Hull Designs

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Canoes, Rivers, and Hull Designs

As I mentioned, guessing effective dugout hull design is difficult because a modern canoe "floats," weighing perhaps 400 pounds with two people, drawing maybe two to four inches of water, while a 2,400 pound dugout with a 7-inch thick floor is a "battleship" with ballast, a heavy hull a foot down in the water, and the center of gravity low. How these two crafts react differently to side currents is a major part of our puzzle. Most people think a long, narrow log will turn over easily. However, I had traveled extensively in Borneo by 35-foot hollowed log in big, swift rivers, and I knew that those huge hardwood logs were surprisingly stable.

The dynamics of a side current in a river is a bit counterintuitive. As the canoe crosses a current coming from the right (upstream), you might expect the boat to be thrown over to the left, downstream. Instead, it is rolled over toward the current by the force of the water rushing under the hull. That is, a canoe in a cross-current is rotated upstream, not downstream. Thus a lake canoe with a keel, catching the cross current as it flows under the boat, is very dangerous in rivers.

Figure 2

Hydrodynamics
Pass cursor over image to view details.

The tiny glistening wavelets to the right of this miniature replica of a modern canoe show that the current is piling up on the upstream side and dragging the starboard gunwale under water. The effect would be exacerbated if the craft were being cordelled around a shoreline obstruction such as a rock or stump.


Anything catching that side current will tend to rotate and tip the canoe upstream. That is also why a straight sided, flat bottomed boat with no chine, that is, sides and bottom meeting at ninety degrees, is much more likely to be rotated than a chined boat, with rounded sides to allow the cross current to slip underneath with a minimum of friction.

Since we do not have hull descriptions of the dugouts and we have very few journal entries on river tactics, especially when paddling, we will have to make some guesses about canoe design. However, we do know some important facts: a) Experienced river men, American and French-Canadian, in an age of river travel, were present when the first boats were built near the Mandan villages, and worldwide, sophisticated canoe designs are thousands of years old. b) The expedition had excellent leadership, and we can assume they did not make silly canoes. c) A dugout canoe could be taken across the river by one paddler without difficulty; on June 24, 1805, Lewis "sent Shannon down the opposite side to bring the canoe over to me and put me across the Missouri." d) On the other hand, the boats were often cordelled in difficult situations. On May 25, 1805, Lewis explained:

the wind being against us we did not proceed with so much ease or expedition as yesterday, we imployed the toe line principally which the banks favored the uce off; the courant strong particularly around the points against which the courant happened to set, and at the entrances of the little gullies from the hills, those rivulets having brought down considerable quantities of stone and deposited it at their entrances forming partial barriers to the water of the river to the distance of 40 or 50 feet from the shore, arround these the water run with great violence, and compelled us in some instances to double our force in order to get a perorogue or canoe by them.

Why did they not cross the river at these "barriers," as usual? On the next day, May 26, Lewis remarked, "proceeded principally by the tow line, using the oars mearly to pass the river in order to take advantage of the shores."

Figure 3


As a modern canoeist, I began this project with a prejudice: I suspected that the square end, flat bottomed, straight sided "Clearwater Canoe" (also known as the "Lewis & Clark" canoe because it may have accompanied the party down the Clearwater and Snake for a few days), while described clearly and therefore valuable to scholars, is probably not a good model.

 

Worldwide, such punt/scow/barge designs are made partly for a man standing up, usually while fishing, to see into the water and spear a fish or throw a net. They can also carry cargo over short distances, and cross the river near the village. However, such blunt end, sharp sided boats are not good for ascending and navigating fast current over distance; the bow does not cut the water efficiently, and the sharp sides, while they feel secure when you get in ("initial stability") can be tipped over by a side current.

Figure 4

Moreover, a squared boat requires extra effort in hacking a log. I assumed that the Fort Mandan dugouts were not scow design.They were probably part flat-bottomed but with rounded chines, and a moderately sharp entry line, though thick and strong (more like the Nez Perce "Spalding" canoe). It is true that the party's "stout canoes" were upstream freight carriers, but they also had to be riverworthy. They also would have been made as light as possible, to maximize the payload in relation to displacement. A heavy dugout hull, however, is not the same as a skimming boat, whether it is made of bark, or skins, or Royalex, so I knew that my modern canoe prejudice might be irrelevant. And yet, the Borneo dugouts had slightly rounded bottoms, and rounded chines, and sometimes slightly V-shaped bottoms. A real, dramatic river test was the only way to tackle these issues. How does a log paddle in real water – say, the Missouri in flood?


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