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I have done a search of the forum and havn't found much, maybe I'm just using the wrong key words, so please forgive me if this is the case.
I am wondering if anyone can point me at any basic information not only about reading tide charts, but more what to look for when planning a dive. This wasn't really covered in the OW cert.
I mean I can make some assumptions about what to look for and when to dive, but I don't think this is something one would want to make a mistake on.
Looking to become more self sufficient. Any help is as always appreciated.
The short answer is that tide and current (where available) tables will give you a rough understanding of the timing and magnitude of water movements. The effect it has on diving is VERY location specific. Your best bet is to talk to other divers and your LDS about the sites you would like to dive.
Without exception at every LDS that I've asked about diving a current sensitive site, they've quickly pulled out the tables or computer to give me very specific advice on the best time to go.
Here are a couple thread on the subject that I've previously participated in, I'm sure there are more threads out there too.
What one person/place calls bad, another may call average. There is no simple answer to your question.
Tides have almost no impact when boat diving. The only thing to consider is that the object you are looking for may be at a slightly different depth. Where this is an issue is when you want to go see that thing that is at 125 fsw when at low tide, but it's now high tide and below the NDL. (Plus boat captains have to deal with underwater hazards when navigating, particularly at low tide.)
Some things to consider when shore diving: Water movement is greatest between high and low tides. At both high tide and low tide, the water movement is less. Less movement, less difficulty entering and exiting. Personally, I don't see enough of a difference to concern me. I like high tide because I don't have to walk down the beach as far. I will go in at any tide point.
Tides are a form of swell. They are called forced swells with a 12 hour cycle (approx.)
I like morning dives around here. The wind hasn't pushed against the water surface enough to add that extra issue to entry/exit. Wind on the water surface adds choppy water surfaces. It's not as much fun as swimming on a glass surface.
What I pay more attention to is the swell reports. I want to know how tall they are and how far apart they are. The more time between swells, the deeper the swell can be felt. When shore diving, I like swells that come in close to each other. How much is close? That is where each diver has to determine what they consider normal. A formula I use for myself is: If the distance between waves times 2 is more than the depth I want to dive, it is likely to be pretty rough at depth. It's a rough estimate only. It is influenced by the height of the waves. There may be a huge space between wave crests, but if the wave height is measured in inches, then I don't care.
Let me give this a shot.
Reading a tide chart is simple enough; there are locations, dates, times and measurements above and below average sea height. This information can assist you in planning your entry and exit points at a dive site on or near the location you choose.
When planning a dive, you can use the outgoing tide to assist you in transporting you to a dive location. Perform your dive during the slack time, the time when the water is not moving towards either high or low tide. As the tide begins to move in, flood tide, you can use this water movement to assist you to your exit point. Your exit point may or may not be where your entry point was. This depends on the effect of the waterline on these points and the safety with which you can enter or exit from these points.
The effect of tides are different for each location you will choose to dive. Ingoing or outgoing tides can create strong currents, dangerous shore break, and turbulent seas.
Depending on the topography of the ocean floor, currents can be created which are very strong or not. Remember, if a large volume of water is passing through a channel the rate at which the water must travel increases as the channel narrows. If you choose your entry or exit at the wrong times you may find it difficult to arrive at your exit point.
A rising tide in association with even an average surge can create quite a situation at the shore. This higher than average volume of water can effect how you enter and exit the water and how it effects your movement on the shore.
Changes in tides can effect the ocean surface by creating some chop that could create a rocking situation on a boat or flotation device, making entry and exit a chore.
Currents at depth, created by tidal movement, can place you somewhere you hadn't planned, if you don't pay attention.
Hopefully, this will at get you thinking about other ways that tides can effect your dive.
In my opinion, learning about oceanography is something that every diver should pursue.
I am wondering if anyone can point me at any basic information not only about reading tide charts, but more what to look for when planning a dive. This wasn't really covered in the OW cert.
Although the local diving here is mainly in the North Atlantic, divers also dive in the Bay of Fundy (which has the largest tides in the world). Subsequently, I include tide tables into my OW program and students must pass a separate exam on them. You can predict fairly accurately the tides/currents that will be present when planning your dive, at any point in-time. Most tide charts that I've used have an area in them that explains how they work; so it's a matter of going through the exercise of learning how to use them. If you run into difficulty, a local instructor should be able to help you. Good luck!
