Question onproper weighting...

[MikeFerrara]

FatCat once bubbled...


True Mike, very true but with some new divers it's next to impossible to get them down.

Once they realise that they're not getting down because they:

1. are stiff as board 'cause they're nervous
2. inhale on descent instead of exhaling
3. dive rental gear, so buoyancy varies from one dive to another
4. move too much

which is round about dive #20, they can start taking weight off.

Now I've been known to spend more than an hour getting a student to descend while explaining he/she shouldn't (see above), but not every instructor has that kind of patience or time, so extra weight is put on.

Besides, I think that explaining to OW students about keeping some air in their BC's while descending, might confuse the issue. Neptune knows that buoyancy for some reason is a difficult subject for many students.

That said, I do teach the controlled descent in the PPB specialty. Now if only I could get people to understand that this isn't a waste of money, I'd be a happy man.

Sinkingly yours,

The Cat

I certainly understand your points but I won't have a student in OW untill they can demonstrate controlled ascents and descents in confined water along with an understanding of the buoyancy priciples that apply.

Controlling our position in the water IS what diving is. If a student can't do it then we haven't taught them to dive.

When I get a student for a continuing ed class like AOW, nitrox or whatever I do a skill preassesment. I ask them to descent to 10 ft as a buddy pair, hover facing each other and the continue down when signaled and stop above the platform/bottom while facing each other again. After air sharing and mask skills midwater we ascend using the same routine as on the descent. If a diver can't perform a controlled descent, staying with their buddy all the way down and the other skills while controlling depth then we don't do the dive. These divers need to stay at 20 ft in a controlled environment until they get the basics down.

 

[MikeFerrara]

donacheson once bubbled...


While you're precisely correct, IMHO there's no practical difference between being neutral with an empty BC and near-empty tank at 15 feet or the surface. Wet/dry suit compression is the only issue.

If a line is available for a safety stop, it can be used to control one's ascent to the surface. While diving in the tropics, wet suit compression is negligle. Even with a heavy neoprene suit on, gentle swimming or controlling one's breathing can easily accomodate the increase in buoyancy associated with wet suit compression above 15 feet.

If a line is available
If inert gas lods are minimal
If one doesn't need to be at 5 or 10 feet for an extended period
If...
If...
and if

Dive weighted such that you can control position at any depth without swimming or holding on to something.

Around here wet suit compression is very significant in the top few feet because divers are wearing lots of rubber. Propper weighting works every place while improper weighting only works if you're lucky.

 

[MikeFerrara]

Don Burke once bubbled...

Coming up that last few feet two or three pounds positive isn't going to be a crisis.

It might not always be a crisis but why would you want to?

 

[Don Burke]

MikeFerrara once bubbled... It might not always be a crisis but why would you want to?

The plan is to come up. Three pounds of force on 250 pounds of diver and gear over ten feet isn't going to get him going faster than about 20fpm, less if he's horizontal.

Yes, when my tanks are empty, I do want to come to the surface.

 

[Warren_L]

I like to be slightly negative at 15 feet for precisely that reason - I don't like poping to the surface uncontrolled (or having to fight to keep it under control) as I come up from the safety stop.

 

[MikeFerrara]

Don Burke once bubbled...
The plan is to come up. Three pounds of force on 250 pounds of diver and gear over ten feet isn't going to get him going faster than about 20fpm, less if he's horizontal.

Yes, when my tanks are empty, I do want to come to the surface.

In the general case you won't be comming up with an empty or near empty tank. If there's a problem on a dive though it can happen. Maybe an equipment failure causes you to lose a significant portion of your gas. Maybe you were delayed by a problem. Maybe you suffered a total gas loss and are sharing air with a buddy. In some cases a slow ascent after a problem dive may be even more important than usual due to extended times or stress. Try staying with the buddy you're sharing air with on a nice slow ascent if you're positive.

I ascend the last 20 ft of a dive at about 6 ft/minute/After a more significant dive I ascend at 2 feet/minute. Try two feet/minute when you're too light (even a couple pounds).

There just isn't any reason for it.

 

[donacheson]

MikeFerrara once bubbled...


Around here wet suit compression is very significant in the top few feet because divers are wearing lots of rubber. Propper weighting works every place while improper weighting only works if you're lucky.

I never had any problem slowly ascending from 10 or 15 feet, where I was neutral, in a full 1/4-inch wet suit.

As I said, you're precisely correct, but in practice it isn't a big deal. However, I do agree that it's best to teach one correct way: empty BC, near-empty tank, just below the surface.

 

[Don Burke]

MikeFerrara once bubbled... I ascend the last 20 ft of a dive at about 6 ft/minute/After a more significant dive I ascend at 2 feet/minute. Try two feet/minute when you're too light (even a couple pounds).

Try that with two foot waves. If I can't do it anyway, I see no reason to weight for it.

 

[MikeFerrara]

Don Burke once bubbled...
Try that with two foot waves. If I can't do it anyway, I see no reason to weight for it.

You weight for it because if you don't you can't ever do it.

Two foot waves aren't a problem. I'm pretty happy if we get out on the Great lakes and it's that flat.