(a) The drainage area required on a vessel must be computed using the following formula:
For protected waters required drainage = .1 × Basic Drainage
For partially protected waters required drainage = .5 × Basis Drainage
For exposed waters required drainage = Basic Drainage
where:
Basic Drainage area in centimeters2 = 4389.12 × [(Recess Volume × Recess Ratio) + (Weather Deck Volume × Weather Deck Ratio)]; or
Basic Drainage area in inch2 = (Recess Volume × Recess Ratio) + (Weather Deck Volume × Weather Deck Ratio)
Recess Volume = (BR × 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 centimeters2 (feet2).
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 × 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 centimenters2 (feet2).
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]