Slack Tide?

[MXGratefulDiver]

Tacoma Washington where the currents seem to be a real concern.

What y'all are calling slack tide is really a misnomer. You mean to say "slack current". This can happen either before or after the actual turn of the tide, depending on how currents flow in the area you're talking about. It's not a simple thing to predict.

Tides are water movement up and down. Current is water movement side-to-side. The latter is affected by the former, but it's also affected by the bottom topography and how the shoreline affects water movement (e.g. eddies, reversals, etc).

For example, on the north shore of Seattle there are two dive sites in Edmonds ... the Oil Dock and the Underwater Park. They're only about a mile away from each other ... but the topography and the interaction of opposing currents mean that slack before flood can be as much as an hour and a half different from one site to the other.

Tonaskai ... I work in Tacoma and live nearby. Let's go diving sometime and I'll talk to you about how it works at some of our local dive sites.

... Bob (Grateful Diver)

 

[MXGratefulDiver]

Well, this is topical. I was on my way home from work and stopped by my local LDS. Ran into Stephen Fischnaller ... he wrote our local shore diving "bible" ... "Northwest Shore Dives". He also gives seminars in planning dives around tides and currents.

You can get some very useful information from his website ... http://www.bio-marine.com/ ... and if you are interested in his classes they're fairly inexpensive (less than $50) and very comprehensive.

He was in the process of setting up a class for June. If you're interested, drop me a PM and I'll give you the specifics.

... Bob (Grateful Diver)

 

[String]

We call it "Slack Water" over here as opposed Slack Tide which is probably more descriptive.

Slack Water is that mythical 45 mins or so of no current where its nice to dive. Mythical because we never EVER seem to be at the dive site at the required time so dont get it

As someone else stated, even near-by sites can have drastically different slack water times and durations.

 

[lamont]

is the best time on a slack current following a flood current? and does a fairly vigorous flood current beforehand help?

 

[MXGratefulDiver]

is the best time on a slack current following a flood current? and does a fairly vigorous flood current beforehand help?

The answer to your first question is that it depends on the site. Again ... citing local dive sites as examples (since you live around here) ... if you were diving Edmonds Oil Dock the answer is no, if you were diving Three Tree North the answe is yes, if you were diving Sunrise the answer would depend on how much water movement (determined by the size of the tidal exchange) was present that day.

The answer to your second question is "rarely". Often a vigourous flood only means that during slack the water will not actually stop at all ... it will only swirl around till it settles in a new (for the ebb) direction.

Not to sound like a salesman, but for those of us living in Pugetropolis, Northwest Shore Dives is an excellent source for this kind of info. I highly recommend it (and Fischnaller's course as well).

... Bob (Grateful Diver)

 

[pasley]

Tides, an interesting subject to be sure. Useless factoid: Not all places on earth have the same number of tides and there are even places that have virtually no tide at all! The Mediterranean Sea for example has virtually no tide and areas near the equator have little tide if any.
http://www.co.beaufort.sc.us/bftlib/tides.htm
http://www.seafriends.org.nz/oceano/tides.htm

So diving in Panama where the average tide is about 1 foot slack tide is not a real issue. But in Canada in one port the extreame high tide recorded is 15.8 meters or 51 Feet! Now that is a tide and diving a slack tide is a must. http://atlas.gc.ca/site/english/facts/tides.html#table

 

[H2Andy]

hmmm.... never thought about that...

so why is it that at the Equator you have such little tide, and yet at the poles
(at least in the northern half of the world) you have such huge tides?

since the moon affects the tides, it must be that that gravitational pull of the moon
is not as strong at the Equator.... or something....

anyone know?

 

[String]

Ideally in havens and areas where rivers run into the sea you would expect to get the best visibility on the flood/high water and less on the reverse due to the silt etc from rivers being carried into your area.

However as mentioned site selection changes this most, some dont have proper slack on one part of the tide whereas others you get longer on one rather than the other.

Its a near impossible thing to predict and local knowledge of when slack is on common sites is the best idea.

Got a 7.2m tidal range here today. If i can dive on the weekend its still going to be large. One of the downsides of diving here.