What statement is true concerning watertight doors fitted below the waterline of a vessel?

Correct Answer: Option B — Watertight doors below the waterline may be either of the vertical or horizontal sliding type.

46 CFR Subchapter F and SOLAS requirements mandate that watertight doors below the waterline must be power-operated sliding doors. These are either vertical or horizontal sliding types to ensure they can close against a head of water, whereas hinged doors are generally prohibited below the waterline.