Presentation on theme: "Tides for Sea Kayakers. Overview What is a Tide? Types of Tides – Spring and Neap High and Low Tides Rule of Twelfths Calculation of Tides at Secondary."— Presentation transcript:
Tides for Sea Kayakers
Overview What is a Tide? Types of Tides – Spring and Neap High and Low Tides Rule of Twelfths Calculation of Tides at Secondary Ports Calculation of Currents at Secondary Stations Tide Races and Over falls Tidal flow direction
What is a Tide? Tides are the vertical rise and fall of the ocean level due to the gravitational and centrifugal forces between the earth and the moon and to a lesser extent the sun.
High and Low Tide High tide is when the water stops rising (Also known as High Water). Low tide is when the tide stops dropping is Low Water or low tide Slack Water is when there is NO movement of water in either direction.
Semi-diurnal Tidal Pattern In general in most of the world, the tides go up and down on a semi diurnal curve. A Semi-diurnal tide has two high tides and two low tides in a lunar day (24.8 hours).
Diurnal Tidal Pattern A Diurnal tide is a tide with one low and one high tide in a lunar day (24.8 hours).
Mixed Tidal Pattern Mixed tides are a diurnal and a semi-diurnal tide within the same geographic area. Mixed Semi-Diurnal Tides have two different ranges in tide levels
Tidal Patterns For kayakers to remember: A Diurnal Tide has a 24 hour 50 min cycle. A Semi Diurnal Tide has a 12 hour 25 min cycle.
Tidal Patterns Around the Earth
Cause of different Tidal Patterns
The Four Phases of the Moon
Rule of Twelfths Consider the general rule of twelfths: The flow of water between low and high tide is divided into a 6 hour period. The first hour will move 1/12 of the total volume of the tide. The second hour will move 2/12. The third hour will move 3/12. The fourth will move 3/12. The fifth hour will move 2/12. And The sixth hour will move 1/12. As a result the middle two hours move roughly half of the tidal volume.
TIDAL FLOW Tidal flow can be augmented by a number of factors: Shallow water Headlands Constrictions Wind direction
Tidal Races and Overfalls
Reading Tide Tables If we were to plan a paddle up Indian Arm launching at Deep Cove on Saturday October 5 when would it be a good time to launch? VANCOUVER DayTimeFeetMeters SA SU SECONDARY PORTS VANCOUVER HIGHER HIGH WATERLOWER LOW WATER TIME MEAN TIDELARGE TIDETIMEMEAN TIDELARGE TIDE DEEP COVE REFERENCE PORTS TABLE 2 HIGHER HIGH WATERLOWER LOW WATER MEAN TIDELARGE TIDEMEAN TIDELARGE TIDE VANCOUVER
Reading Current Tables. REFERENCE SECONDARY CURRENT STATIONS TABLE 4 (page 135) TIME DIFFERENCES % REFERENCE RATE TURN TO FLOOD MAXIMUM FLOOD TURN TO EBB MAXIMUM EBB FLOODEBB FALSE NARROWS DODD NARROWS OCTOBER 2013 TURNSMAXIMUM DAYTIME KNOTS SA (page 97) You have to catch a Ferry back to the mainland at Departure Bay on October 19 th and have to travel North though False Narrows, when would you attempt this in a kayak? Hint: A Flood tide travels north through False Narrows – from marine chart.
Tide Take-aways Know your tidal type (mixed, diurnal semi-diurnal) Know when high and low tide occur Know when neap and spring tides occur Know the rule of twelfths for peak flow Check the tidal tables before getting on the water Be aware of tidal races and where they occur Be aware of tidal directional flow and it’s variance around land masses