Thanks for all the input folks. DCBC: Makes sense that you would have to include some instruction on that in your neck of the woods - pretty big issue there!
Thanks for all the input folks. DCBC: Makes sense that you would have to include some instruction on that in your neck of the woods - pretty big issue there!
As a matter of interest, each day 100 billion tons of seawater flows in and out of the Bay of Fundy during one tide cycle. This is more than the combined flow of the worlds freshwater rivers!
Depending upon location, the tides can change by 8 feet in an hour. That's a lot of current if you get it wrong.
As was said many times in this thread...tides and currents are very site (location) dependent. Local divers are your best resource. I wouldn't rely on only having a tide table and a great understanding of how to read it to keep you safe.
If you head out in my local area with a boat and don't have a good local knowledge of how the current effects the passage...there's a good chance you be coming back. Upwelling and down welling are huge and will take you for a ride you wont forget.
Tides can have a MASSIVE impact boat diving in some areas of the world. If its a small boat launched from shore they can dictate whether you can launch or whether you can recover (ie is the slip wet or dry). In the SW UK the range is over 7m from high tide to low tide so can make a substantial difference to dive and decompression planning in the matter of a few hours. The large tidal ranges can also mean very strong tidal currents meaning slack water times are short lived and you have to arrive EXACTLY on time.
Yes in some areas of the world tides aren't that important but they're the first and most important part of dive planning in other areas.
Predictions however are VERY location dependent - even 2 sites within a mile can have vastly different high/low and slack water times and durations depending on coastline, bottom topography and so on. Tidal diamonds arent that useful - even if there is a charted one near a site those above variations can make the difference of a few hours either way over a very short distance.
If you get printed tide charts the output will be similar with a couple exceptions:
1) Probably no moon/sun times
2) This online chart is corrected for daylight savings time. Many printed charts are not. The chart will include a note saying whether or not the corrections have been applied.
At 3:15 this morning the water should reach a maximum of 13.73ft.
At 9:30 a low of 10.04 ft. should be reached. That makes for an ebb of ~3.7ft. Very small for this site, but average to large in some other locations.
By 1:40 the tide will again rise to 11.34ft. That is a tiny (by local standards) exchange of only about 1.25ft total.
The cycle continues and at 8:30 tonight a new low of 6.33ft should be reached. An exchange of ~5ft, still small by local standards.
The cycle completes with a high at 3:50 tomorrow morning at 13.65ft. A flood of ~7.3 ft. Medium by local standards.
Through experience and talking with local divers I know that all the common Vancouver dive sites will have only minor currents, and I wouldn't worry about current at any of them at any time today. But there is nothing directly in the tables to tell you that.
It's worth noting all these numbers are approximate predictions. If you look at the DFO website you'll find slightly different times and heights predicted. The predictions only really apply in the immediate vicinity of the tide station. Divers/guide books/LDS can often provide corrections for sites that are far from a tide station.
Typically one would combine this info with a chart showing the flow direction. In many locations the direction of flood and ebb is obvious though on complicated coast lines with many islands/inlets/rivers the directions may not be obvious.
Again printed current tables often have a couple differences
1) Ebb/Flood are probably only indicated by positive or negative numbers no words.
2) Just like tide tables, current tables are often not corrected for daylight savings time.
Sechelt Rapids, British Columbia Current (use with caution)
8 April 2010 - 9 April 2010
49.7383° N, 123.8983° W
Sechelt Rapids (Skookumchuck) is located about 40 miles NNW of Pt. Atkinson as the crow flies, or about 60 miles over the water. The predictions are for the same day. The height and time of the tides in both locations are similar, but it is obvious from the start that the current situation is very different.
This chart is pretty straight forward to read, and it starts off with over 11knots of current. You'd have to be one crazy cowboy to want to ride that current. Around 2 knots max flood makes today one of the few good days to dive the Skook. I'd probably try to be there around 10:15 to watch the water and splash as it slows down.
This current table really only applys to a very small stretch of water half a mile either side of the current station and the current is much slower. But if you want to dive or boat in an area that can run 16+knots you REALLY want to know what the current is going to do.
Here is a video of what happened when a tug boat captain got it wrong in the Skook.
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