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Old 14-02-2015, 10:13   #16
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Re: How Do I Use Slack Tide?

There is no such thing as slack tide.

Tides go up & down. Currents are directional.

Any tide & current book show:

Tides: high, low, high, low

Currents: flood, slack, ebb, slack, flood, etc.

You might want to get these straight in your own mind first.

Good discussion, though.
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Old 14-02-2015, 10:19   #17
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Re: How Do I Use Slack Tide?

As others have said, tide flow is slack at dead high tide and dead low tide. I don't worry about tide flow coming into my slip in San Pedro, CA as there is a negligible flow at any time. Low tide can be significant if you have to cross shallows to get to your slip as I had to do in Mystic Ct. I find wind to be a much more significant factor in entering my slip and for that reason I always like a slip that brings me into the wind, much the way a plane lands into the wind. This gives you a lot more control as well as an assist in deceleration. Where I have found slack tide to be very important is when you are going through narrow waters between two larger bodies of water. e.g. Woods Hole on Cape Cod and Hell's gate in NYC. You get hydraulic currents that can be very dangerous and difficult to navigate. Entering at slack low will give you minimal current and water flow from the stern to assist you through. I have been racing off of Plum Island in Long Island Sound doing 6.5 knots on my knot meter and sailing negative 3knots SOG. I trust this is helpful.
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Old 14-02-2015, 10:34   #18
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Re: How Do I Use Slack Tide?

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Originally Posted by Bobby Wandering View Post
I guess I should have been more specific. How can I use the slack tide, slack water, to my advantage as I leave and return to the dock? Does this information apply more to the docking and leaving or to the actual voyage itself?
It's purely situational and you need to analyze your circumstances with respect to current/tide and make decisions based on that. The impact of current and tide varies depending on what you're trying to do and where you're trying to do it.

You're probably not going to wait for slack water at your dock for departing or arriving. Instead, you'll modify your docking procedure to either take advantage of a favorable current (let it carry you to the dock) or to deal with a foul current (spring lines, etc). There are plenty of tutorials on how to do that in various situations.

As Atoll pointed out, there are some places where slack water is highly advantageous, particularly in passages through narrows, inlets, and other spots where the ability to maneuver is limited. Again, it's situational.
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Old 14-02-2015, 10:38   #19
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Re: How Do I Use Slack Tide?

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Originally Posted by Stu Jackson View Post
There is no such thing as slack tide.

Tides go up & down. Currents are directional.

Any tide & current book show:

Tides: high, low, high, low

Currents: flood, slack, ebb, slack, flood, etc.

You might want to get these straight in your own mind first.

Good discussion, though.
Then there is getting the "hang" of the slang....which doesn't mean a pause or being suspended from above.

There is some apparent pause in the up and down as the forces reverse because the tides slow and stop as they change direction. The rule of 12 is handy for guesstimating currents and tide height.
Up to 1/6 of the time after the tide change 1/12 of the water will flow.
up to 2/6 of the time 2/12 more of the water will move.
up to 3/6 3/12
4/6 3/12
5/6 2/12
5/6 1/12
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Old 14-02-2015, 10:41   #20
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Re: How Do I Use Slack Tide?

The geography of New York Harbor with it's various bays, islands, and tidal straits produces some interesting tidal currents where the Hudson River, Long Island Sound, and the Atlantic Ocean all converge.

Slack water associated with the changing of direction of tidal currents at The Battery does not occur at the extreme high and low tides measured at The Battery as one might expect, but in fact occurs two hours after.
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Old 14-02-2015, 10:54   #21
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Re: How Do I Use Slack Tide?

Here's a good tidal chart book for Puget Sound waters. It's similar to the older Washburn book.

http://www.amazon.com/Tidal-Currents.../dp/0914025163

The apps for your phone are excellent as well for the Sound, San Juans and Gulf Islands. Further north into B.C. waters, there is a good tidal book available as well--google it--several sources for it.

There are places where the tidal time chart says it's slack tide, but what you actually experience in that hour is heavy current with whirlpools, rips, etc., and 8 or 10 kts of current. On a keel boat, you can have a 90 degree turn happen in a second in these conditions no matter how fast you are making way.

