(a)The drainage area required on a vessel must be computed using the following formula:
(b)Vessels with bulwarks in the forward part of the vessel shall not form a well with the deckhouse which retains water. For protected waters required drainage = .1 × Basic DrainageFor partially protected waters required drainage = .5 × Basic DrainageFor exposed waters required drainage = Basic DrainageBasic Drainage area in centimeters= 4389.12 × [(Recess Volume × Recess Ratio) + (Weather Deck Volume × Weather Deck Ratio)]; orBasic Drainage area in inch= (Recess Volume × Recess Ratio) + (Weather Deck Volume × Weather Deck Ratio)Recess Volume = (B× D) − VRecess Ratio = L/ LWeather Deck Volume = (B× D) − VWeather Deck Ratio = L/ Lwhere:B= average height in centimeters (feet) of the bulwark above the well deck or cockpit deck;D= total deck area of the cockpit or well deck in the afterof the vessel length (LOD) measured in centimeters(feet).V= volume of any weather tight structure below the bulwark of the well deck or cockpit deck.L= the length of the recess in the aftervessel length (LOD).L=vessel length (LOD).B= average height in centimeters (feet) of the bulwark above the weather deck;D= total deck area of the weather deck adjacent to bulwarks but not in way of the cockpit or well deck in the afterof the vessel length (LOD) measured in centimenters(feet).V= volume of any weather tight superstructure below the bulwark on the weather deck located within D.L= the length of the weather deck bulwark in the afterof the vessel length (LOD).L=vessel length (LOD).[CGD 85-080, 61 FR 966, Jan. 10, 1996; 61 FR 20557, May 7, 1996; USCG-2022-0323, 88 FR 10032, Feb. 16, 2023 ]