RE: [Paddlewise] Eddy currents and down river racing

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PeterO wrote:
>>>As the river has significant tidal currents many of us make use of eddy
currents near the shore when the tide is running against us. But its all
guess
work. The river is very wide so paddling from one side to the other to work
out if theres an eddy would waste valuable time. Question is are there some
rules of thumb that can be used to predeict which side of the river an eddy
is
likely to be running counter to the tide? Would it always be the shallow
side,
or up stream or down stream of the concave or convex side of a bend ? Are
their other parameters to consider?
I'd be keen to hear if anyone has develioped any rules of thumb or at least
has a theory that could be tested.<<<<

I'd suggest you read some texts on Downriver racing and then apply what you
learned to how the conditions will change when the current reverses. If the
current only reverses a small amount of the time the river bottom probably
stays much like a river with no reversing currents. With a standard river the
deep and fast water is always at the outside of curves and the shallows are
shallowest below the inside of the curve points. The temptation is always to
take the shortcut rather to stay in fast water but loss of current speed,
backeddies and shallow water drag effects from wavemaking (less than 5' of
water--increasing the shallower it gets) and turbulence off the kayak dragging
on the bottom (under 18" deep water and increasing more as the distance from
your hull to the bottom is reduced--with a big jump in drag to a stop if the
water is shallower than your draft) usually mean that too much of a shortcut
will almost always be a mistake. Tha't the rule but there can be exceptions if
it could save you a lot of distance--something like a portage to skip a big
meander comes to mind.

Coming upstream you would want to stay out of the downstream strong current
but be careful to avoid too much shallow water that will cause wave and bottom
drag. The really interesting time (and where if you figure it right, you might
be able to make up the most time against your competition) would be when the
current in the channel reverses but the bottom contours of the river haven't
changed. This might make for faster water over some of the shallows and eddies
that are deeper and this may make the conditions much more tolerant of taking
shortcuts.

If possibe try to paddle the course several times (with a racing buddy) ahead
of time when the currents will be similar to race day. Take different courses
at the turns and see who comes out ahead. Make notes on a map or drawing of
the river to use on race day.
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