In some of the tighter spots in the PNW waters, you may have 'overfalls'. those are a force certainly to reckon with--better to avoid altogether.
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Old 14-02-2015, 14:03   #22
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Re: How Do I Use Slack Tide?

You all have written some good posts.

However, the OP, Bobby Wandering, refined his request for information via his 2nd post. He asked that we give him information on how to use the tide and current in docking his boat.

Maybe he needs to take a handful of sawdust or bread crumbs and toss it on the water to see what is happening at various tidal states. Maybe he wants to calculate the best time for docking when he gets back?

Ann
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Old 14-02-2015, 14:23   #23
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Re: How Do I Use Slack Tide?

Newt can correct me on this, but I think Crossing out over the Columbia Bar the premo time is a window 30 minutes either side of High Slack, second best is low slack, ugly is tide coming in...
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Old 14-02-2015, 14:45   #24
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Re: How Do I Use Slack Tide?

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Originally Posted by Ann T. Cate View Post
You all have written some good posts.

However, the OP, Bobby Wandering, refined his request for information via his 2nd post. He asked that we give him information on how to use the tide and current in docking his boat.

Maybe he needs to take a handful of sawdust or bread crumbs and toss it on the water to see what is happening at various tidal states. Maybe he wants to calculate the best time for docking when he gets back?

Ann
Great point Ann... tide meeting river current effects my marina docking condition considerably... BTW our ducks prefer breadcrumbs over sawdust ...so after a couple rookie close calls I started practicing dock n departures in a sparsely populated section of our marina. Yes people looked at me like I had rocks in my head and some asked if I needed help, but now I know how Sedna will react to different conditions. Each boat seems unique in how wind, and current effect maneuverability in close quarters.
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Old 14-02-2015, 15:20   #25
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Re: How Do I Use Slack Tide?

Inside Marina De La Paz where I keep my boat, we experience currents from the rising and dropping tides. Folks around here use the slack tides to spin their boats around using lines. With a few friends, they back out of the slip, apply force with lines on various points of the boat, spin it, and bring it back into the slip stern first. Easy at slack tide, nearly impossible when the currents are running.

Cheers, Bill
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Old 14-02-2015, 16:38   #26
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Re: How Do I Use Slack Tide?

To get through the passes north of Desolation Sound you need to be aware to the time of the turn (aka "slack tide).

I wrote this for another sailing forum to show how to get into the Broughtons from the Salish Sea.

SailNet Community - View Single Post - North to the Broughtons
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Old 14-02-2015, 17:11   #27
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Re: How Do I Use Slack Tide?

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Sorry Atoll,
Here in the PNW slackwater is said to mean Low tide or high tide. In the Salish sea they are often not even close. That was the point I was trying to make.
That is highly non-standard usage. The more usual definition is given in Bowditch:
Quote:
Slack water. The state of a tidal current when its speed is near zero, especially the moment when a reversing current changes direction and its speed is zero.
This is consistent with Atoll's interpretation.
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Old 14-02-2015, 20:04   #28
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Re: How Do I Use Slack Tide?

To your original question. I moor at Tyee and find the current speed not noticable for docking. It would be different docking in the Narrows at good flow but the water in and out of Commencment Bay never moves fast enough to cause a problem.

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Old 14-02-2015, 20:51   #29
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Re: How Do I Use Slack Tide?

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Originally Posted by Ziggy View Post
That is highly non-standard usage. The more usual definition is given in Bowditch:


This is consistent with Atoll's interpretation.
I'm from the PNW and I've only ever heard it used in the Bowditch sense.

You go through the passes at slack. Slack is not at the same time as HW or LW.

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Old 14-02-2015, 21:02   #30
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Re: How Do I Use Slack Tide?

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As others have said, tide flow is slack at dead high tide and dead low tide. I don't worry about tide flow coming into my slip in..............
This may be true somewhere, but it sure isn't in San Francisco Bay. There is up to an hour difference. Look it up. Please.

Tide doesn't flow into anything, current does.

Doesn't matter whether you're trying to dock or to move your boat somewhere.

Also, the rules of twelfths is for tidal height, not currents.
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