Dive Profile Feedback

[mrlipis]

Here is a dive profile lead by an instructor in Roatan last week. I routinely listen to dive briefings and neither me or my wife heard anything about a depth of 105 ft. We both had fills under 2800. I just downloaded my dive computer so I know this data is accurate.
Drop down on reef and spend 19 minutes at 40 to 45 ft. I am taking pictures as we start down a sandy shoot. The yellow jawfish are out of their holes and dancing on the sand. I am taking pictures as we move down this shoot. As we come out on the wall we are at 105 ft 23 minutes into the dive. We swim along the wall and ascend to 45 ft and reach that depth at 27 minutes into the dive.

I am aware of my responsibility, so I am not really looking for any tongue lashings here.
I have no problem diving to 100+ depths but it something I prefer to know in advance, especially with a 2750 fill.

I am curious of some opinions of this type of profile. I may be wrong but this just seems like a terrible dive profile and poorly executed dive by the instructor.

Bruce

 

[TSandM]

How long was the total dive? You spent 19 minutes shallow, then 8 minutes deep -- if you then spent anothe 20 minutes shallow, I see no problems with the dive from a profile standpoint.

Diving to 100 feet on an Al80 means that a lot of your tank is safety reserve ("rock bottom"), but one would hope you still had 1600 psi at minute 27, and if you did, the gas worked out OK. If you didn't, then you might not have had enough gas to get two of you up from the bottom if something blew out at the deepest part of the dive.

If the dive brief didn't give a maximum depth, then I would have expected someone to ask that, since it's a key part of dive planning. If the max depth was briefed at 45 feet and you ended up at 105, both the dive leader and you and your buddy made a mistake. The leader, by taking you so far below the agreed depth limit, and you, by not noticing you were going there.

 

[mrlipis]

I had exactly 1600 psi at the 105 depth and the total dive was 52 minutes. Thanks for the feedback, I respect your opinions, I just felt it was late in the dive to drop to that depth. To be honest I don't remember what our maximum was suppose to be but most of the dives are in the 60 to 70 ft range.

Bruce

 

[NorthWoodsDiver]

The problem I see besides gas supply is narcosis, in my experience the narcosis has always been worse if I spend time shallow then go deeper. though 105' is pretty shallow so I wouldn't see the narcosis as being to bad for most people at that depth.

 

[knotical]

Interesting question, mrlipis. Can we broaden the focus?

We’re usually taught in basic diving classes to do the deepest part of our dive first, as you address in your opening post.

We’re also taught to avoid saw tooth profiles. But what defines saw tooth? Is a foot or two up and down OK? 5 feet? 10 feet ? etc. Where is that defined?

And we’re taught to do our deepest dive of the day first, although there are now some studies that indicate it is not the prohibition once thought.

What are the real issues associated with such rules of thumb? Do models “penalize” us for such practices, or are they even addressed?

 

[LeadTurn_SD]

Interesting question, mrlipis. Can we broaden the focus?

WeÃÓe usually taught in basic diving classes to do the deepest part of our dive first, as you address in your opening post.

WeÃÓe also taught to avoid saw tooth profiles. But what defines saw tooth? Is a foot or two up and down OK? 5 feet? 10 feet ? etc. Where is that defined?

And weÃÓe taught to do our deepest dive of the day first, although there are now some studies that indicate it is not the prohibition once thought.

What are the real issues associated with such rules of thumb? Do models ÅÑenalize us for such practices, or are they even addressed?

Interesting questions.

I don't see any problem with the actual dive profile, just the apparent lack of a proper briefing and plan, and potentially not enough reserve gas for an emergency at the max depth as TSandM stated above.

The way I view the profile overall is as a very gradual descent, 4 minutes at depth, followed by an ascent. I agree it may be more common / better(?) that the descent to 105' would have been made right at the start of the dive (if only for gas-reserve reasons) rather than midway through the dive, but I see no "sawtooth" in the profile if I'm reading the post correctly.... but yes, it would be interesting to really know how risky a true sawtooth profile would be in this case (for example, if the DM had led them back down to 70 feet to show them something after they had ascended to 45 feet....).

Best wishes.

 

[TSandM]

I know a lot of boat dives use the profile where you go to your deepest point at the beginning of the dive (which makes sense from a gas reserve standpoint) and then work your way up as the dive progresses. But I do a lot of shore diving, where we start from relatively shallow, work our way deep, and then work our way back up -- not too different from the profile you describe. I don't believe anybody has ever shown that there are DCS problems with this type of dive. The "reverse profile" issue is doing the first dive shallow and the second dive deep, and even then, there isn't much to support this being an increased risk activity.

Minimal gas reserves, and confusion as to the max proposed depth, are the issues I see here.

 

[mrlipis]

I have experienced my share of saw tooth profiles myself, as a result of following a divemaster. I think we/I have a tendency to trust DMs, but ultimately we are responsible for our own profiles. On the other hand, is it prudent to bailout on a dive group. We did another deep wreck dive to 113 ft. 10 or 12 minutes into the dive my dive computer was barking at me, "high nitrogen", and me and my buddy ascended above the rest of the group and waited for them at about 80 ft. For me that was a no brainer. I appreciate the feedback as this sport is a continuous learning experience.

Knotical.... long time no talk.

Bruce

 

[ScubaSteve]

.....On the other hand, is it prudent to bailout on a dive group......

IMO yes it is as long as you and your buddy go together and safely. To leave a group for no good reason would not be prudent however if you exceed your NDL limits or training/comfort, then you owe it to both yourself and your buddy to safely bail on the group. As you mentioned, you can often times ascend but keep them or their bubbles in sight. That way you do not lose them. But to stay down just because, even though "something is not right" is almost always the wrong answer.

 

[knotical]

Knotical.... long time no talk.

Hi Bruce.

Yeah, it has been a while. I'm glad to see you're still actively diving, - and still questioning.

Back when we could type our own title above our avatar, I called myself "perpetual scuba student", and it still applies. After almost 50 years intermittently hanging around this stuff, I'm repeatedly reminded how little I know. And how so much conventional wisdom later turns out to be conventional, but not necessarily wisdom.

I continue to enjoy your questioning mind. Happy bubbles.

k