Richard Dewey RVYC / UVic  Swiftsure.org Web Site Race Info  Currents During Race [email protected]

Tidal Heights and Currents

Tidal currents “flood” in from the ocean on a rising tide and “ebb” out to the ocean on a falling tide.

Surface Slope Drives Tidal Currents  Currents 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 “sieches”.  Mean flows in June: surface water exiting Salish Sea (¼-½ knot), some of this is in the tidal current table values. Weak ( ≈ ¼ knot) in 2015

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), can be slower & will stop and reverse sooner.

 Lateral convergence or vertical shoaling can result in accelerated flows.

Points of Sail in a Current

 Although the speed of the current is low compared to the wind (hopefully), a few knots of current 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 always better than on the windward side: apparent wind and lift.

Tidal Current Station Tidal Height Station

Reading Tidal Height Tables

Victoria (CHS) PDT=PST+1

Tidal Height: May 23 – 25, 2015

Tidal Current Station Tidal Height Station

Reading Tidal Current Tables

Race Passage PDT=PST+1 1 knot = ~0.5m/s + flood - ebb

Tidal Currents: May 23 – 25, 2015

Foreman, et al, 2004

Tidal Currents: May 23 – 25, 2015

Good Luck!

At Swiftsure.org

 Race Info  Currents During Race (please save PDF files, don’t print  ) Richard Dewey [email protected]