Tides and Currents

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Tides and Currents

• By
• Andree Hurley
• ACA Instructor Trainer Coastal
• and Whitewater Kayaking
• Onwatersports.com!

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Planning a kayak trip in Japan?
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A definition

• Tides
• Vertical Movement of water
• Mostly affected by the rotation of the earth and
  gravitational pull of the moon

• Currents
• The resulting horizontal movement of the water.

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Phases of the Moon Affect the Tide

• New Moon and Full Moon have a lot of
  gravitational pull resulting in higher and lower
  tides
• The moon takes 24 hours and 52 minutes to travel
  around the Earth. This mostly produces two high
  and two low tides each day. These are called
  semi-diurnal tides. Each tide is about six
  hours. The tides change by about an hour each
  day. If high tide is at noon today, it will be at
  about one oclock tomorrow.
• When the sun and moon and Earth are in a straight
  line, during the times of a full moon and new
  moon, the gravitational pull on the Earth is the
  greatest. It creates high tides that are very
  high and low tides that are very low. These are
  called spring tides.
• When the sun and moon are at right angles to each
  other they pull in opposition to one another, and
  the difference between high and low tides is not
  very great. These tides are called neap tides.
• Department of Fisheries and Oceans Canada
• http//www.glf.dfo-mpo.gc.ca/sci-sci/bysea-enmer/a
  bout-ausujet-e.html

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Tide Charts
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• The publication of full daily predictions is
  limited to locations referred to as "reference
  stations".
• The remaining stations are referred to as
  "subordinate stations".
• Tidal predictions for the subordinate stations
  can be obtained by applying specific differences
  to the times and heights of tides at the
  specified reference stations.

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• http//tbone.biol.sc.edu/tide/sites_uswest.html

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How Tide Affects Kayakers

• Long (muddy) carries!
• No beach at all
• Secure your kayaks!

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Vertical Movement in Tide Creates Horizontal
Movement in Current

• During the New and Full moons, the current is
  fastest as more water has to move through the
  same space
• The rest of the time, currents tend to be slower
  moving.

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• Figure 1 Tidal current transports (current
  velocity times ocean depth) for the principal
  lunar tide in the Indian Ocean, at the instant
  when the mean moon passes the Greenwich meridian.
  
• Within the central Indian Ocean, high tide
  occurred several hours earlier, and the water is
  now rushing away from that point.
• Flood tides are occurring in the Timor Sea and in
  the Bay of Bengal.
• These data were determined from TOPEX/POSEIDON
  altimetry.

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Primary Stations

• http//www.dairiki.org/

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Current Charts
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• http//co-ops.nos.noaa.gov/currents06refcurrents.h
  tml

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Some Terms

• Slack
• Flood - maximum flood
• Ebb - maximum ebb
• Rule of thirds

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For example - kayaking into Deception Pass. I
like to paddle into the pass on the tail end of a
flood, wait for slack, play in the eddies During
the beginning of ebb, and get the free ride back!
900 am- slack before flood 1000 am- 50 max
flood 1100 am- 90 max flood 1200 pm 100
max flood (six knots) 100 pm 90 max flood 200
pm 50 max flood (enter pass) 300 pm slack
before ebb (hang out, watch pigeon
gillemots) 400 pm 50 max ebb (work
currents) 500 pm 90 max ebb (think about
leaving, free ride) 600 pm max ebb (six knots)
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Bathtub Effect - Like the Sea of Cortez (Mar de
Vermillon)
In 1940, Steinbeck and his biologist friend
Edward Ricketts took a sardine boat out of
Monterey on a 4,000 mile trip around the Baja
peninsula into the Sea of Cortez.
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Water has momentum. Like a ball on a pool table,
it moves in a straight line until it hits
something and is deflected. The earth continues
moving under the mass of water - so we can can
still have current going in one direction even
though the tide has changed.
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How Does This Affect US

• We could be paddling against current and going
  nowhere!
• We want to look for the free ride
• We might get stuck in an eddy
• We need to enter and exit eddies - some as long
  as an island

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Interactive Portion of Presentation
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Now You Do It!

• We are going on the last leg of our trip - from
  Cypress Island to San Juan Harbor. We will cross
  a shipping channel (dangerous) and two bodies of
  water with two different current stations,
  Rosario Straits and San Juan Channel. You choose
  the route and the times you will leave, eat lunch
  and arrive!

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