O P E N C A N O E t e C h N i Q u e
Trouble
brewinG
MAKING THE BEST OF BIG-WATER
BULLIES: BOils AND seaM liNes
IMAGINE YOU’RE ACCEPTING ACCOLADES for a perfect run of Coli-
seum on the Ottawa River when a boil in the outwash flips you and all
your credibility. If you’ve spent most of your paddling days on smaller
rivers, the seemingly random power of big-water boils and their seam
lines are likely to catch you off guard. Whether you’re in a solo playboat
or paddling a loaded tandem on a northern river trip, these features
demand your attention. With the right strategies, even the strongest
boils can be made a fun part of whitewater paddling.
Named for the appearance of the water, like a lobster pot on the
stove, boils are most common where there are powerful flows and
water depths of at least three metres. A boil on large volume rivers
like the Ottawa or Nahanni might be the shape and size of a pitcher’s
mound. To understand boils and seam lines we need to first consider
the movement of water in the vertical dimension.
Boils are caused by a current that flows upward, erupting on the
surface. It could be a current that was deflected by an obstruction on
the riverbed, in which case a boil will be pretty consistent and station-
ary. Or it might be a fast-moving current that collides with a slower one
and is forced upward, creating an inconsistent boil that surges and
dissipates, or reappears up- or downstream.
Seam lines form at the edge of a boil’s mound. Where there is water
coming up, there’s water moving down to fill the void. Seam lines are
like vertical eddylines formed where diverging vertical currents meet.
Boils can be distinguished from whirlpools—another big water fea-
ture—by how and where they form. Whirlpools typically appear near
the top of deep, strong eddylines and move downstream where they
dissipate. Boils and seam lines usually form further downstream where
the eddyline is less distinct.
Knowing where and how these features form helps you to avoid
them. Avoidance is your first and best strategy. Plan your moves ahead
so you don’t have to turn too aggressively and kill your speed in an
unstable situation. If you are going to hit a boil, you’ll have to paddle
uphill to get over the mound. Approaching with speed and continu-
ing to paddle maintains your momentum across the boil and makes it
easier to steer when you reach the seam line.
Cross seam lines at 90 degrees whenever possible and move away
from them quickly. These are often the trickiest part of the boil since the
water is pulling down on one side of your boat and pushing up on the
other. The same loose hips you use to stay balanced atop the surging
mound will allow you to make the quick adjustments needed to coun-
teract the seam line’s opposing forces.
In the event of a capsize, boils, seam lines and whirlpools can make it
difficult to roll. If you do swim, hang onto your boat—the downward cur-
rents in strong features can outweigh the buoyancy of your PFD, taking
Boiling point.
you momentarily below before firing you back up to the surface.
Photo RiCK MatthewS MARk SCRIVeR is a Black Feather guide and esquif team paddler.
www.rapidmag.com 21
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