The case against single chine river boats.

[river runner]

The sigle chine, flat bottom boat has three potential (notice I said potential) advantages.
1. It is easy to build.
2. It can be shallow draft.
3. It can have good primary stability.

But these advantages come at a cost. Seems that nothing is free in boat design. The disadvantages of a single chine boat, specifically for river use, are:
1. You can catch an edge in a boat just like you can on skis. On a river, you aren't always in line with the current. When you are sideways to the current, the sharp corner of a single chine boat can catch on rocks or slower moving water.
2. Single chine boats have a higher wetted surface area than multi-chine or round bottome boats of the same size and shape.
3. Single chine boats tend to have poor final stability. As they are leaned over, once they reach a certain point, they suddenly and dramatically dump you in the river. A multi-chine or round bottome has a more steady, even progression and will tip farther before the gunnel is in the water.
4. Single chine boats limit your design options. You have more flexibility in shaping your hull the more chines you have.
5. Single chine hulls are less attractive. It's hard to get sensuous curves with a single chine.

[TeddyDiver]

Originally Posted by river runner

1. You can catch an edge in a boat just like you can on skis. On a river, you aren't always in line with the current. When you are sideways to the current, the sharp corner of a single chine boat can catch on rocks or slower moving water.

In the case of rocks it's irrelevant weather its single, double or round chine. Upside down you go. And it doesn't allways help much if you stay in line with the current either..
There's one hull material thou which is more forgiving.. ethylene, it's very slippery against the rocks and softy so it's never a hard crash.. But it has other drawbacks.

[DCockey]

Originally Posted by river runner

.....
3. Single chine boats tend to have poor final stability. As they are leaned over, once they reach a certain point, they suddenly and dramatically dump you in the river. A multi-chine or round bottome has a more steady, even progression and will tip farther before the gunnel is in the water.
......

Depends on the amount of flare in the sides, width of the bottom, and depth of the boat. Wide, shallow boats with almost vertical sides behave as you describe. Boats with narrow bottoms, strong flare to the sides and deep may become stiffer when heeled.

[messabout]

Your premise number 3 is not invariably correct, Particularly that round chines will heel at a larger angle before the rail is down. As a matter of fact a plumb sided boat will endure larger angles of heel before rail down is reached. That is not to infer that flare sided boats have less progressivly increasing righting moment.

Flat bottomed boats typically produce increasing righting moment as they are heeled. The increase is not a linear function however. Increase in RM per unit of heel diminishes as the heel angle increases. A typical small skiff will go rail down somewhere in the region of 35 degrees more or less. After the critical rail down condition....the swimming begins.

Whether the boat, regardless of chine configuration, is flipped depends to a large extent on how the weight is distributed in the boat. A small boat in heavy weather can sometimes be saved by the simple expedient of sitting on the floor.