double bottom

A double bottom is a hull construction where a ship has two layers of plating—an inner and outer bottom—creating a void space that provides protection against flooding if the outer hull is breached.

The space between often holds fuel or ballast water.

In technical analysis of financial markets, a double bottom is a chart pattern resembling the letter W, where a price drops to a low point twice before rising—considered a bullish signal indicating a potential trend reversal.