 On March 26th at the Mayne Island church house, instructor Blair Smith provided a group of 14 students an introduction to Tides and Currents. He covered a lot of material. I'll provide some of the highlights of this talk beginning with some important definitions. Tides and currents are both displacements of water: Tides in a vertical (up and down) vector; currents in a horizontal vector.  Tides are controlled by the pull of gravity by the Earth, the Moon, and the Sun. The Earth's gravity acts similarly on the oceans all around the planet; it's the gravitational effects of the Sun and Moon that causes tides. However, it's the Moon, being much closer to Earth than the Sun, that has the biggest impact on tides. As the image here shows, The Moon's gravitational pull creates a bulge towards the moon on one side and an inertia bulge away from moon on opposite side. Since the Moon is in motion around the Earth we often get ups and downs more than once per day. If the sun and moon are in the same plane there can be an additive effect and these are called Spring Tides. This works if Moon and Sun are on opposite sides of the earth or on same side (new moon or full moon) generating the highest high tides and lowest low tides. Tides can cause wavy, bumpy water even when there is no wind due to lots of water moving and getting displaced. If the Sun and Moon are at right angles, however, there is a weaker pull on the water, and less movement up and down; these are called Neap tides. The result is less water displacement and often is a better time to be on the water safely, especially for activities involving paddling. Tide charts and tide tables allow boaters to determine how much water is below for safe navigation etc. These charts use a point called "Datum" as a reference level of water starting point. Height of tides is a difference between Datum and level of water at any given time. The depth of water is from Datum to the bottom. It's important to note that Datum in USA is not same as Datum in Canada. Stand refers to the transition point between rising and falling tides when the water depth is not changing. Currents refer to the horizontal movement of water. When water rushes to fill as tides change you get changes in currents. The water must move horizontally to raise and lower water height. Consider a 3 meter increase in water depth around Mayne island from low to high tide: all of that water is moving from the ocean to the channels around the islands. A smaller change due to Neap tide might result in a weaker current than the large changes in water depth brought by a Spring tide. Here are some terms related to currents:
 Reference books like Waggoner Ports and Passes have current charts for reference and secondary ports; they are not intuitive. The currents may be quite different in times and flow rate at secondary ports. You must look it up to be in the know and prepared. Blair had a few reference books like this including Current Atlas which I had mentioned in a previous course note (see Hotspots around Mayne Island). Our instructor shared a variety of navigation tips. Here are some of them that I was able to take down. Blair suggested you plan to do the more difficult part early in the trip. For example, ride against the current just before slack and when it switches you will be pushed by the current the rest of your trip. He also covered the "Rule of 12s" for estimating tide height: time of a tide is approx. 6 hrs. Tide charts will tell you how much the depth will change over that time period. In first hour you do 1/12 of the total change in tide over the 6 hrs. in second our do 2/12, then 3/12, 3/ 12, 2/12, 1/12. A simple calculation like this might be the difference for how far from the water to place your tent so it doesn't get wet overnight on those kayaks excursions. In a channel the water is moving its slowest near the shore (slowed by boulders etc). To move the fastest, get to the centre of the channel, actually in the tongue of the channel (water moves in a wedge with eddies on the sides). Eddies can be dangerous. You can use the Eddies to move you faster against the current, especially when closer to slack where they are more friendly. When passing an obstruction: give it room since the current is pushed to both sides of the obstruction and after the obstruction it rushes in and down and that could pull a boat under. Similarly, a ledge can be problematic and should be approached with caution. Wind and current in same direction and stretch out the waves and they will be less of a problem. Wind over current can produce very rough seas. Also, cold air is heavier so the wind is more damaging when air temperature is lower. As I said above, Blair covered a lot in the almost 90 minute class and answered many questions. If you are able to attend one of these classes (and there are several every spring on Mayne Island) then you will likely learn something that will make your time on the water more enjoyable and safer. Lastly, if you have questions for Blair, leave them in the comments and I'll ask him to provide an answer.
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