BC full or not - Split from overweight

[Walter]

I guess you need to qualify where you are diving b/c here on the big lakes nobody goes in the water and strait down.

Viz is not always optimum here in Panama City either, and sometime we have a bit of current to deal with. We decend and acend on the anchor line or tie in and usally have to swim to it after entry.

That may be true for where you are but it is not true for this area. Here in the Great Lakes it isn't unusual to have your boat tied to the back of another boat and have 2 granny lines to follow to the mooring ball/down line. We also tend to have a pretty good current so you would be so far off the wreck by the time you got to the bottom the dive would be pooched.

Actually, I've dived the Great Lakes (admitedly limited experience there) and Panama City. I've also dived wrecks in other areas with stronger currents and lower viz than I've personally encountered in either place. I'm also familiar with tag lines (granny line is a horrible term), I've been rigging tag and current lines for decades and using them even longer. They are easier to use with no air in your BC. Inflate your BC if you want, but if you are properly weighted, there's no need even if you want to hang out on the surface a spell.

 

[jtivat]

Actually, I've dived the Great Lakes (admitedly limited experience there) and Panama City. I've also dived wrecks in other areas with stronger currents and lower viz than I've personally encountered in either place. I'm also familiar with tag lines (granny line is a horrible term), I've been rigging tag and current lines for decades and using them even longer. They are easier to use with no air in your BC. Inflate your BC if you want, but if you are properly weighted, there's no need even if you want to hang out on the surface a spell.

Well I don't know what your Great Lakes dives were but most mine are deep and I carry 28LBS. of air in my tanks. I need some air in my wing at the start of a dive to stay a float (and that is weighted so my wing is empty at my last deco stop and the dry suit is squeezing just a touch). Besides what is the problem with having some air in the BC the higher out of the water the better IMO.

 

[Walter]

jtivat, that's an atypical situation. Very few divers carry 375 cu ft of air on a dive. If you've added just enough air to your BC to compensate for the extra 300 cu ft of air you're carrying, you've done essentially the same thing I recommended to folks with a single tank. If you want to use your wing as a boat, go ahead, I really don't care. I do disagree with the concept of "the higher out of the water the better" as it merely displays a lack of confidence.

 

[Charlie99]

Well I don't know what your Great Lakes dives were but most mine are deep and I carry 28LBS. of air in my tanks. I need some air in my wing at the start of a dive to stay a float

I can see why you need some air in your wing at the start of the dive. Your load of 375 cubic feet is much more than what the typical diver carries.

edit: Walter is faster at typing.

 

[Walter]

Well, at least our math is right (or we made the same mistake).

 

[Charlie99]

Well, at least our math is right (or we made the same mistake).

It looks like we both used the precise figure of 0.0745 lbs per cu ft at 70F and sea level.

The approximation of 6 pounds per 80 cubic feet is close enough for practical purposes, which in turns works out nicely to about 1 pound per 500psi in an AL80.

That's a handy number for doing weight checks with other than a near empty tank.

If a single tank diver, with a reasonable amount of air in their tank(i.e., NOT 375cu ft) has done a weight check and adjusted properly, then they aren't going to be worried about putting a whole bunch of air into their BCDs before jumping in.

 

[Kingpatzer]

As a relative new diver, I have to ask:

WHY do some people consider it a bad idea to be significantly positively bouyant on entry?

Again, as a relative newb, it seems to me that entry is one of the most dangerous actions a diver takes -- you can hit your head on something in the water that you didn't see, you can lose your reg, or any other number of things can go wrong which could create a problem.

It strikes me that having air in the BC is a reasonable safety precaution against those eventualities (rare as they may be).

Having air in the BC at entry doesn't mean you decend with a BC full of air, and doesn't mean you're over-weighted. It just means you're making sure that you will stay at the surface so that the boat and your buddy can verify that everything is ok.

Why is that a bad practice?

 

[jtivat]

jtivat, that's an atypical situation. Very few divers carry 375 cu ft of air on a dive. If you've added just enough air to your BC to compensate for the extra 300 cu ft of air you're carrying, you've done essentially the same thing I recommended to folks with a single tank. If you want to use your wing as a boat, go ahead, I really don't care. I do disagree with the concept of "the higher out of the water the better" as it merely displays a lack of confidence.

380 was my number and a rounded a bit on the math but I don't think that I lack confidence b/c I like to be out of the water a bit but who knows maybe I do.

 

[Charlie99]

As a relative new diver, I have to ask:

WHY do some people consider it a bad idea to be significantly positively bouyant on entry?

I don't see it as a BAD practice. It's just not necessary.

When I see someone on a boat pushing their inflator until the overpressure dumps trip, I watch them very carefully. Many BCDs will squeeze a person when fully inflated. Some will tend to pitch them forward. Most of all though, it may be a sign of someone who is very nervous about entering the water.

My other point is that, having to put a signficant amount of air into your BCD in order to stay on the surface is an indicator of being overweighted.

Even if you weight yourself towards the heavy side, such that you can hold easily hold a safety sto right at 1' of depth with a completely empty tank, you will be negatively buoyant only by the weight of the air in your tank --- which is about 6 pounds for each 80 cubic feet. In addition, when you first get in, you have various air pockets in your wetsuit, and unless your wetsuit is already saturated, it will have some extra buoyancy for the first few minutes.

BCDs are not life preservers. Having extra air in your BCD isn't going to keep your face out of the water if you hit your head and go unconscious.

Adding lots of air to your BCD isn't bad. It's just not needed for someone properly weighted.

 

[Walter]

Again, as a relative newb, it seems to me that entry is one of the most dangerous actions a diver takes -- you can hit your head on something in the water that you didn't see, you can lose your reg, or any other number of things can go wrong which could create a problem.

If there's a chance of hitting your head (or any other body part) on something you can't see, you need to choose a different entry method. An inflated BC will not stop you from hitting something. If you lose your reg, you weren't holding it it. You should be holding it in. You should also be able to both recover your primary and pick up your octo with ease.

Having air in the BC at entry doesn't mean you decend with a BC full of air, and doesn't mean you're over-weighted. It just means you're making sure that you will stay at the surface so that the boat and your buddy can verify that everything is ok.

The only reason to inflate your BC prior to entry is to compensate for being significantly overweighted. If you are not significantly overweighted, you will have no problem staying afloat to signal to the boat and to get together with your buddy with a fully deflated BC.