Trip Report Raja Ampat, Live Report, Nov. 7-Dec. 7, 2023

[JonnieB]

Emptying the BCD when you are in a downcurrent, as you have reported on one diver doing, does not appear to me to be a correct course of action, although dropping weights would be.

But doesn't this subject the diver to an uncontrolled ascent if/when they escape the down current? It seem you're damned if you do and damned if you don't. It seems your advice to have enough lift (for DCs) and proper weighting for up currents is key.

 

[JonnieB]

All the divers reported that they inflated their BCD.

I think maybe an issue is many divers dive overweighted...either because of poor buoyancy skills or being grossly overweight. When I'm in rashies, I'm neutral with an aluminum plate and slightly negative with my SS. Thus I don't carry any lead and feel would have no problem inflating up in a DC or finning down in an UC.

 

[CWK]

But doesn't this subject the diver to an uncontrolled ascent if/when they escape the down current? It seem you're damned if you do and damned if you don't. It seems your advice to have enough lift (for DCs) and proper weighting for up currents is key.

Not in my experience. If your BCD has sufficient lift, inflate until you are neutrally bouyant. If your BCD doesn’t have sufficient lift, you will still be going down.

With a BCD inflated, you can get into an uncontrolled ascent when you break free of the downcurrent or if the downcurrent dissapates. So be prepared to dump air from your BCD if this happens.

 

[JonnieB]

Not in my experience. If your BCD has sufficient lift, inflate until you are neutrally bouyant. If your BCD doesn’t have sufficient lift, you will still be going down.

With a BCD inflated, you can get into an uncontrolled ascent when you break free of the downcurrent or if the downcurrent dissapates. So be prepared to dump air from your BCD if this happens.

I had in mind a diver in a wetsuit who has dumped their weights, even with an empty BCD, are they not at risk of an uncontrolled ascent?

 

[Dan]

As I mentioned in post #72 in this thread, Raja Ampat diver death, there won't be any current at the wall and you don't know how far (parameter d in Figure 4.7.1, below) and wide (lateral direction) the downcurrent is. My quick reaction is to swim to the wall as the current velocity would be lesser towards the wall and zero at the wall, as shown in Figure 4.7.1, below. You don't need to mess with your buoyancy, just find a way to hide/attach yourself to the wall.

I won't wander too far into the blue in places like this. So, swimming to the reef/wall would be quick, should be < 90-137 feet / minute descent.

Courtesy of John Southard, Massachusetts Institute of Technology, 4.7: Velocity Profiles

 

[CWK]

I think maybe an issue is many divers dive overweighted...either because of poor buoyancy skills or being grossly overweight. When I'm in rashies, I'm neutral with an aluminum plate and slightly negative with my SS. Thus I don't carry any lead and feel would have no problem inflating up in a DC or finning down in an UC.

I intentionally dive about 1kg overweight.

I had in a diver in a wetsuit who has dumped their weights, even with an empty BCD, are they not at risk of an uncontrolled ascent?

Yes. You are correct. If you dump weights, you put yourself at risk of an uncontrolled ascent.

I don’t dive with weights that can be dumped so I don’t think of this angle. All my weight is on my backplate and wing, which I have no intention of dumping, unless something extreme and as yet inconceivable to me persuades me to do so.

 

[JonnieB]

As I mentioned in post #72 in this thread, Raja Ampat diver death, there won't be any current at the wall and you don't know how far (parameter d in Figure 4.7.1, below) and wide (lateral direction) the downcurrent is. My quick reaction is to swim to the wall as the current velocity would be lesser towards the wall and zero at the wall, as shown in Figure 4.7.1, below. You don't need to mess with your buoyancy, just find a way to hide/attach yourself to the wall.

I won't wander too far into the blue in places like this. So, swimming to the reef/wall would be quick, should be < 90-137 feet / minute descent.


