Calculation of drainage area for cockpit and well deck vessels.

(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 = (B R × D R ) − V R B R = average height in centimeters (feet) of the bulwark above the well deck or cockpit deck; D R = 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 ). V R = volume of any weather tight structure below the bulwark of the well deck or cockpit deck. Recess Ratio = L R / L C L R = the length of the recess in the after 2/3 vessel length (LOD). L C = 2/3 vessel length (LOD). Weather Deck Volume = (B D × D D ) − V S B D = average height in centimeters (feet) of the bulwark above the weather deck; D D = 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 ). V S = volume of any weather tight superstructure below the bulwark on the weather deck located within D D . Weather Deck Ratio = L D / L C L D = the length of the weather deck bulwark in the after 2/3 of the vessel length (LOD). L C = 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; USCG-2022-0323, 88 FR 10032, Feb. 16, 2023 ]