Double Bottom

Twin layer of shell plating with the inner-bottom forming the cargo hold or tank floor; required on most cargo vessels for damage stability and ballast.

Regulatory detail & full definition

MARPOL Annex I Reg. 19 mandates double bottoms on oil tankers >5,000 DWT. Height varies with vessel size (B/15 minimum for tankers, typically 1.0–2.5 m). Provides ballast capacity, damage protection, and walkable inspection space.