Rapids question: slack tide vs slack current - SailNet Community

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Old 08-20-2007
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Rapids question: slack tide vs slack current

I sail around the Pacific Northwest in Canada and have been contimplating passing through different rapids as there are many around here like Dodd Narrows, Seymour Narrows, etc. My big question is this: Why is it that all the books tell you to pass through at slack tide, but NONE of them tell you that slack current is completely different than slack tide? When I was sailing this last month I met a women who told me that there is a big difference in slack tide and slack current that I should be aware of if I'm going to pass through any rapid areas. She advised me to get a different book other then the tide and current tables book that I had which I did, but unfortunately I don't have it with me to tell you the exact book title. Anyway, long story shorter, this new book I got taught me a whole new time to go through the rapids which was WAY different by at least three hours then the tide and current book that I was using. I finally figured out that if you plan on going through the narrows you should do it about 2 hours or so before the slack tide to get the perfect slack current. This was a big surprise because I had never seen anything written explaining the phenonoma before. Am I correct or am I still lost and venturing into dangerous waters?
I will get back to this forum with the correct book titles soon.
thank you
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Old 08-21-2007
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I cruise the same waters and I've been using current tables and tide tables for a couple of decades and frankly, I don't know what you're talking about when you say there is a three hour difference between the perfect slack water and the predicted slack water.

I hear several boaters use the term "Slack tide" and "slack water" interchangeably. The predicted times for low or high tide are not the same for the predicted slack waters at passes. The slack water prediction for passes are generally in a different section of the tide book. Deception Pass is right in my back yard. This morning's slack water before flood was at 3:25am. The low tide in La Conner was at 6:21 am. I've found that both predictions are very accurate.

So anyway, there are several reference books and tide/current programs that accurately predict slack water at "narrows" and "channels". It's safe to navigate those water around the time of the predicted slack. It's also not reckless to go through when the current is running if you understand how the current and back eddies will affect your boat. When we're sailing our local waters, we regularly plan our trip back home on a Rosario ebb heading south and then catch the Deception Pass Flood to get squirted back into Skagit Bay. We've seen 12 to 13 knots on the GPS which is pretty exciting in a heavy displacement hull when going through Deception Pass with the current when it's running 6 to 7 knots.
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Old 08-21-2007
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slack tide vs slack current response

Thanks for the response. Your comments basically confirmed my concerns were justified. Slack tide and slack current are deffinately NOT the same. Which is nice to know before attempting passage through any narrows.
It just seems odd to me that this basic, most valuable, and most neccessary knowledge is not made more available in all the literature on this subject found on the internet or in books.
The book I was referring to in my previous thread on this topic, the one that finally showed me the true differences between slack and max currents at different narrows from Olympia, WA to Prince Rupert, BC is "Ports and Passes 2007" published by Chyna Sea Ventures Ltd.
My latest experience occured when I was in Nanaimo on Aug 12, 2007 planning passage through Dodd Narrows (south) on an ebb tide. High tide in Nanaimo was at 4:40 AM, which previously would have been the time I would have attempted my passage. But my new currents book told me that Dodd Narrows was max slack going into an ebb at 3:51 AM (51 minutes earlier), which was the true ideal time to pass through Dodd Narrows heading south. In the end, we decided to abandon traversing Dodd Narrows in the dark and just crossed the Straight of Georgia for Point Roberts at 6 AM, which turned out to be the fastest route to Bellingham as we avoided all the Gulf and San Juan Islands and dealing with all those currents.
Anyway, thanks for the comment on this topic and I do hope this info helps somebody out there. I know it would have saved me a lot of head aches had I read this info two years ago. And I'm still wondering why it's not discussed more in other passages considering it's vital importance.
Good luck to all sailors passing all narrows.
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Old 08-24-2007
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There is a clip of us going through Malibu Rapids a few years (and boats) ago in this youtube video. It runs at 9 knots and gets your attention.

http://www.youtube.com/watch?v=DnjLgDt9-XI
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Old 08-24-2007
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That's a beautiful clip! My wife and i will be taking our boat up to the area next May for a couple of years. We've sailed the southern Gulf Islands and are relly looking forward to heading to the northern reaches.
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