Tides and Currents By Andree Hurley ACA Instructor Trainer Coastal and Whitewater Kayaking Onwatersports.com!
Planning a kayak trip in Japan?
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.
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 o’clock 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
Tide Charts
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.
How Tide Affects Kayakers Long (muddy) carries! No beach at all Secure your kayaks!
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.
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.
Primary Stations
Current Charts
Some Terms Slack Flood - maximum flood Ebb - maximum ebb Rule of thirds
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! 9:00 am- slack before flood 10:00 am- 50% max flood 11:00 am- 90% max flood 12:00 pm 100% max flood (six knots) 1:00 pm 90% max flood 2:00 pm 50% max flood (enter pass) 3:00 pm slack before ebb (hang out, watch pigeon gillemots) 4:00 pm 50% max ebb (work currents) 5:00 pm 90% max ebb (think about leaving, free ride) 6:00 pm max ebb (six knots)
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.
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.
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
Interactive Portion of Presentation
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!