Tide table

[noblesix]

Hi all, i have a question about dive practice. I was recently on a dive trip in Maldives and quite disappointed with one of the dive.

We were promised a "shark dive" at one of the channels with strong incoming current so we were quite excited. The dive operator always has a fixed dive schedule, always at the same time in the morning. The guide always jumps first to do "current check" and he climbs back to the boat and informs us about the current; incoming, outgoing, strong, little, left or right shoulder, etc.

Today, the guide informed us there was only very little incoming current. I was already suspicious before jumping that we might not see any action. We finally jumped, using negative entry, and there was almost no current and the channel was empty. Not a single shark. The are was covered with dead corals and nothing else to see. We searched around and end the dive after only half an hour.

We were quite disappointed because it was our last dive during holiday. I totally understand that you can't promise you will see this or that but they advertised with almost certainty we would see sharks. Furthermore, I asked the guide why didn't we check tide table to predict the current? And he said they didn't use it because it had nothing to do with tide table. I was quite surprised because I thought tide table was used to predict current.

Is this a common practice in Maldives where the guide jumps first to check the current instead of using tide table? Thank you.

 

[wspalding]

Currents aren't really driven by the tide.

 

[Storker]

Currents aren't really driven by the tide.

I disagree.

Some places, the currents are driven by the tide, some places the currents are driven partially by the tide, some places currents aren't driven by the tide. It all depends on local factors. Local knowledge of the conditions and what determines them is paramount.

 

[tursiops]

@Storker is exactly right. (Ocean currents are my business.) Currents are caused by tides, winds, ocean eddies, large-scale patterns (like the Gulf Stream), and sometimes waves (especially long waves, like tsunamis), Prediction is problematic unless just one or two of these factors is present, and even then the currents are greatly modified by topography. Local knowledge is almost always better than sophisticated mathematical models. Even when the tides are the dominant cause of the currents, if the location has both daily and twice-daily tides, the interaction is messy, and somewhat unpredictable.

As to the OP's question, is it common practice to jump in and estimate currents?..Yes, is the answer. The only surprising thing is that the dive was not scrubbed and another site substituted. No current usually means no sharks in those situations.

As to the implied question, would tide tables have helped? I have no idea, it depends totally on the specific location and a lot of data/analysis to determine how important the tides are relative to the other factors. At Blue Heron Bridge, for example, tides are 98% of the currents...easy to predict. In Bonaire, the long-shore currents on the west side are usually northward...but not always. Tides seem to be irrelevant.

 

[Storker]

Even when the tides are the dominant cause of the currents, if the location has both daily and twice-daily tides, the interaction is messy, and somewhat unpredictable.

An example: Where I live, we have twice-daily tides. They're quite regular, with about 12.5 hours between highs. Still, the change of the time for high tide from one day to the next can be from less than half an hour to quite a bit more than an hour. The local conditions are such that the incoming current goes along the south side of the fjord, while the outgoing goes along the north side. So, normal conditions at our training site is stronger current on a rising tide and weaker current the other way on an ebbing tide. And even then, things vary; I had a dive just a few weeks ago where the current didn't go just along the coastline, but also went in and out of the bay where there's normally no current at all. So even if things usually are quite predictable, daily variations can be rather unexpected. So, local knowledge helps, but a sanity check on actual conditions may be necessary.

 

[wspalding]

I disagree.

Some places, the currents are driven by the tide, some places the currents are driven partially by the tide, some places currents aren't driven by the tide. It all depends on local factors. Local knowledge of the conditions and what determines them is paramount.

Ok, I agree with the point you make. While I haven't dived in the Maldives and am not knowledgeable about the local conditions, from what I can tell the currents there are not due to tidal action. It does sound like currents are unpredictable there though, and can range from none to strong, and a tide chart probably would not have been of any help for the OP's dive.

 

[scagrotto]

Currents aren't really driven by the tide.

This place, which has one of the most famous tidal rapids in the world, also disagrees, in a very forceful manner: Clearly, whether you're there to dive, surf, or see the spectacle, it's a good idea to check the tide forecast.

As noted above, there are other places where the tide has little or no effect on the current. While local dive ops may have a good deal of experience you can't expect them to be experts at predicting currents that aren't largely a function of the tides. OTOH, you should expect them to choose a site based on the conditions they find rather than the conditions they hope to find.

 

[wspalding]

Maybe it's symantics, but ocean currents aren't really driven by the tide, but that doesn't mean you can't get moving water that is a function of the tide. As I said above, it sounds like the charter was relying on ocean currents which apparently are a little unpredictable in the Maldives, and if so, knowing the time of low/ high tide would not have been helpful. It seems pretty clear that if the operator goes out at same time daily that they are not relying on tidal currents.

 

[tursiops]

Maybe it's symantics, but ocean currents aren't really driven by the tide, but that doesn't mean you can't get moving water that is a function of the tide. As I said above, it sounds like the charter was relying on ocean currents which apparently are a little unpredictable in the Maldives, and if so, knowing the time of low/ high tide would not have been helpful. It seems pretty clear that if the operator goes out at same time daily that they are not relying on tidal currents.

"Ocean Currents" is usually the non-specific way of referring to the water moving, no matter what causes it.....tides, winds, earth rotation, whatever. Apparently you are using it to mean something specific; what?

 

[wspalding]

"Ocean Currents" is usually the non-specific way of referring to the water moving, no matter what causes it.....tides, winds, earth rotation, whatever. Apparently you are using it to mean something specific; what?

yes, I'm referring to continuous directional movement of water, like the Gulf Stream. And I agree that tides can meet this definition, especially near shore and my original post was incorrect. However, what I was reacting to was the discription of the OP that the dive operator scheduled the dive of interest at the same time daily. The current in this case, clearly isn't based on the tide but other causes.