1,103 bytes added,
17:21, 17 February 2016 = Double Hull/Double Planking =
A [http://en.wikipedia.org/wiki/Double_hull double hull] or double planking is found on the most expensive designs like [http://capehornyachts.com/ Cape Horn Yachts]. A double hull offers additional protection against hull penetration, e.g., by a log or shipping container. About 2,000 containers a year are lost overboard. Many of the smaller ones float for a long time. Containers 40-ft and under have weight limitations for the contents that are low enough to give the containers buoyancy if they are watertight. If they have only small holes and take on water slowly, they can take several months to sink.<ref>vero marine, http://www.veromarine.co.nz/dirvz/marine/marine.nsf/Content/Home</ref> Containers over 40-ft have no reserve buoyancy and probably sink right away.
A double hull has significant impact on displacement, centre of gravity and, of course, cost. Aluminum superstructures are often used to redress the increased weight.
A double bottom offers no protection from hull penetration by floating objects but does offer some protection from grounding.