The Australian Overlapping-Triangle Raft

Reader Geoff Cater steered me toward his fine summary page of indigenous Australian watercraft where, along with excellent images of various canoe types, there are a number of rafts.

The type that I find most intriguing consists of two triangular platforms, one stacked atop the other and facing in opposite directions. In two of the examples shown, fastening on each layer is by means by wood rods inserted through holes bored through the logs. In the model, the logs are fastened to their neighbors with thread, which may indicate lashed construction on the example from which the model was based, or might have been simply the modelmaker's expedient. Also in the model, the layers are attached to one another with a nail; it's unclear how the layers are attached in the other examples.

The photos and captions below are borrowed directly from Mr. Cater's webpage, for which thanks are given.

1931: A model raft made from six cylindrical wooden rods, collected in 1931 by Gerhard Laves from Bardi people at Cape Leveque, WA. Description: A model raft made from six cylindrical wooden rods with pointed ends and joined together with thread. A second "deck" of five pointed cylindrical wooden rods are attached to the first with a metal nail. Source: National Museum of Australia.

1931-1994: Double triangular raft, pole and paddle, Western Australia. Illustration by Xiangyi Mo. Barlow: Aboriginal Technology: Watercraft (1994) page 27. The illustration by Xiangyi Mo is possibly based on the model raft held by the NMA, above. The grass matting is possibly represents a seat or, if mixed with mud, a hearth for the fire often carried on board. Below are a punting-pole and a short-staffed spoon or pudding-stirrer paddle, as used by George Water in the photograph [below]. Their use throughout the continent and Tasmania indicates the pudding-stirrer's great antiquity, perhaps back to the last of the migrations from SE Asia.

1916: Worora youth on a mangrove tree raft (or 'kaloa'), George Water, Western Australia, 1916. Photograph by Herbert Basedow (1 of 2). Basedow, Herbert: The Australian Aboriginal. F.W. Preece & Sons, Adelaide, 1925, plate 22.
National Museum of Australia

In the model and, apparently, in the 1916 photo, the ends of the two layers line up pretty well. In the drawing, the two layers are offset, so that the logs' wider ends extend beyond the other level.

Why did the raftmakers face the two triangles in opposite directions? If two layers of logs were needed for buoyancy, it might make more sense to place the narrow ends one atop the other to form a roughly conventional "bow," since a forward-pointing triangle is more hydrodynamic. 

But as the photo shows, the bottom layer seems to provide enough buoyancy to hold the top layer and its passenger nearly or entirely clear of the water. By reversing the directions of the triangles, the logs of the top one do not nestle between the logs of the bottom one, so the top one actually rides higher and drier, while the forward-pointing triangle on the bottom still provides the desirable hydrodynamic efficiency.

Both the drawing and the photo show short, one-handed "pudding stirrer" paddles, and the drawing shows a pole as well: no doubt poles were commonly used for propulsion in shallow water.