Tides and Diving

[akirawut]

sschlesi: Thanks for the detailed breakdown - that gives me a good idea of what to look at and what to look for.

Definitely have to stick with the getting information from the locals and combining that with the tide tables.

 

[Sas]

Tides have almost no impact when boat diving.

Hmm, maybe not where you are but it would be wrong to assume this about other places. Tides have a HUGE impact on boat diving where I am. Slackwater only occurs at certain periods and if you want to have a dive that doesn't involve drifting in 7 knot tides, then you have to plan to dive at slack. A shot is dropped in and we sit on the boat and wait til it shows that it is slack then do the dive. Also the heads of the bay that I dive in mostly is quite dangerous and there are shipping channels. Some dive sites can only be done on flood tides and others on ebb tides.

Also in some places tide movement can cause a big difference in depth so you do need to know what tide you'll be diving so you can use the right gas and plan your dive accordingly.

For shore dives, most sites near to me are better done at high tide as the water is cleaner and it's also a bit deeper. There are some though that have to be done at low tide as there are shallow rock platforms that become exposed that are only safely crossed when out of the water. At these sites swells that are far apart are also more ideal too, otherwise it can be very ugly underneath.

Pretty much everything about tides is so location dependent it would be best to talk to locals and start recording what sites are better at what tides. I have done this for each dive and find it much easier for planning now as I know what tide to dive things in.

 

[samaka]

If it's currents and how to dive in waters with currents you can have a look at my website where I explain those things in easy words. This is Egyptian waters but current is current and this should help some anyway.

DIVING FROM LIVEABOARDS IN EGYPT

Hope you like it and find it useful.
.......a.......

 

[spectrum]

If you are up in the tidal section of a river or estuary the actual high and low times can have a very significant offset from the published ocean tides. Sites such as this one can let you drill down a little closer than most published tide tables.

 

[miketsp]

Local knowledge is very important. Often there is no easy direct relation between the phase of the tide and the current that is running.

As for the worst I ever encountered, about 35 years ago I had to do a feasibility study for a cable laying operation in the Straight of Magellan & we did an on site survey.

An extract from recent literature reads:
The Strait of Magellan is a 500 km long navigational waterway connecting the South Atlantic and South Pacific oceans. On the Atlantic side, the Strait is characterized by semi-diurnal macro-tides with mean and spring tide ranges of 7.1 and 9.0 m, respectively. On the Pacific side, tides are mixed, mainly semi-diurnal, with mean and spring tide ranges of 1.1 and 1.2 m, respectively. Wide tidal flats and basin geometry tend to amplify the Atlantic shelf tides in the eastern extreme of the Strait. Tidal choking occurs in a series of narrows, causing stepwise decreases in tidal range from east to west. The mean tide range is initially amplified to 8.4 m, then reduced to 4.0 m, and subsequently to 1.2 m within 150 km of the Atlantic Ocean. Peak tidal currents exceed 3 m s−1 in the narrow constrictions and may reach 4.5 m s−1. The tidal form number is 0.12 in the eastern Strait, but exceeds 0.25 less than 125 km from the Atlantic. Bahia Gente Grande, an embayment located 165 km into the Strait from the Atlantic, experiences a tidal regime that shifts from semi-diurnal to third-diurnal to quarter-diurnal during each month. This regime results from reduction of semi-diurnal constituent amplitudes, existence of appreciable diurnal constituent amplitudes, and a four-fold amplification of the M6 amplitude, which in combination give rise to the double water phenomenon.

For the imperial measures guys, 9m is just under 30ft!
4.5 m s-1 is 8.75knots or 10mph.

 

[AfterDark]

In my gear bag in a zip lock bag I carry a tide chart booklet for RI where I do 95% of my diving.
$1.00 at West Marine. I use the tides to carry me to and from dive sites when I can. I try to dive the incoming tide (I'd rather coast on the way back) in general. I dive a channel with a 5 knot current at its peak. I dive the slack starting just before the incoming is done, drifting into the channel then later drifting back out to where I started. During that time a interesting thing happens, I get to a point where surface water is still coming in but the deeper water is going out. When I get back to where I started I surface into the still incoming water and drift back into the channel, descend and repeat until the ride stops. Definitely get some local advise and spent sometime watching the water where you dive (when your not diving) you can learn a lot by watching. Also samaka's link is a very good place to start.

 

[Capt.Ed]

Everybody has already covered current pretty thoroughly but there are a couple of other factors to keep in mind as well...WIND. I live on the Gulf Coast of Florida and there are days when we're predicted to have a two foot tide drop and we actually see the tide rise an extra 6-12 inches in the bays and rivers. Why? Because there a 15 knot wind is blowing from the west and it pushes the outgoing tide back inshore and the bays and rivers "fill up". And the opposite can occur too. A 15 knot wind out of the east may push all of the water out of the backcountry and create really crappy conditions (visibility wise) offshore, not to mention drop the tide level significantly lower than predicted.
Basically what happens is that the wind can push the water into an area and it can also push the water out of an area. Of course anytime wind is involved it will likely lower visibility as well which can make diving less enjoyable.
Just one more variable to consider. If you're several miles offshore it won't matter, if you're diving close to shore or in a bay or inlet it's one more thing to think about.

 

[Aquabear]

I am also looking to learn to shore dive here on Long Island and will look to join a local group with experience in diving the slack tide- especially at Ponoquogue Bridge. Been researching alot but will not try to EvilKenieval it out on my own.