Project Scope

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This preliminary report will outline the issues and describe the results of the first river tests, which were conducted on June 12, 2005, and will indicate areas of continuing research.

Figure 1

Anatomy of an Eddy

To see labels, point to the image.

Interactive photo of a river rapid

© VIAs Inc.

The river is flowing rapidly from right to left, perhaps as fast as 5-6 miles per hour. The water in the foreground is the upper part of an eddy, flowing upstream. The thin white line of foam is the eddy seam. The eddy current collides with the main current, creating the turbulence that is evident at extreme right.

Design, Performance, and Strategies

In this preliminary report I would like to solicit comments and advice from fellow canoeists and canoe scholars. I am particularly interested in what we do and do not know of hull design in relation to performance in the river, and therefore in relation to strategies in ascending or descending. The journals are almost silent on all three points.

Why is dugout design and performance important? The Corps, walking the shores or shallows with ropes and tugging their craft upriver, six canoes and two pirogues, has come to a big eddy; they look upstream and see an overhanging cut bank and cliff ahead, with fast, deep water at its base.

They see no option but to cross the river and haul the boats up along the opposite bank, which looks good for a few miles. An eddy on the Missouri in flood can easily travel upstream for a half mile and more. Could they use the upstream eddy for its full length up-river, and then cross through the turbulent eddy seam at the top? Or, fearing the vigorous current at the top, would they have to cross at the bottom of the eddy, and forgo use of a half mile of upstream flow? It made a lot of difference to them, many times a day: a half mile of easy pulling along with the current of the eddy, flowing upstream—if they dared cross the eddy seam at the top.

Another example: although these were freight canoes tracking upriver, they had to go cross current not just when paddled to the opposite shore, but also when cordelled. We know that the bow falling off (turning cross current) was a constant concern while cordelling; if the heavily laden dugout's bow turns out into the river just ten degrees from the line of the current, the pull on the bow rope is tremendous, and if the water cannot flow easily under the hull (because it is squared on the sides), the danger of tipping the boat upstream is real. Chines—rounded corners between the bottom and the sides—and a properly rounded bow, would help alleviate these cross-current problems. All of this the men knew when shaping the dugouts at Fort Mandan.

For a fuller discussion and demonstration of lining—or "cordelling"—a boat, see the following video, which demonstrates the principles of pulling a boat upstream from rough banks through fast water.

Funded in part by a grant from the National Park Service, Challenge-Cost Share Program