When to plan a shore dive?

[grouchyturtle]

I know that typically you should plan to be in the water at slack high tide for a shore dive. Also depeding on a few different factors slack will last a different amount of time at any given location on a given day. Regardless of how long slack will be, though, the number on the tide table called high is the time of slack tide or at least the peak of slack tide.

So, say the table has slack listed as 8:30, for my location.

Do I:

A: want to get in the water at about 8:30
B: time it so I'm just getting out of the water at 8:30
C: time it so half of my dive is before 8:30 and half is after 8:30

 

[adshepard]

I know that typically you should plan to be in the water at slack high tide for a shore dive. Also depeding on a few different factors slack will last a different amount of time at any given location on a given day. Regardless of how long slack will be, though, the number on the tide table called high is the time of slack tide or at least the peak of slack tide.

So, say the table has slack listed as 8:30, for my location.

Do I:

A: want to get in the water at about 8:30
B: time it so I'm just getting out of the water at 8:30
C: time it so half of my dive is before 8:30 and half is after 8:30

Well it certainly depends on where you are shore diving. Shore diving in the Cape Ann area of Massachusetts generally does not require any worrying about slack tides. However when diving Eastport, Maine near the Bay of Fundy diving slack is of the utmost importance (wouldn't want a quick trip to Europe.)

Anyway I try and go with your option C. At low slack in Eastport I can hit the water over an hour before slack and get in two shore dives before things pick up. With high slack there is less time of "dead" water but the same theory works well.

DSDO

Alan

 

[Diver0001]

I know that typically you should plan to be in the water at slack high tide for a shore dive. Also depeding on a few different factors slack will last a different amount of time at any given location on a given day. Regardless of how long slack will be, though, the number on the tide table called high is the time of slack tide or at least the peak of slack tide.

So, say the table has slack listed as 8:30, for my location.

Do I:

A: want to get in the water at about 8:30
B: time it so I'm just getting out of the water at 8:30
C: time it so half of my dive is before 8:30 and half is after 8:30

It depends on the particular site and what your goal is for the dive. If the tidal current runs parallel to shore then it's often easy to go in just before slack. That way you can drift with the tide both before and after it changes and come out about where you started.

R..

 

[Scubaguy62]

Well it certainly depends on where you are shore diving. Shore diving in the Cape Ann area of Massachusetts generally does not require any worrying about slack tides. However when diving Eastport, Maine near the Bay of Fundy diving slack is of the utmost importance (wouldn't want a quick trip to Europe.)

Anyway I try and go with your option C. At low slack in Eastport I can hit the water over an hour before slack and get in two shore dives before things pick up. With high slack there is less time of "dead" water but the same theory works well.

DSDO

Alan

Right on!!

I usually plan to be in the water about 20 mins prior to slack high when the dive is to less than 20 feet, but if you're in the turks and caicos, where you have a wall 300 feet from shore, it makes no never mind.


Semper safe,

Rick

 

[matt_unique]

1/2 before and 1/2 after for the best conditions.

--Matt

 

[MXGratefulDiver]

I know that typically you should plan to be in the water at slack high tide for a shore dive. Also depeding on a few different factors slack will last a different amount of time at any given location on a given day. Regardless of how long slack will be, though, the number on the tide table called high is the time of slack tide or at least the peak of slack tide.

So, say the table has slack listed as 8:30, for my location.

Do I:

A: want to get in the water at about 8:30
B: time it so I'm just getting out of the water at 8:30
C: time it so half of my dive is before 8:30 and half is after 8:30

Well, first off ... you should be planning your dives using current tables, not tide tables. Tide tables are only good for giving you a general idea of whether a dive site is a good choice on a particular day.

Times of minimal current flow (or what most folks call "slack") typically occur some time after a high or low tide. How much time will depend on a number of factors ... the most important being the amount of tidal flow (larger tidal flows typically take longer to slow down than smaller ones), and the topography (is the site prone to "eddys" due to something like a jetty or a natural point). You can dive around slack before flood (the slack that occurs after a low tide) or slack before ebb (the slack that occurs after a high tide). Many sites will have stronger current for a flood than an ebb ... or vice versa ... that will make one slack period preferable to the other for diving.

Ideally, you want slack to occur about halfway through your dive. This is only really important for sites that are very current-sensitive, since you'll want the current to carry you in one direction for half the dive, then in the other direction for the other half. For dive sites that are not too current-sensitive, you can plan your dives anytime around the slack period, since the objective is to dive the site when the current is low enough that you don't have to work too hard ... and during the hour or so preceding slack to the hour or so following slack, most dive sites are quite diveable.

Also, keep in mind that both tide and current charts are based on predictions at a particular spot ... which may be some distance from where you are planning to dive. There are "corrections" that should be factored in between the closest measurement point (e.g. a buoy 2.3 NM east of Admiralty Inlet) and the dive site you are planning to dive (e.g. a few miles northeast of that buoy).

Finally ... keep in mind that there's a reason why they call 'em "predictions" ... the currents don't always do what the charts say they're supposed to.

... Bob (Grateful Diver)

 

[neil]

On top of all the good info from Bob and others, it's not a bad idea to seek out divers who dive that spot regularly and get the story. Since you're from NJ, here's an anecdote:
I read in a book about Shark River Inlet, down in Belmar. The book said hop in under the drawbridge about an hour before slack tide, and you get 15 minutes of slack. We drove down there, went into the local shop to say howdy and told the guy what we were going to do. He laughed and said, go down there an hour before slack toss a twig into the water and watch it. Then he said "15 minutes before and 15 after is safe, I mean it". Well, I tossed that twig in and it musta been moving at ten knots! At 15 before, we jumped in and went right to the bottom hanging onto rocks for dear life, our legs flying out in the breeze. After 15 minutes, right on time the water stopped moving and we had a very interesting time. A few minutes after the water started moving again we got the heck out!
I later met divers who go in sooner, but just decided they're crazy.
Neil

 

[MXGratefulDiver]

Yes, for current-sensitive spots local knowledge is invaluable.

We have a spot up here called Skyline ... it's on the end of a passage that funnels a lot of water between Puget Sound and the Straits of Juan de Fuca. It's best to dive 30 minutes prior to slack before ebb, as the flood current will push you from the entry toward the wall, then the ebb current will push you back where you started. Currents here are very strong, and common sense would tell you that the less tidal exchange you get the better off you'll be. Common knowledge says it's not a good idea to dive here on a day when there's a very small ebb exchange. When there's a very small exchange, the current never really changes direction ... it just slows down going west, then speeds back up again. Next stop, the southern end of Vancouver Island (hope you brought your passport and a phone card).

Current patterns at every site are unique, and are influenced not just by the tides, and not just by the topography of the site ... but also by the shape of the area through which the water enters and exits the site. It's often a complex pattern, sometimes causing currents to eddy and reverse in ways that do not show up on a chart.

As neil suggested, it's always a good idea to talk to people who dive there ...

... Bob (Grateful Diver)