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TRANSCRIPT
Tidal Heights and CurrentsTidal currents “flood” in from the ocean on a rising
tide and “ebb” out to the ocean on a falling tide.
Surface Slope Drives Tidal CurrentsCurrents flow down-hill, from higher to lower
water.
Racers needn’t worry too much about tidal height, except when anchoring or rock hopping.
Local current patterns are determined by the channels, straits, and sounds in response to these ocean and basin “waves” or “sieches”.
Mean flows in late May: surface water exiting Salish Sea (¼-½ knot), some of this is in the tidal current table values. 2016: >¼ knot
Deep vs Shallow Tidal Currents
Deep water has more inertia, will ride “up-hill” to stop, reversals are lagged/delayed.
Shallow and boundary layer flows have more friction (turbulence/drag), can be slower & will stop and reverse sooner.
Lateral convergence or vertical shoaling can result in accelerated flows.
Points of Sail in a CurrentAlthough the speed of the current is low
compared to the wind (hopefully), a few knots of currents over time will make a difference.
Avoid currents on the windward quarter.
Heading into a tide, try to keep the tide under the leeward bow, (lee-bow).
A current under the lee side is always better than under the windward side: apparent wind and lift.
Tidal Current Station
Tidal Height Station
Reading Tidal Height Tables
PDT=PST+1Victoria (CHS)
Tidal Height: May 28 – 30, 2016
Tidal Current Station
Tidal Height Station
Reading Tidal Current Tables
PDT=PST+1Race
Passage
1 knot =
~0.5m/s
- Ebb
+ Flood
Tidal Currents: May 28 – 30, 2016
Flood
Ebb Start Rounding Finish
Race
Passage
JdF-W
JdF-E
1 m/s = 2 knots
Foreman, et al, 2004
Tidal Currents: May 28 – 30, 2016
Flood
Ebb Start Rounding Finish
Race
Passage
JdF-W
JdF-E
Good Luck!At Swiftsure.org
Race Info Currents During Race
(please save PDF files, don’t print )
Richard Dewey