That final 15 feet....

[guyharrisonphoto]

You can do a weight check. At the end of any shore or boat dive, when the tank is near empty, you can adjust your weighting so that your eyes are above water while still (no kicking) with a full breath, and you sink slowly when you exhale. This assures you have no buoyancy issues at the end of the dive but are not overweighted. Can also do it in a pool and make adjustments for salt water if needed, a simple formula. If your basic gear and exposure protection stay the same, you only have to do this check once because so long as you know the buoyancy characteristics of your cylinder when empty, you can then adjust for any other cylinder based on its buoyancy when empty. i.e. proper weighting with a near-empty HP steel 100 means you need 4- 5 pounds more with a near-empty AL 80. You would only have to re-do it if you have major changes in body weight, or you change your gear in a significant way such as getting new/different exposure protection).

 

[rivers]

Excellent advice I'm sure.

But hard to do if you are underweighted at the end of the dive. You lose what, about 4 pounds of gas from your tank, si?
So if you had to work hard to get submerged off the boat, you are probably going to be underweighted at the end.

Lots of folks complain about "overweighted divers", but if you're not 4 pounds overweighted at the surface, you are too light and will have a hard time going slowly enough from the 15' stop.

Which is why you weight yourself to be neutral with empty cylinders.

 

[Steve_C]

I bleed the tank down to 500 psi when doing that final weight check. Also make sure that your BCD is empty when you do it. Otherwise you will overweight.

 

[Jim Lapenta]

Proper weighting means you have accounted for the loss of ballast due to breathing the tank down.

As for that last 15 feet, I've taken as long as 15 minutes to come up from it. During that time I had fish visit me, saw turtles, eels, and idiots rushing to get to the surface only to have to bob along on the trail line while they waited their turn to get on the boat.

After having a bad reverse block years ago I am in no hurry to get out of the water in that last 10-15 feet. Especially on recreational dives.

 

[divad]

Better safe,than sorry. I shall try to slow it down.

FKafka, you make me smile.

 

[DiveNav]

.....Should it really take 15 seconds to get back to the surface from 15 ft.?

Yes - more.

Why do you want to ascend anyway and return to this chaotic surface world?

Just kidding

Alberto (aka eDiver)

 

[dumpsterDiver]

Excellent advice I'm sure.

But hard to do if you are underweighted at the end of the dive. You lose what, about 4 pounds of gas from your tank, si?
So if you had to work hard to get submerged off the boat, you are probably going to be underweighted at the end.

Lots of folks complain about "overweighted divers", but if you're not 4 pounds overweighted at the surface, you are too light and will have a hard time going slowly enough from the 15' stop.

Well then you are not over weighted are you?

 

[TMHeimer]

When doing a proper weight check you add 5 pounds or so to make sure you can stay put at the safety stop. Then still be very careful with the amount of air in the BC--If too much, it will expand a lot in the last 15 feet and maybe cause that rocketing up (think I did that once myself many years ago). Actually, no diver can ever be perfectly weighted as the tank is always getting lighter during the dive (unless you want to pick some exact specific time down to the millisecond at one point). Another interesting point I read about somewhere is that safety stops apparently used to be at 10 feet. Not sure how that depth was arrived at, but at some point it was changed to 15' to avoid possible wave/surge action and boats on the surface. If 10' was really the optimum depth, I would think they maybe shouldn't have changed that. Then there is the discussion about whether to do deep stops first--apparently not really enough data to recommend doing that or not.

 

[WarrenZ]

As most have said the last 15 feet is the biggest /fastest pressure change however one thing I try to stress to new divers I am diving with is most small boats draw less than 15' of water and doing a slow spiral ascent allows you to lok around and make sure the rib or another boat hasnt drifted above you. The last thing you want to do is knock yourself out on the bottom of your boat and or its ladder because you didnt see it.

 

[tlj3071]

That exact scenario happened on my last dive in St. Thomas - while I tried to stretch the time from 15', everyone else left quickly for the surface after the safety stop. One diver actually hit his head on the bottom of the boat as he was [apparently] not paying attention. When I finally surfaced, I had no wait on the line - the last diver was just getting aboard as I swam up to the ladder.