The correct answer is A) provide drainage from the decks. Beams are cambered, or slightly arched, to allow for water drainage from the decks. This helps prevent water accumulation and pooling on the deck surfaces. The cambered shape of the beams creates a slope that facilitates the natural drainage of water, which is an important safety and maintenance consideration on vessels. The other answer choices are incorrect because increasing beam strength (B) and relieving deck stress (C) are not the primary reasons for camber. While camber can provide some secondary benefits in those areas, the main purpose is to enable proper water drainage from the deck surfaces.