46 CFR § 178.450 - Calculation of drainage area for cockpit and well deck vessels.
---
identifier: "/us/cfr/t46/s178.450"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "46 CFR § 178.450 - Calculation of drainage area for cockpit and well deck vessels."
title_number: 46
title_name: "Shipping"
section_number: "178.450"
section_name: "Calculation of drainage area for cockpit and well deck vessels."
chapter_name: "COAST GUARD, DEPARTMENT OF HOMELAND SECURITY"
subchapter_number: "T"
subchapter_name: "SMALL PASSENGER VESSELS (UNDER 100 GROSS TONS)"
part_number: "178"
part_name: "INTACT STABILITY AND SEAWORTHINESS"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "43 U.S.C. 1333; 46 U.S.C. 2103, 3306, 3703; E.O. 12234, 45 FR 58801, 3 CFR, 1980 Comp., p. 277; DHS Delegation No. 00170.1, Revision No. 01.3."
regulatory_source: "CGD 85-080, 61 FR 966, Jan. 10, 1996, unless otherwise noted."
cfr_part: "178"
---
# 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
<sup>2</sup> = 4389.12 × [(Recess Volume × Recess Ratio) + (Weather Deck Volume × Weather Deck Ratio)]; or
Basic Drainage area in inch
<sup>2</sup> = (Recess Volume × Recess Ratio) + (Weather Deck Volume × Weather Deck Ratio)
Recess Volume = (B<sub>R</sub> × D<sub>R</sub>) − V<sub>R</sub>
B<sub>R</sub> = average height in centimeters (feet) of the bulwark above the well deck or cockpit deck;
D<sub>R</sub> = total deck area of the cockpit or well deck in the after
2/3 of the vessel length (LOD) measured in centimeters
<sup>2</sup> (feet
<sup>2</sup>).
V<sub>R</sub> = volume of any weather tight structure below the bulwark of the well deck or cockpit deck.
Recess Ratio = L<sub>R</sub> / L<sub>C</sub>
L<sub>R</sub> = the length of the recess in the after
2/3 vessel length (LOD).
L<sub>C</sub>=
2/3 vessel length (LOD).
Weather Deck Volume = (B<sub>D</sub> × D<sub>D</sub>) − V<sub>S</sub>
B<sub>D</sub> = average height in centimeters (feet) of the bulwark above the weather deck;
D<sub>D</sub> = 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
<sup>2</sup> (feet
<sup>2</sup>).
V<sub>S</sub> = volume of any weather tight superstructure below the bulwark on the weather deck located within D<sub>D</sub>.
Weather Deck Ratio = L<sub>D</sub> / L<sub>C</sub>
L<sub>D</sub> = the length of the weather deck bulwark in the after
2/3 of the vessel length (LOD).
L<sub>C</sub>=
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 ]