"proper" weighting vs Rock bottom

[Sideband]

Things aren't lining up correctly in my head on this. There are several schools of thought on weighting:
Neutral at 15' with 500psi
Neutral at surface with 500psi

Then we have Rock Bottom pressures. Using this you should never be at 15' or the surface with only 500psi unless you had to share air.
This seems to me like it should be easy but every time I hear someone talking about where you need to be neutral they bring up the ease or difficulty of ascending the last 15'.
I personally weight for neutral at 15' at 500psi but am generally at about 750 - 1000psi when I get there (depending on depth).

I don't know what I wanted from this other than to mention it. It could almost go into whine and cheese but it is more scuba related than most of those.

Joe

 

[nolatom]

I'd prefer to be a pound or two heavy at 15' so I don't become positive while trying to ease slowly up to surface from there.

How much air depends on lots of things--vis, temperature, current, max depth, buddy, free ascent or line, yada yada. In good conditions, I'd rather get to safety stop with about 600psi, and you use it so slow you'll still have 500 on surface next to the boat, which is usually plenty.

 

[roakey]

Then we have Rock Bottom pressures. Using this you should never be at 15' or the surface with only 500psi unless you had to share air.

So in theory using Rock Bottom you and your buddy could surface with zero pressure (if you didn't pad, yadda, yadda, I'm not going into Rock Bottom here, there's plenty of duplicate posts on the subject already). The last thing you want to be is struggling to stay down in an emergency situation, so you want to be neutral with zero pressure in your cylinder. That's kinda hard to do, so with as little pressure in your cylinder as possible (so you can breathe) adjust your weighting for neutral at the surface (or more correctly, just below the surface), since the ascent from 15/5 (or 10/3, if you're doing formal decompression) is the most critical for making a slow, controlled ascent.

Roak

 

[sbrooks]

I've been neutral/slighltly positive at 15' with no in my BC - I surfaced with about 550-600 psi... Fortunately I had an ascent line and it wasn't too big of a deal. This was the first dive that I dropped weight - 4 pounds. I learned my lesson.
S.

 

[Bobbin-along]

I'm weighted to be neutral at 15' with 500psi. Here's my logic.

1. We follow rock bottom rules for all our dives.
2. We rarely do boat dives, instead prefer ease of shore diving.
3. With most dives being shore dives we do our safety stop and then mosey around in the shallows playing in the eel grass, kelp, and rocks til we drop to 500 psi. Then swim our way to about 4' of depth. It's our time to enjoy the little critters, fine tune buoyancy, practice skills, and whatnot.


So that's what works for us.

 

[Blackwood]

The 500PSI "rule" is so arbitrary that it can be disregarded. It plays no role in actual dive planning.

you want to be neutral with zero pressure in your cylinder.

Aye.

IMO:

1) Carry at least enough stuff to maintain neutral buoyancy for the duration of the dive.
2) Carry no more much stuff than you can swim up without ditching.

I consider those to be the extremes: (1) is minimum, (2) is maximum, and anywhere in between is acceptable.

 

[ianr33]

I dont follow your logic ! If you are neutral at 15' with 500 psi then you will be positive at 4' (unless you are wearing swimtrunks only) How do you stay down? Grab hold of the bottom?

I like to be weighted to be neutral at the surface with empty tanks.Why? Just in case I ever need to do it for real.

I would much rather be 4 pounds heavy than 1 pound light,especially on deco dives.IMHO people obsess too much about dropping as much weight as possible. A couple of pounds too much is no big deal.

 

[The Kraken]

ianr33,

You make a very, very good point!

the K

 

[Blackwood]

I would much rather be 4 pounds heavy than 1 pound light,especially on deco dives.IMHO people obsess too much about dropping as much weight as possible. A couple of pounds too much is no big deal.

Yah. Weight requirement, like air consumption, has become some sort of competition with some people.

It's rather stupid.

 

[Charlie99]

I like to be weighted to be neutral at the surface with empty tanks.Why? Just in case I ever need to do it for real.

I would much rather be 4 pounds heavy than 1 pound light,especially on deco dives.IMHO people obsess too much about dropping as much weight as possible. A couple of pounds too much is no big deal.

In general I agree with your thoughts, but do remember that weighting isn't a completely black and white sort of thing. Your breathing changes your buoyancy by several pounds.

You can be a couple pounds light and still stay down by breathing towards the bottom of your lung capacity. So another possible strategy is to be neutral at 15', 500psi, full lungs; and neutral at 3 or 4', 0psi, and breathing shallow. With a 5mm full wetsuit, these are about the same for me.

IMO, if you can make a controlled ascent to the surface with a near empty tank, then you have enough weight, even if you need to change your breathing pattern a bit for the last 5' of the ascent. With this weighting, you should also be able to redescend by simply exhaling hard, even with a near empty tank.