The Last 10 Feet

[mccabejc]

Started going thru the graphs of my dives, and began to look at whether I have been handling the last 10-15 ft. of my ascents correctly. I think there was, at least with me in the beginning of my diving, a subconcious sense that "hey, being at 5 or 10 feet deep is no different from being in a swimming pool, so you don't have to be as rigorous in monitoring your ascent". I quickly learned that's wrong, but anyway...

So while looking at my graphs I remembered that my computer (Cobra) goes into Surface mode when you rise above 4ft. Which means that you don't get any more samples at less than 4ft. And that raises some kind of conundrum or something:

Assuming a 10 second sample rate, if the last sample shows you at, say, 10ft, then that doesn't necessarily mean that your final ascent was at or faster than 10ft/10 seconds (or 60 ft/min). It could have been as slow as 6ft/10 seconds (or 36 ft/min).

Bottom line: Your final ascent rate may not be as bad as you thought. On the other hand, it may be much worse. :11:

I guess it comes down to taking the last 10-15 feet very slowly.

 

[JeffG]

Started going thru the graphs of my dives, and began to look at whether I have been handling the last 10-15 ft. of my ascents correctly. I think there was, at least with me in the beginning of my diving, a subconcious sense that "hey, being at 5 or 10 feet deep is no different from being in a swimming pool, so you don't have to be as rigorous in monitoring your ascent". I quickly learned that's wrong, but anyway...

So while looking at my graphs I remembered that my computer (Cobra) goes into Surface mode when you rise above 4ft. Which means that you don't get any more samples at less than 4ft. And that raises some kind of conundrum or something:

Assuming a 10 second sample rate, if the last sample shows you at, say, 10ft, then that doesn't necessarily mean that your final ascent was at or faster than 10ft/10 seconds (or 60 ft/min). It could have been as slow as 6ft/10 seconds (or 36 ft/min).

Bottom line: Your final ascent rate may not be as bad as you thought. On the other hand, it may be much worse. :11:

I guess it comes down to taking the last 10-15 feet very slowly.

By the time you download the profile its too late. And since you can still download it to your PC..your still alive...

So....Don't sweat the small stuff and don't worry overmuch about what the computer shows.

Ask yourself...did you or did you not do a good job on that dive (How do you feel???...was there anytime you were out of control???????)

 

[DandyDon]

10 second sampling? I think I changed mine to 2 second. Can you change your's?

My Pelagics go to SI around 4 feet, too, or close. :colgate:

 

[JeffG]

10 second sampling? I think I changed mine to 2 second. Can you change your's?

And what good does that do? What real useful info do you get from that?

 

[MXGratefulDiver]

Started going thru the graphs of my dives, and began to look at whether I have been handling the last 10-15 ft. of my ascents correctly. I think there was, at least with me in the beginning of my diving, a subconcious sense that "hey, being at 5 or 10 feet deep is no different from being in a swimming pool, so you don't have to be as rigorous in monitoring your ascent". I quickly learned that's wrong, but anyway...

So while looking at my graphs I remembered that my computer (Cobra) goes into Surface mode when you rise above 4ft. Which means that you don't get any more samples at less than 4ft. And that raises some kind of conundrum or something:

Assuming a 10 second sample rate, if the last sample shows you at, say, 10ft, then that doesn't necessarily mean that your final ascent was at or faster than 10ft/10 seconds (or 60 ft/min). It could have been as slow as 6ft/10 seconds (or 36 ft/min).

Bottom line: Your final ascent rate may not be as bad as you thought. On the other hand, it may be much worse. :11:

I guess it comes down to taking the last 10-15 feet very slowly.

That last 10 feet should take you 20 seconds, minimum ... if you're doing it properly it will feel like you're hardly moving at all.

... Bob (Grateful Diver)

 

[jbisjim]

I leave mine at a 10 sec sample rate. It hold more dives for me.

If you go back to Boyles law the greatest changes is in the first 33 feet. So the last 10-15 should be handled very slowly.

That last 10 feet should take you 20 seconds, minimum ... if you're doing it properly it will feel like you're hardly moving at all.
... Bob (Grateful Diver)

Well said.

Think of it like the commercial for the Navy where the Seal comes up with his mask half out of the water. Except you wont have a machine gun in your hand.

 

[OE2X]

Just to add onto this is a point that OneBrightGator made on another post about weighting.

Most people do their weight check to achieve neutral bouyancy at 15' on a tank with 500 psi or less. What OneBrightGator pointed out was that this was incorrect. You need to be neutral at the surface. With full lungs you should be positive, empty lungs slightly negative.

If you don't do this, then you won't be able to control your ascent rate during these last 15'. Keep in mind that you may also have some residual air in your drysuit (if you dive dry) that will also effect this.

 

[Henryville]

Why not consider a brief stop at 10 feet?

For me, momentum is sometimes the problem. I lose concentration or otherwise don't manage buoyancy as carefully as I should, and the wetsuit is expanding, so 10 feet to zero is a challenging zone for me. I started spending an extra 30 seconds to a minute at 10 feet, and the consciousness of needing to physically stop at that depth has helped me avoid blowing through ten and on up to the surface.

 

[MikeFerrara]

We've kind of settled on 5 ft/minute from 20 ft to the surface for most dives. On deeper dives we cut that in half.

 

[mccabejc]

Who said "don't sweat the small stuff??" If you ascend too fast you can die. That's big stuff. And yeah, I guess I'm a little obsessive-compulsive, too...

Anyway, I'm a new diver (22 dives), and I'm trying to improve my skills, including how I ascend. So I'm going back over my previous dives to see how I've been doing.

And I really don't like the Cobra's 10 second minimum sample rate for graphs. Hell, you can do a lot in 10 seconds. I want to be able to look back and see if there's EVER a point in my dive where I exceeded the max. ascent rate, and with a 10 sec sample rate you can never be sure.

For example, a while back we were diving a reef in some pretty big surge, and entered a crevice. The surge drew us in pretty quickly, and the crevice got progressively shallower, then it drew us out. It happened pretty quickly, so for all I know it could have drawn us up 5 or 10 feet in a few seconds. Well, maybe 5. But nothing on my graph shows that. Luckily nothing happened, but if I had some symptoms afterwards I wouldn't have been able to understand what happened.

When I ascend, I keep my eyes glued to the ascent rate indicator on my Cobra, and make sure I'm at only one or two bars. Wish it had a numerical ascent rate indicator instead of bar graphs.

Anyway, anyone know of a computer with a numerical ascent rate indicator AND a shorter sampling rate (2 seconds sounds nice...)? Would also be nice to have a little warning that comes up on the display and stays on which indicates you exceeded a pre-set ascent rate.

The other thing I don't like about the Cobra is that the time display is on a different screen from the Dive Display, so it's an either/or: you monitor time or you monitor the ascent bar graph.