Buoyancy question

[Paladin]

As some of you already know, I did not own or use a BC or wetsuit until about 3 years ago. I was finally dragged, kicking and screaming, into modern style diving and bought a 3mm wetsuit and a couple of BCs (a jacket and a horse collar). Now, when I was diving without a wetsuit or BC, I used no weight when diving my old steel 72 and 4 pounds when using my AL80. Adding a 3mm wetsuit and a BC, I found I need 12 pounds of lead with a steel 72 or 16 pounds with an AL80 to feel right. By that I mean that I like to be slightly negative at the surface at the beginning of the dive and slightly positive at the surface at the end of the dive.

Last year, I got a 5mm wetsuit for colder, deeper dives in our mountain lakes. I expected to need an additional 4 to 6 pounds of lead to compensate for the extra buoyancy, based on various articles which claimed that wetsuits add either 2 or 3 pounds positive buoyancy per millimeter of thickness. What I actually need, it turned out, is only an extra two pounds to feel right in the water.

Using double steel 72s, I need 6 pounds with a 3mm and 8 pounds with a 5mm.

I am just wondering if this marginal, 2 pound difference in buoyancy between 3mm and 5mm suits is typical or if, as usual, I am an oddball.

 

[Texasguy]

A noob here. A bit off topic question. How does one hold buoyancy without a wing or BC? Seems like unless you get weights exactly for neutral buoyancy, you will spend time fighting (to a small or a large degree) to stay at a certain depth as your tanks shift weight. Thus, how would you make adjustments to buoyancy though out the dive? ...by picking up some stones at the bottom?
...or do you overweight yourself and then constantly adjust your depth as you sink bit by bit?

PS: What is a "horse collar" BC configuration?

 

[Scuba_Noob]

I assume that you maintain buoyancy with good breathing techniques and very exact weighting.

Horse collar BC: http://anonytron.com/Scuba/SeaTecHorseCollar.jpg

 

[g1138]

Do you need to pike dive to descend? Not by habit but actually need to do a skin dive of some sort?

If so then I think
1) your old habits are still present.
2) you're lightly weighted and could use more.

That's not to say you don't need the weight. But you could add more and not be grossly overweighted. Nothing wrong with what you're doing if you feel your dive is still safe and fun.

I weight myself so at the beginning of my dive, a full exhale and a 3 second wait is what it takes for me to sink and gain momentum on my descend. Most of my friends are weighted heavier so if they were to breath in, they'd still be sinking.
If I were to breath in within those 3 seconds, I would pop back up to the surface. I fix this by back kicking to 3 ft, then bending over to a head down position. I'm kinda an oddball too.

 

[Paladin]

A noob here. A bit off topic question. How does one hold buoyancy without a wing or BC? Seems like unless you get weights exactly for neutral buoyancy, you will spend time fighting (to a small or a large degree) to stay at a certain depth as your tanks shift weight. Thus, how would you make adjustments to buoyancy though out the dive? ...by picking up some stones at the bottom?
...or do you overweight yourself and then constantly adjust your depth as you sink bit by bit?

PS: What is a "horse collar" BC configuration?

There have been a bunch of threads on the topic, especially over in the "Vintage Equipment" forum:

http://www.scubaboard.com/forums/basic-scuba-discussions/167633-vintage-divers-no-bc.html

 

[g1138]

A noob here. A bit off topic question. How does one hold buoyancy without a wing or BC? Seems like unless you get weights exactly for neutral buoyancy, you will spend time fighting (to a small or a large degree) to stay at a certain depth as your tanks shift weight. Thus, how would you make adjustments to buoyancy though out the dive? ...by picking up some stones at the bottom?
...or do you overweight yourself and then constantly adjust your depth as you sink bit by bit?

PS: What is a "horse collar" BC configuration?

You weight yourself for your planned max depth. Below that max depth you're negative, above you're positive. If you deviate you'll have to compensate by swimming higher, or picking up stones.
Your bouyancy is controlled all in your lung power, and your dive begins with a textbook pike dive and swim to your max depth.
You're pretty much relegated to square profiles; but you feel a whole lot more freedom and less encumbered.
Back in the day this was why skin diving and scuba diving were interchangeable terms.

