Here’s a question for you: How do you get a sailboat with a hull speed (maximum speed) of 6.5 knots to sail 35 miles in about four hours?
This isn’t a hypothetical question. Just the other day, we sailed our 39-foot sailboat, Polaris, to Port Townsend from Seattle in about four hours.
The answer is in the stars. Specifically, the sun and the moon, how close Earth is to either, and to a certain extent, the weather. These all have an impact on how deep the water is, how fast it is moving and in which direction it is heading. In short, tides and currents.
Puget Sound and Salish Sea have amazing tides and currents that have the power to affect how quickly you can get to a destination—or if you can get to that destination at all. That’s why it’s important to understand how tides and currents work in this area, and to always incorporate them into your trip planning.
What goes up must go down
The Salish Sea, of which Puget Sound is a part, gets its water from the Pacific Ocean thanks to the watery highway that connects the two: the Strait of Juan de Fuca. When the water rises for the Pacific, it brings gallons and gallons of seawater down the Strait and into the Salish. We call this the flood tide because that is when the water level increases in Puget Sound and around the San Juan Islands, so much so that it can completely cover things you don’t want to sail into, like big rocks.
When the water level drops in the Pacific, those millions of gallons of seawater go shooting back out the Strait. The water level drops for the Salish as well. We call this the ebb tide. The shore line can get a whole lot wider, often leaving places that were completely under water completely dry and visible, like those rocks you were trying to avoid.
Puget Sound’s big tides
In many places around the world the difference between the flood and the ebb is large. The Bay of Fundy in Canada has the biggest tide, with an average difference of 38 feet. In Puget Sound, the tide ranges from about 8 feet to 14 feet, depending on where you are, what time of day and when in the year. The Salish Sea has what are called mixed diurnal tides. That means that in a typical 24-hour period, there will be two low tides, with one much lower water than the other, and two high tides, with one much higher water than the other.
We also have what are called neap and spring tides. The University of Washington has a great explainer about Puget Sounds tides and what causes them, but for our purposes here, I will summarize: Spring tides have larger tidal ranges, neap tides have smaller tidal ranges.
Currents: Friend or foe?
During the flood, water coming down the Strait pushes south into Puget Sound and north into the San Juan Islands. When the tide begins to drop, the current runs north out of Puget Sound and south out of the San Juan Islands. These tidal exchanges create currents of varying speeds and directions.
The local topography also contributes to the speed of these currents. Water flowing through narrow passages functions just like water coming out of a hose that was been partially blocked at the end: it flows faster.
In general, it’s best to ride the current when it is going the same direction you are going. Going with the current speeds you up; going against it slows you down. However, in some places the current speed can get so fast it would be dangerous for your average sailboat to go during the max current, regardless of which direction it is going.
Where the currents are fast
Examples of places in our local waters where the flow gets “squeezed” into going faster include the Tacoma Narrows and Deception Pass, where the current often gets above 6 knots going either direction. British Columbia has some incredibly fast currents that require careful planning. The current going through Seymour Narrows, for example, can reach speeds of over 15 knots.
In those cases, it’s best to wait for a time when the water level is neither falling nor raising, creating little current at all. This is called slack.
Using tides and currents to plan your journey
The key to navigating around these variables is to always check tide and current predictions, and time your voyage accordingly.
In the example I gave at the beginning of this article, we chose to time our departure around 11:30 a.m. so that we would ride the ebb (drop in water) north out of Seattle to Port Townsend. With the current flowing north and the wind coming out of the south, we enjoyed a speedy, relatively smooth downwind sail to Port Townsend. At times, our speed over ground reached 10 knots, which is why we were able to get our destination more quickly than our hull speed would indicate.
For another trip north, we opted to leave during the tail-end of the flood. Why? Because the current in the central part of Puget Sound is relatively weak and wouldn’t affect our boat speed much. Plus, we were aiming to get to Mystery Bay before low tide. The charted depths near the entrance to Kilsut Harbor get quite shallow, barely over a fathom (6 feet) in spots. We draw 6.5 feet and didn’t want to risk running aground.
You can find tide and current predictions on NOAA Tides & Currents or DeepZoom with a quick search on your phone, but we still keep a current copy of the printed Ports and Passes on our boat. The beauty of a paper resource is we never need a cell signal to read it. The book also kindly explains how to read the predictions, how best to use them and includes local knowledge about particularly tricky or turbulent passes in the Salish Sea.
I’ve read about the PNW Current Atlas app, but have not used it. If you have, let us know what you think of it.
Understanding tide predictions
Tide predictions give the vertical height of the tide above or below the charted depth of a particular area. For example, if Ports and Passes predicts the high water for a specific area on the day you arrive will be 13 feet, the total predicted depth would be the charted depth plus 13 feet. Similarly, if the predicted low water is 1.3 feet, it would be the charted depth plus 1.3 feet. (And yes, in the case of a minus tide, such as -1.3 feet, you would subtract that from the charted depth.)
Why is it important to know this? It can affect how much anchor chain you need to put out and whether you will risk running aground in shallow spot. I’ve heard of more than a few sailors who have hit bottom even while tied up to a Washington State Marine Park mooring ball.
Understanding current predictions
Current predictions give the max speed of the current during flood or ebb (represented as +/-) as well as when to expect slack.
It’s important to consider which direction you want to go and which direction the water is flowing when evaluating these current predictions. Here’s our local example: In Puget Sound, you generally want to ride to the flood south and the ebb north. On the other side of the Strait, in the San Juans, you generally want to ride the ebb south and the flood north.
And don’t forget the weather!
In addition to minding tides and currents, note where the wind is coming from and where there are known tide rips along your journey. Wind against current can result in large, short and steep waves that aren’t much fun to sail through.
This recently happened when we departed Port Townsend in time to ride the flood south to Seattle and were greeted with 25+ knots of southerly wind right on the nose. With wind opposing current, we slogged our way through confused seas and at times saw our speed over ground drop to 3.5 knots. Our trip was slower than we were expecting and rather uncomfortable.
That’s the thing about sailing, though; you can’t control everything. But timing your voyage with tides and currents in mind certainly helps.
That’s amazing! What a wonderful lesson!
There’s dry dirt all around us. A little water sounds nice about now.
Love your blog! You make it fun and interesting and although I get seasick just thinking about boats, I love to read all about your life.
Thank you for this! Super helpful for new sailors!