Tide Tables and dive time determination

Hello,
I recently moved to Washington state and have some questions regarding proper determination of safe dive times in relation to tide charts. Can someone explain to me if it is better to begin a dive at high, low, or slack tides?

I am fairly new to ocean diving and would like do a few shore dives in my area in relatively shallow waters (45 ft). I was told by a dive shop that the best time to shore dive in admiralty inlet is 6:00 p.m. (on the 13th of Sept 2009). I understand that this is probably great advice, but I have a hard time believing that this is the only time available to do a safe dive in this particular spot. Is there a way I can use a tide table or tide chart to determine the safest times to do the dive so I'm not swept to Canada by currents? I have heard that the currents can be very dangerous in this area if you do not pay attention to the tide.

Thanks for any help

I can help you if you'll tell me what dive site you are talking about. More than likely the short answer is you need to dive a current intensive site at slack current.

Give me the dive site and I'll answer more fully. By the way neither slack nor high or low tide are at 6pm at Admiralty Inlet on the 13th.

I assume that you are probably in Port Townsend but I need more info.

There is no "good" answer to this question except, "It depends." The sites here are either current influenced or not and if they are not (for example, the "Alki Coves") then the only question is whether you want to walk on the rocks at low tide. The current dependent sites are REALLY a "depends" issue -- some you dive only at slack, some at slack or a flood, some at slack or ebb -- It Depends.

This is a case where "taking a class" may be a big help -- either a class such as run by Mischi (sp?) Carter in Seattle (Pelagic Scuba) or one of the many Power Squadron (boat) classes on tides and currents which will tell you a lot about, well, tides and currents!

Good question and good luck.

Spitaxe, there are two sites I always try to use together on the Oregon coast. The first is mobilegeographics.com:81/locations/1816.html which does a really good job of tide tables, and the second is swellinfo.com/surf-forecast/florence-oregon.html which is designed for surfers but tells you what the water conditions are. We tend to dive the jettys on high slack, but by using the surf table also you get a good idea what the surface conditions will be like. One lesson I learned the hard way is to make sure you are looking at the right tide table. The entrance of the Siuslaw River (above) and the Siuslaw River tables can differ by as much as 50 minutes!

When you are inland like Puget Sound as opposed to being on the coast the tide tables aren't enough. On the coast the tides and currents occur more or less together. But being 90 miles inland this doesn't work...that's why you need to look at current reporting stations.

Here is my general advice regardless of what site you are interested in...

Here is Puget Sound we have dive planning concerns that include current predicting. We are 90 miles inland so unlike at the outer coast tides and currents do not coincide due to the long distance from the coast and the many hundreds of miles of coastline that the moving water has to deal with.

A good start to a dive plan is to consider the size of the exchange...the difference between high and low tide. A low exchange will equate to more time at slack and a less drastic run up to max current than occurs with a high exchange.

A high exchange day would probably be in the 10 foot range meaning a 10 foot difference between high and low tide. A medium exchange may be a 6 foot difference and a low exchange might be in the 2 or 3 foot range.

You can get tide and current info on-line at many places but I generally use:

http://tbone.biol.sc.edu/tide/sites_uswest.html

Pick a location close to your intended dive site and if your site is current intensive look for the word "current" in the reporting station title. If it doesn't say "current" then the data reported is for tides only.

For currents you are generally looking for slack before ebb or slack before flood. FYI - tides describe the up and down movement of the water and currents describe the back and forth movement of the water.

As a general rule you probably want to get in the water 30 minutes before slack however if the prior exchange was large and the currents strong and the coming exchange is mild then you may want to get in right before slack.

In our area most people have the book, "North West Shore Dives", and use site specific current corrections that are included in that book. You will see the nearest current reporting station listed and then a correction + or - for the reporting station that seem to work for that specific dive site.

Most dive shops carry this book. The first section of this book also includes some information about dive planning regarding tides and currents.

You can play with the settings at the link above and can determine what the currents will be like at any given point in time so you can see what the currents are likely to be by the end of your dive.

In a nutshell, this is what you need to know to dive in the PNW and specifically in the Seattle/Puget Sound area. There are more specific details for certain dive sites and it's always a good idea to get local knowledge for any of the more challenging sites. It's also good to understand these things yourself so that you have a way of judging just how good that local knowledge or advice being given to you is!

Thanks for all the great advice everyone!!