protected waters required drainage = .1 x Basic Drainage For partially protected waters required drainage = .5 x Basis Drainage For exposed waters required drainage = Basic Drainage where: Basic Drainage area in centimeters\2\ = 4389.12 x [(Recess Volume x Recess Ratio) + (Weather Deck Volume x Weather Deck Ratio)]; or Basic Drainage area in inch\2\ = (Recess Volume x Recess Ratio) + (Weather Deck Volume x Weather Deck Ratio) Recess Volume = (BR x DR) - VR BR = average height in centimeters (feet) of the bulwark
above the well deck or cockpit deck;DR = total deck area of the cockpit or well deck in the after
\2/3\ of the vessel length (LOD) measured in centimeters\2\
(feet\2\).VR = volume of any weather tight structure below the bulwark
of the well deck or cockpit deck. Recess Ratio = LR / LC LR = the length of the recess in the after \2/3\ vessel
length (LOD).LC=\2/3\ vessel length (LOD). Weather Deck Volume = (BD x DD) - VS BD = average height in centimeters (feet) of the bulwark
above the weather deck;DD = total deck area of the weather deck adjacent to bulwarks
but not in way of the cockpit or well deck in the after \2/3\
of the vessel length (LOD) measured in centimenters\2\
(feet\2\).VS = volume of any weather tight superstructure below the
bulwark on the weather deck located within DD. Weather Deck Ratio = LD / LC LD = the length of the weather deck bulwark in the after \2/
3\ of the vessel length (LOD).LC=\2/3\ vessel length (LOD).
(b) Vessels with bulwarks in the forward part of the vessel shall not form a well with the deckhouse which retains water. [CGD 85-080, 61 FR 966, Jan. 10, 1996; 61 FR 20557, May 7, 1996]