Predicting Slack Tide

[Darnold9999]

To expand a bit on what others have said. Currents are not as easy to predict as tides - particularly around here where tides are moving large volumes of water in and around very large obsticles (islands). Tides and currents are quite predictable on the outer coast, but less and less so as you move into Puget Sound and into the waters among the Gulf Islands and the islands midway along the east coast of Vancouver Island where the tide floods in from two opposite directions and meets in the middle.

 

[String]

Isn't that physically impossible? Tide goes in, tide goes out. Current slows to zero, before reversing and picking up speed again. "Slack" is, perhaps, in the eye of the beholder with even small tidal movement not considered "slack."

Its certainly possible. With some channels or basins the slack water is when the height inside equals the height outside which isnt always the same as local high or low water. The difference can be several hours.

 

[Coldwater_Canuck]

Thanks for all your replies, this really does seem to be a fairly complicated subject.

 

[gzscuba]

I moved to the Seattle area a couple of years ago and it was a bit of culture shock learning to dive with the Puget Sound currents. I took a tides/current class through Underwater Sports. They've got a tides/currents book from Pelagia Scuba (Pelagia Scuba) that really helps with the dive planning. The class complements the book. You might be able to figure out things with just the book (since I don't see any classes scheduled for the near future.

The cliff-notes version is that you get a current table (like the tides/currents book) that predicts the time of slack current for some NOAA standard spots. Then, for each dive site, you've got a correction factor that you add to the time of slack current that tells you about when the slack is for that site.

Hope this helps a bit.

 

[flw]

Isn't that physically impossible? Tide goes in, tide goes out. Current slows to zero, before reversing and picking up speed again. "Slack" is, perhaps, in the eye of the beholder with even small tidal movement not considered "slack."

Depends on where you are - I live by the Pentland Firth at the north end of Scotland, where the N sea is to the east,the Atlantic to the west and the various islands of Orkney are to the N( plus assorted isles/skerries inbetween) - the tide times for the Atlantic and N Sea are different,and there is the added influence of Scapa Flow filling and emptying through various channels - there are defintely places locally where the water never stops moving-it might swing round and the eddy take you NW on an Eastbound floodtide as it does off Swona, but it won't stop moving.
Slack doesn't necessarily coicide with either low or high water-and sometimes the longest slack water is actually on the biggest springs
--The weather has an effect as well,pushing the water either east or west.