Near both ends of the centre spar there is cut a perpendicular slit, about a couple of inches wide by one or two feet in length.

Into each of these holes a broad plank, called guaras by the natives, is inserted in such a way that it may be thrust down to the depth of ten or twelve feet, or it may be drawn up entirely.

The slits are so cut, that, when the raft is in motion, the edges of these planks shall meet the water.

It is clear, that if both the guaras be thrust quite down, and held fast in a perpendicular direction, they will offer a broad surface towards the side, and thus, by acting like the leeboards of a river-barge, or the keel of a ship, prevent the balsa from drifting sidewise or dead to leeward.

But while these guaras serve the purpose of a keel, they also perform the important duty of a rudder, the rationale of which every sailor will understand, upon considering the effect which must follow upon pulling either up the guara in the bow or that in the stern.