Horse collar BC's are basically airline life jackets, but made specifically for scuba. They're shaped like a horse collar and sit on you like a bib.
Some have power inflators, other's CO2 cartridges that are meant to be used on the surface only. Most are oral inflators.

 

[Paladin]

Do you need to pike dive to descend? Not by habit but actually need to do a skin dive of some sort?

If so then I think
1) your old habits are still present.
2) you're lightly weighted and could use more.

That's not to say you don't need the weight. But you could add more and not be grossly overweighted. Nothing wrong with what you're doing if you feel your dive is still safe and fun.

I weight myself so at the beginning of my dive, a full exhale and a 3 second wait is what it takes for me to sink and gain momentum on my descend. Most of my friends are weighted heavier so if they were to breath in, they'd still be sinking.
If I were to breath in within those 3 seconds, I would pop back up to the surface. I fix this by back kicking to 3 ft, then bending over to a head down position. I'm kinda an oddball too.

I weight myself to be slightly negative near the surface at the beginning of a dive. Breathing normally, I sink slowly for the first 3 to 5 feet. I usually do pike dive at first to speed things up but I can descend without doing this, just a lot slower. At the end of the dive, I am slightly positive and can use a snorkel without adding air to my BC.

---------- Post added March 20th, 2013 at 11:50 PM ----------

I assume that you maintain buoyancy with good breathing techniques and very exact weighting.

Horse collar BC: http://anonytron.com/Scuba/SeaTecHorseCollar.jpg

Getting my weight as precise as possible is an old habit I learned back in the 1960s.

 

[g1138]

I weight myself to be slightly negative near the surface at the beginning of a dive. Breathing normally, I sink slowly for the first 3 to 5 feet. I usually do pike dive at first to speed things up but I can descend without doing this, just a lot slower. At the end of the dive, I am slightly positive and can use a snorkel without adding air to my BC.

Sounds fine to me. How's your ascent rate at the last 10 ft? I usually have to control my breathing a lot to keep from corking above 8ft.
At 8 ft, fully deflated BC, anything at an ambient breath or above sends me on an ascent. If I'm doing a real shallow dive, I usually add 2-4 lbs because of this.
I think you might be in the same boat.

 

[Paladin]

You weight yourself for your planned max depth. Below that max depth you're negative, above you're positive. If you deviate you'll have to compensate by swimming higher, or picking up stones.
Your bouyancy is controlled all in your lung power, and your dive begins with a textbook pike dive and swim to your max depth.
You're pretty much relegated to square profiles; but you feel a whole lot more freedom and less encumbered.
Back in the day this was why skin diving and scuba diving were interchangeable terms.

Horse collar BC's are basically airline life jackets, but made specifically for scuba. They're shaped like a horse collar and sit on you like a bib.
Some have power inflators, other's CO2 cartridges that are meant to be used on the surface only. Most are oral inflators.

My horse collar was bought new around three years ago and has an LP power inflator and a CO2 inflator. I plugged off the CO2 fitting.

---------- Post added March 20th, 2013 at 11:59 PM ----------

Sounds fine to me. How's your ascent rate at the last 10 ft? I usually have to control my breathing a lot to keep from corking above 8ft.
At 8 ft, fully deflated BC, anything at an ambient breath or above sends me on an ascent. If I'm doing a real shallow dive, I usually add 2-4 lbs because of this.
I think you might be in the same boat.

Yep. Starting at about 8 feet, I have to watch my breathing a little more closely. I don't actually cork, but it's difficult to swim horizontally above, say, 8 to 10 feet. It's very rare that I am diving that shallow but if I know that's where I'm going to be, all I have to do is slip a two pounder into a pocket to compensate.

My question is, is it normal for there to be only a two pound buoyancy difference between a 3mm suit and a 5mm suit?

 

[g1138]

My question is, is it normal for there to be only a two pound buoyancy difference between a 3mm suit and a 5mm suit?

Oh right, sorry; been beating around the bush. No, it's a bit uncommon in my experience.
You could do a dunk test in a large trash can to see if that's the actual bouyancy difference between the two suits. But I'd be very surprised if it actually came out to 2 pounds. I'm thinking 5lbs minimum is the norm, but my experience is limited.