Missing Diver - Grand Cayman Sept 21, 2009

[SCUBA482]

Thanks for the info on Walldives and currents... proof that the speculating in this thread leads to valuable information being shared!

I couldn't agree more! Glad I asked a question I wouldn't have thought of because of this incident and thread.

It depends on the down current; some can only be overcome by buoyancy. I love to dive walls and have been in a strong down current several times. I use a large wing so I've never had much of a problem, but the first time it happens to you it's an eye opener.

There's no hard and fast rule when it comes to down currents. The best defense is a good offense; be prepared! I watch the wall to watch for any shifts in the current. Generally fish will face into the current when its running. In a down current however, even large fish will be taken for a ride...

There's different schools of thought on overcoming down currents. Some say low volume BCs are better because they provide less surface area to be affected. Another group (which I agree with) is to provide greater lift to counteract the downward force and be ready to dump the buoyancy when necessary.

Some believe that it's best to hug the wall. I've noticed that if I'm away from the wall the current forces often dissipate, but you have to judge each situation as it presents itself. Being away from the wall can cause you disorientation in deep water. If you're experienced; it's not a problem, but if not, perhaps you should hug the wall.

One advantage of hugging the wall is that you can climb up or to the side. Obviously you don't want to do damage to the reef, but you may not have another option.

Generally the current will vary somewhat in velocity. When it's weaker move, when it's strong hold on.

Nitrox can also be a problem, so I never use it on walls (I often dive deep, so it's really not a gas I use often anyway).

If all else fails, remember your weight belt. Obviously drop your belt as a last resort, but keep this as an option. Personally I'd much rather deal with DCS afterwards than not make it to the surface.

Cold up currents can also be a problem, but that's another story... Dive safe!

DCBC...this is some really good information and thanks for explaining it so well...with some more speculation and theories on how to handle it I might add...I also appreciate you understanding there are different ways different skill level divers will or should handle the issue...

What was the tide doing? On an outgoing tide you can have incredible current flowing down the wall, on an incoming tide the current will be coming up over the wall. Inexperienced divers can be caught by surprise, also depth can be really misleading on a wall, 200' looks the same as 90' in clear water. Whenever I'm diving a wall, I'm constantly checking my depth and sometimes I'm still caught by surprise, the vertical surface is extremely misleading. I'm surprised that there aren't more accidents with inexperienced divers on these extremely advanced dives.

Safe Diving
Cheryl

DamselDiver...this make a lot of sense...have you found this pretty accurate in variouis locations or only in the warm island waters?

 

[Cave Diver]

It depends on the down current; some can only be overcome by buoyancy. I love to dive walls and have been in a strong down current several times.

What was the tide doing? On an outgoing tide you can have incredible current flowing down the wall, on an incoming tide the current will be coming up over the wall.

Have y'all experienced this in Cayman? If so, where?

I know this is a fairly common occurrence in Mexico, but in all my wall dives in Cayman, I've yet to experience any significant down wellings. I have seen enough current to cause soft corals to sway on the wall but not enough to cause any significantly adverse effects on buoyancy.

 

[DCBC]

DCBC...this is some really good information and thanks for explaining it so well...with some more speculation and theories on how to handle it I might add...I also appreciate you understanding there are different ways different skill level divers will or should handle the issue...

You're most welcome; glad the information helped. I might add that this phenomenon occurs as a result of strong bottom currents. The angle in which these currents interact with the wall seems to influence this occurrence more than simply an ebbing or flooding tide by itself (although it's an added complexity). This is why some walls are not routinely plagued with down currents and affect different walls at different times.

Currents are influenced by water density and temperature changes. As cold water has a higher density (due to increased saline levels) when a deep ocean current (colder water) meets warmer water, the cold water upwells or downwells. This can be changed by weather, gravitational pull of planetary bodies, tidal flow and other factors. It seems to be hard to predict (at least for me who's not an oceanographer).

 

[DCBC]

Have y'all experienced this in Cayman? If so, where?

I have only observed this once in Cayman, but it's common in Costa Rica, Tobago and the Barracuda wall (and others) in Cozumel.

As you're a cave diver, the down currents (tidal) can be killers in the Blue Holes of Andros.

 

[Cave Diver]

I have only observed this once in Cayman, but it's common in Costa Rica, Tobago and the Barracuda wall (and others) in Cozumel.

As you're a cave diver, the down currents (tidal) can be killers in the Blue Holes of Andros.

Yes, I'm aware of the common down welling in other locales. Since I've never encountered it in Cayman, I was curious of the relevancy as it relates to this particular accident.

 

[DamselDiver]

I only dive in warm waters. The important thing to remember is that the ocean isn't a static body of water. Everyone needs to have situational awareness and realize that conditions can change dramatically in a short period of time. Weather can move in suddenly, the tide can change during a dive and vis can go to hell, or a current can pick up or reverse suddenly.

The important thing is to have a plan in place when the unexpected happens. It's nice to have a buddy, but every dive is a solo dive.

Safe Diving
Cheryl

 

[DCBC]

Yes, I'm aware of the common down welling in other locales. Since I've never encountered it in Cayman, I was curious of the relevancy as it relates to this particular accident.

Like I said, I've experienced this on the Cayman wall. As to the other locations, I was simply trying to answer your question.

As your aware, Cayman has two wall systems. The second or deep wall drops over one mile. The south part of the trench is over 20 K ft deep; so given the complexities of such a wall (and the deep currents that exist), down currents are something that should be considered in the dive plan.

 

[Cave Diver]

Like I said, I've experienced this on the Cayman wall. As to the other locations, I was simply trying to answer your question.

Have y'all experienced this in Cayman? If so, where?

My question of "If so, where?" was meant as an inquiry as to what part of the island you had experienced such a down welling. Sorry if that wasn't clear.

I have only observed this once in Cayman

It would be interesting if you shared the details of this experience as it may have bearing on this particular discussion.

 

[Drew Sailbum]

What was the tide doing? Safe Diving
Cheryl

The accident occurred in the morning during a wall dive. Normally that would be the first dive of a two tank trip.

According to the tide calculations from www.bsac.ky which pulls data from www.irbs.com , the tide should have been rising at that time and quickly approaching high tide. That would presumably preclude downwelling.

High tide occurred at 11:20am with a low approximately 3 inches lower following at 4:03pm. Tide rose again until the next high at 8:12pm. Tide fell again until a low at 4:13am the next day.

Total tidal variation that day from highest high to lowest low was about 18 inches. This is about the maximal tidal variation for the year as expected for a date so near the equinox.

Have y'all experienced this in Cayman? If so, where?

I have experienced a substantial downwelling one time along the North Wall on a dive at Tarpon Alley. This is the only noticable downwelling I have experienced in Cayman in 3000+ dives. Downwellings are rare here.

 

[DCBC]

My question of "If so, where?" was meant as an inquiry as to what part of the island you had experienced such a down welling. Sorry if that wasn't clear.

The Bloody Bay Wall often has strong currents in the summer; which at times can be even experienced on the surface. They can be extremely strong at depths over 150 ft pulling the diver off of or downward or into the wall or upward.

Most of Cayman's walls have little or no current at the depths normally dove by the masses during the winter months. If you want something more extreme just talk to the guys at Divetech (or other locals in the Tech community).