diving thirds vs rock bottom

[GrumpyOldGuy]

Why would you say that? The captain most certainly SHOULD be prepared to leave the line to recover a diver if necessary. Why must he stay?

You pulled his quote out of context, it was "the captain cannot leave the ascent line to chase you until all the other divers are up". The point I got from his post was all divers should be prepared to ascend away from the boat with a SMB deployed, to warn boat traffic and give the boat crew an early indication of where you are (before you drift farther away).

Leaving a line / anchor is not a big deal, starting up the engines when you might have divers under the boat is. Remember the context is the dive plan is return to the boat, so that is were they are like to be. The offending party may just need a little time to float and think about why and how they ended up in this predicament anyway.

 

[boulderjohn]

Why would you say that? The captain most certainly SHOULD be prepared to leave the line to recover a diver if necessary. Why must he stay?

I would say that because I have heard two different captains say that, and because there was a thread on ScubaBoard about two years ago about just such an incident. Yes, he can go at some point, but it is a problem when he is moored to the line and there are divers coming up the line and getting on the boat.

A few months ago my buddy and I surfaced from a South Florida drift dive, dive float and all, to find big waves and no boat in sight. We were on the surface waiting for close to 20 minutes before we saw the boat coming toward us. The explanation was that the other groups had surfaced a couple minutes before us, and by the time they had picked them up, we had drifted out of sight in the strong surface current. The had a pretty good idea where we had gone and were able to find us, despite the big waves that hid us. The situation is not the same, but it is analogous.

 

[lowviz]

...//... The offending party may just need a little time to float and think about why and how they ended up in this predicament anyway.

A lot of good recreational diving is in the shipping lanes, could give them very big things to think about...

View attachment 134414

 

[GrumpyOldGuy]

A lot of good recreational diving is in the shipping lanes, could give them very big things to think about...

View attachment 134414

It sure could.


I am not a captain (just have a little boat) so my answers are totally questionable....
1) If there is a dive site up current and next to a shipping lane, a chase boat is probably in order and could be set up ahead of time for fast reaction.
2) For real shipping (not pleasure craft), a quick radio call on the distress channel is the fastest way to alert large craft (that are supposed to monitor this channels)
3) Site like this are probably not a good choice for the inexperienced diver.
4) All divers should learn to deploy their SMB underwater. It's no shield, but its the one thing every diver can do himself without relying on the captain, DM or others.

 

[Rainer]

RB for deco dives is pretty straight forward. Think of RB as a limit. Your other limit for the dive is time. When either time or rock bottom is reached, the thumb comes out and everyone heads home. If you have to leave the bottom early, you will either have an excess of gas (this is good) or be at your rock bottom value, but before the end of your planned bottom time. This is ok, too, since everyone has enough gas to get their buddy to the first gas switch.

Hitting RB/min gas does not always mean thumbing the dive. It just means getting shallower. For *many* of our open water dive sites, you can easily come up a bit and continue your dive staying above the new RB/min gas limit. My favorite OW dive sites all basically allow for such multi-level profiles. For recreational profiles, this just means committing a few (e.g. 100', 80', 60', shallower) volumes of reserve gas to memory and having teammates signal to jump shallower if any hit a limit.

---------- Post Merged at 01:45 PM ---------- Previous Post was at 01:40 PM ----------

If I am correct, the policy with that boat on recreational dives is that ascending on the anchor line is always strongly recommended but never mandatory.
​

Most of my boat diving (the vast majority) has been in areas (Northeast and Southern California) where ascending the anchor line is the norm. At least in the NE (MA), it was highly stressed that coming up the anchor line should be attempted even for "recreational divers". From my earliest boat dives in the region, we always used reels and planned thirds (after reserving min gas). With strong currents, very cold water (down in the 30sF in winter), floating gill nets (probably the strongest reason to come up the anchor line, IMO), and dive sites often near/in shipping lanes, the diving was just not amendable to free ascents.

 

[lowviz]

...//...
1) If there is a dive site up current and next to a shipping lane, a chase boat is probably in order and could be set up ahead of time for fast reaction. ...//...

Never done.

...//...
2) For real shipping (not pleasure craft), a quick radio call on the distress channel is the fastest way to alert large craft (that are supposed to monitor this channels) ...//...

They look and react like icebergs, I don't have too much faith that they can see a diver adrift. But there is always hope...

...//...
3) Site like this are probably not a good choice for the inexperienced diver. ...//...

Lots and lots of OW's were (and will be) generated somewhere on the pic in question...

...//...
4) All divers should learn to deploy their SMB underwater. It's no shield, but its the one thing every diver can do himself without relying on the captain, DM or others.

Yes, indeed. You tie-off to the structure and surface off the dive boat's anchor line. See "Jersey Upline". Had to do this myself, once. Such behavior is acceptable, given a good reason.

 

[GrumpyOldGuy]

Yes, indeed. You tie-off to the structure and surface off the dive boat's anchor line. See "Jersey Upline". Had to do this myself, once. Such behavior is acceptable, given a good reason.

If you can tie off the the structure and/or the anchor line, then you certainly don't need the captain to leave the line and come chasing after you.
Most captains are smart enough to select site that might be near a shipping lane, but not directly up current, there is a difference.

I think we got off on another rabbit trail...

 

[dumpsterDiver]

I would say that because I have heard two different captains say that, and because there was a thread on ScubaBoard about two years ago about just such an incident. Yes, he can go at some point, but it is a problem when he is moored to the line and there are divers coming up the line and getting on the boat.

A few months ago my buddy and I surfaced from a South Florida drift dive, dive float and all, to find big waves and no boat in sight. We were on the surface waiting for close to 20 minutes before we saw the boat coming toward us. The explanation was that the other groups had surfaced a couple minutes before us, and by the time they had picked them up, we had drifted out of sight in the strong surface current. The had a pretty good idea where we had gone and were able to find us, despite the big waves that hid us. The situation is not the same, but it is analogous.

Not sure what a drift dive with floats has to do with an anchor dive and being lost? You say that the captain can NOT come pick up divers until everyone is on the boat, because you heard people say that two times... Well that is a good reason to say it then, i guess.

I think that a responsible captain should be prepared to leave the anchor line/mooring and chase a diver that is in an emergency situation. I think most captains would not like to move the boat, but i think they normally can so it if they choose... assuming that they are tied into a mooring or have prepared for such an event by having a large float to tie off to the anchor line when leaving it.

 

[smokey braden]

all,
i want to thank everyone for contributing to this thread.
some very good information was shared by different divers who all dive looking thru different windows.
it seems that there is more than one way to skin the ole cat.
it seems most divers want to have fun but safety is the one thing we all agree. (somewhat)
thanks for y'alls thoughts.

 

[eelnoraa]

I think RB and 3rd are quite two different things, not necessary mutually exclusive. RB means the min gas to bring two divers (you and you buddy) up to surface safely while completing all necessary stops. So when your hit RB for the depth you are at, you really should start ascent. RB gas is no tank capacity dependend, but depth dependent.

Diving 3rd, the 3rd really mean 1/3*(total capacity - RB). It is capacity dependent now. It is for if you have to return to the starting point of your dive before you can ascent, ie cave diving Because you use 1/3 to dive forward, 2/3 for you AND your buddy to return, then you still have RB to ascent safely.

For most OW dive, I don't think return to starting point is absolute necessary. Say if you diving on boat at tropic, no current, calm sea. You really can use all the air you have until RB. Once hit RB, you ascent