What if...? Dive Planning & Trust Me Dives

[Kenny13]

A lot of variables can affect the choice. One point of this particular exercise is to give you some thoughts about what you can do in advance (like Flots mentioned) to avoid this situation to begin with.

Without having yet even considered a dive like this, I would think that this is definitely something that would have to be part of the dive plan. It certainly wouldn't be the first time conditions have changed in the middle of the dive and you should always be prepared to expect the unexpected.

 

[MRadke]

Part of the problem with the dsmb on too short of a line is at some point you have to choose the lesser of evils. You are either going to be drug down current much faster than you would otherwise, which isn't the end of the world, or be drug into a much quicker ascent than is prudent, risking the bends. Your only other option at that point is to release the signalling device, leaving you with nothing to show your position.

 

[Cave Diver]

Without having yet even considered a dive like this, I would think that this is definitely something that would have to be part of the dive plan. It certainly wouldn't be the first time conditions have changed in the middle of the dive and you should always be prepared to expect the unexpected.

Exactly. You don't know what you don't know, so it's hard to take all the variables into consideration until you've learned a few lessons.

Yes, this is all basic physics but the SMB will eventually surface, given enough line. I was trying to determine if you believed (through experience I don't have) that the current would still keep it under. So you're assumption is that the line is short or that by the time it did surface it would be too far away?

Having divers "weighting" the line would definitely have a negative effect on it surfacing well.

The line is going to be too short. The current is going to pull the bag sideways instead of allowing it to go straight up. The angle at which it's pulled sideways is going to depend largely on how much current is present and the size of the bag. I carry 1.5 times the amount of line for my planned depth and prefer 2x whenever possible.

 

[rhwestfall]

I was reading my way through this before I posted so you answered before I got to typing... - yes, the spool was too small for the job..... My anchor line for my boat is 250' (and I have a spare 100' stored) for typical 100' depths......

Proper gear for the situation....

 

[boulderjohn]

I was reading my way through this before I posted so you answered before I got to typing... - yes, the spool was too small for the job..... My anchor line for my boat is 250' (and I have a spare 100' stored) for typical 100' depths......

In any situation like this, if one end of the line is anchored and the other is flowing in the current, there will be a significant slope to the line. If both are flowing in current, though, it will be quite different.

On the last dive I did, there was a very long line attached to the wreck in heavy current, and it was significantly sloped. As we left the wreck, we untied and the line went slack. By the time we were doing our deco stops, we were just hovering nearby and watching the line hang straight down as we all drifted along in the current.

Similarly, if shooting a bag from a wreck in current, you have two choices, depending upon how much line you have. You can start your ascent and then shoot the bag, or if you have enough line you can shoot the bag and immediately get off the wreck and start the drifting ascent. Either way, you will soon have a vertical line. During a safety stop you can watch the spool or reel dangle in front of you.

Of course, the problem with that in this scenario is that your boat is moored and cannot follow you until everyone else is on board. They will need to keep an eye on you as you drift, and if you drift too long, it could be a problem. That is why it is something to be avoided. If you ever have to do this, you should therefore shoot the bag as soon as possible so it comes up close to the boat.

Your better choice is to make good decisions about your gas management in the first place so that you can get back to the ascent line without getting into this mess.

 

[rhwestfall]

I was merely addressing the appropriate gear, not an action step (and paralleling it to how in a similar situation, an anchor rope for a boat isn't based on the actual depth). I completely agree - nothing beats planning a dive, and diving a plan.......

 

[MXGratefulDiver]

The line is going to be too short. The current is going to pull the bag sideways instead of allowing it to go straight up. The angle at which it's pulled sideways is going to depend largely on how much current is present and the size of the bag. I carry 1.5 times the amount of line for my planned depth and prefer 2x whenever possible.

... and if that bag's an open or semi-closed type system, it's gonna start getting awfully heavy once the current starts pulling it sideways and displacing some of the air in the bag with water ... (go ahead, ask me how I know this) ... :shocked2:

... Bob (Grateful Diver)

 

[Jax]

Me either, but I can tell you that current enough to make a detuned Dive Rite reg free flow is enough to pull a fullsize beer keg attached to a 5/8' line 3' under water when a couple of divers are hanging on the line.

Is this some kind of camelbak arrangement to keep people from being bored while on deco?

 

[Jax]

Alternate mooring lines are a good potential options for the SG (and it happens quite a bit), but I'd like to see other thoughts in case they aren't available.

So if one is forced up an alternate mooring (for the reasons given in the scenario), do you tie off (hopefully you have a jon line) to the mooring ball?

Or hang off and send up an SMB?

All I remember about our wreck dive briefing is that you owed every member of the crew a case of beer if you came up the wrong line . . .

 

[Cave Diver]

... and if that bag's an open or semi-closed type system, it's gonna start getting awfully heavy once the current starts pulling it sideways and displacing some of the air in the bag with water ... (go ahead, ask me how I know this) ... :shocked2:

... Bob (Grateful Diver)

How do you know?

Is this some kind of camelbak arrangement to keep people from being bored while on deco?

No, just a creative solution to a lack of a fixed mooring ball.

All I remember about our wreck dive briefing is that you owed every member of the crew a case of beer if you came up the wrong line . . .

I've heard similar similar briefings about coming up on the wrong boat/mooring, whatever. Often, it's just friendly ribbing, but I disagree with using this method. It puts more stress on inexperienced divers to try and get back to their boat, instead of looking at other possible options.