BALSA, hiil'sii (Sp., Port., from Peruv. baba, a light wood, of which rafts are made). A raft or float, used originally for carrying passengers across a river or for landing in the surf. It consists of two floats—commonly made of logs from the balsa-tree, the wood of which is al most as light as cork—separated a short dis tance from each other and held in that position by a framework. It has been used in South America for centuries; it sometimes consists, as on the coast of Brazil, of several sharpened logs held together by slats; and, used by fishermen, is often met far out at sea. On the western coast of South America balsas are made of bullock hide sewn together over a framework to form a body of nearly circular section, pointed and turned up at the ends; two of them are joined together by a framework to which they are lashed. The balsa must be regarded as a develop ment of the raft principle. and is analogous to the pirogue. prow, Banta, catamaran, and other out-rigger boats of Asia and the Pacific islands.
The balsas used in the navy are composed of two floats joined by a framework, over which are laid slats about an inch apart. Each float is about 10 feet long, of oval section, but somewhat flat tened on top and tapering slightly from the centre toward the ends, built up of staves and banded like a barrel. The width of naval balsas is about two-thirds the length. Larger sizes have been issued, but they are not now supplied. The India-rubber balsa' has been used on shipboard more or less since 1837, but since the advent of collapsible boats its use has decreased. It is composed of two or more cylindrical. air-tight bags, with apparatus for inflating them, and a framework and raft-body to hold them together and afford a platform for passengers or freight. It is comparatively light and portable, but takes up much deck room, and the rubber deteriorates rapidly.