View attachment 815736
Courtesy of John Southard, Massachusetts Institute of Technology, 4.7: Velocity Profiles

This is some real technical diving...anything from MIT is definitely beyond me

 

[outofofficebrb]

As I mentioned in post #72 in this thread, Raja Ampat diver death, there won't be any current at the wall and you don't know how far (parameter d in Figure 4.7.1, below) and wide (lateral direction) the downcurrent is. My quick reaction is to swim to the wall as the current velocity would be lesser towards the wall and zero at the wall, as shown in Figure 4.7.1, below. You don't need to mess with your buoyancy, just find a way to hide/attach yourself to the wall.

I won't wander too far into the blue in places like this. So, swimming to the reef/wall would be quick, should be < 90-137 feet / minute descent.


View attachment 815736
Courtesy of John Southard, Massachusetts Institute of Technology, 4.7: Velocity Profiles

I have been on a wall in Indonesia with very strong downcurrents before. As mentioned before, there are no hard and fast rules for nature. When she's feeling feisty, she does what she wants. Firm instructions were given to not go away from the wall if it ever does occur because the downcurrents can persist away from it and if you did move away from it, you would have nothing to hold onto or climb up on and can get yourself in trouble really quickly. For that reason, and in Indonesia, having a wall is a good thing and I agree about moving towards it. In some parts of the world, it is suggested to move away from the wall because the downcurrents in other places are often more pronounced at the wall. In any case, always pay attention to briefings.

I have a video of us on the wall and you you can see all the bubbles going straight down and people hanging on the wall, trying to kick up and going nowhere..

The takeaway is that broad generalizations don't apply when it comes to nature. It really does vary.

 

[chillyinCanada]

I have been on a wall in Indonesia with very strong downcurrents before. As mentioned before, there are no hard and fast rules for nature. When she's feeling feisty, she does what she wants. Firm instructions were given to not go away from the wall if it ever does occur because the downcurrents can persist away from it and if you did move away from it, you would have nothing to hold onto or climb up on and can get yourself in trouble really quickly. For that reason, and in Indonesia, having a wall is a good thing and I agree about moving towards it. In some parts of the world, it is suggested to move away from the wall because the downcurrents in other places are often more pronounced at the wall. In any case, always pay attention to briefings.

I have a video of us on the wall and you you can see all the bubbles going straight down and people hanging on the wall, trying to kick up and going nowhere..

The takeaway is that broad generalizations don't apply when it comes to nature. It really does vary.

And what did you folks do, after clinging to the wall? How did you folk get out of it?

 

[Dan]

I have been on a wall in Indonesia with very strong downcurrents before. As mentioned before, there are no hard and fast rules for nature. When she's feeling feisty, she does what she wants. Firm instructions were given to not go away from the wall if it ever does occur because the downcurrents can persist away from it and if you did move away from it, you would have nothing to hold onto or climb up on and can get yourself in trouble really quickly. For that reason, and in Indonesia, having a wall is a good thing and I agree about moving towards it. In some parts of the world, it is suggested to move away from the wall because the downcurrents in other places are often more pronounced at the wall. In any case, always pay attention to briefings.

I have a video of us on the wall and you you can see all the bubbles going straight down and people hanging on the wall, trying to kick up and going nowhere..

The takeaway is that broad generalizations don't apply when it comes to nature. It really does vary.

I'm referring to underwater "water fall" coming from above and push you down fast. The wall is not moving, so no current there. the rough surface of the wall with coral growth, overhangs and crevices create a drag to slow down the downcurrent. There is no drag to slow down the downcurrent in the blue. That's why the parabolic profile is shown in Figure 4.7.1.

I have been on a current that is coming from the blue, pushing me up towards a wall ledge like in Blue Corner in Palau or Vilingili Kandu in Maldives or The Channel (Bigfish Country) in Maratua. Swimming laterally and away from the wall may be better in this case. I don't thing that's what's happening in Weka's Wow, Raja Ampat.

In such upcurrent into wall ledge, we actually want to drift towards the wall and get your reefhook ready to hook yourself at the wall ledge an enjoy the shark parade in the blue, as shown below.