Re: [Paddlewise] Tides & Currents

As a local oceanographer and kayaker with some experience in and
knowledge of the San Juans and similar regional waters (although not
as much as K. Whilden's fabled employer at Kayak Academy), I would
like to make several points of fact and/or opinion:

1) The other answers to Clyde's question, regarding Mauritius, did not
seem to address his point about "tidal" as opposed to "ocean"
currents. Tidal currents are inherently oscillatory with about a 6.25-
or 12.5-hour average period, depending on location. Hence Clyde's
suggestion that if one could stay with (preferably IN) the boat long
enough, one should return to one's approximate starting point in half
a day at most. Large-scale wind-driven ocean ocean currents (such as
those around Mauritius), in contrast, are generally unidirectional for
long periods of time. Any prevaling local wind and wave transport
would add to the latter hazard. 

2) In a statistical sense, Kevin may be correct that "currents usually
are not faster than fast paddling speed," i.e., over a majority of the
area for a majority of hours on an annual basis. However, there are
several channels in the San Juans where currents exceed 2-3 knots over
most of their width and length for several hours a day and for several
successive days during spring tidal periods (around new/full moon),
especially during May-July and November-January. That's fast for me to
paddle for a period of hours (shorter burst are OK). Maximum currents
exceed 4 knots in many areas during these times. Thus I would argue
that strong currents are common enough to get the uneducated paddler
into conditions where he/she could not control his/her position for
several hours at a time. P.S. This happened to me in my greener years.

3) Many experienced paddlers I've met also seem to assume that slack
currents are synchronous with high and low water. In the San Juans, as
in many other narrow channels, however, currents and water levels are
commonly (not always) out of phase, often by as much as 1-2 hours or
more. Failure to read tidal current tables instead of tidal height
tables is particularly dangerous where high/low water occurs AFTER
slack, such as occurs in Deception Pass (8 knot maximum currents), so
that the unwary paddler would potentially launch into an accelerating
current.

4) There are large open-water areas in the San Juan vicinity, as well
as long channels, both of which may have strong currents over broad
areas (tens of miles). It is not hard for a paddler to piggyback tidal
currents intentionally for 10-12 miles on a  single tidal cycle in
some places, so the displacements in an accidental scenario can be
greater than what Clyde is visualizing. Furthermore, distance from
shore would logically seem to diminish the odds of rescue.

5) The complex current patterns in the San Juan area, including large
scale eddies and significant differences in the timing of current
stages over short distances, could easily result in a paddler not
being able to retrace his/her path when the current reversed, but
rather being entrained into another channel altogether.

6) The bottom line, to amplify Kevin's point, is that being "swept out
to sea" is not so much the issue (in the San Juans, anyway), so much
as being swept uncontrollably into areas with hazardous conditions
such as eddylines, tide rips, high seas, or oil tankers :-(.

Thank you for listening to my sermon.

Richard Strickland
Seattle

---"K. Whilden" <kwhilden_at_u.washington.edu> wrote:

> If I recall correctly, most of the accidents involving currents in
Deep
> Trouble were problems specificly associated with crossing eddylines.
The
> eddyline caused a flip, thus leaving the paddler at the mercy of the
> currents. 

[SNIP]

> In the San Juans at least,
> the currents usually are not faster than fast paddling speed except
for
> localized areas near shore where the current speeds up (e.g.
eddylines and
> tide rips). These local areas are fairly easy to paddle around,
given a
> rudimentary knowledge of currents and eddylines. Sometimes though,
it is
> impossible to avoid being swept into an eddyline...

> On Tue, 26 Jan 1999, Sisler, Clyde wrote:
> 
> > I was struck by the number of times tidal currents played a role
in the
> > accidents in the book Deep Trouble.  The term 'swept out to sea'
stirs up
> > some pretty scary images but how bad can it really be?  Given that
a person
> > can stay in the boat, how far out can they be swept?  A mile, two
miles?
> > Even at full ebb, the tidal (not ocean) current has to dissipate
somewhere.
> > 
> > Granted one might well spend some uncomfortable hours and then
have to
> > paddle back, but still......


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