46 CFR 178.450: 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 = (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.