(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 × Basic Drainage
For exposed waters required drainage = Basic Drainage
where:
Basic Drainage area in centimeters
2 = 4389.12 × [(Recess Volume × Recess Ratio) + (Weather Deck Volume × Weather Deck Ratio)]; or
Basic Drainage area in inch
2 = (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 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 × 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 span 966, Jan. 10, 1996; 61 span 20557, May 7, 1996; USCG-2022-0323, 88 span 10032, Feb. 16, 2023 ]
