Adjusting Weight Before First Dives After OW Cert

[Litefoot]

I've been reading around the forum for the answer, but I still need help. When I certified in the Florida Keys, I wore a 3 mm shorty, an AL 80 tank and a Mares vest-style BCD. I used 3 lb weights in each vest pocket and a 2 lb weight on each side of the upper cam band for a total of 10 lbs in shot pouches. My buoyancy and balance were okay until we got to the safety stop on the last dive. I could not stay at 5m (which I contribute to the near-empty tank). My first dive after certification will be a 60' fresh water warm spring. Equipment configuraton: AL 80 tank, SG Paragon BP/W with aluminum backplate, 30 lb wing, and no wet suit.

My thinking is that in Florida, I might have added another 4-5 lb to compensate for the weight reduction of the consumed air. So maybe I needed 14 instead of 10 lb. Then I will lose some buoyancy going to fresh water, not wearing a wet suit and possibly with the different BC. I'm not looking for exact numbers, but can you give me a rough starting point for weighting based on what I've told you? Thanks!

 

[JoeTPhilly]

I've been reading around the forum for the answer, but I still need help. When I certified in the Florida Keys, I wore a 3 mm shorty, an AL 80 tank and a Mares vest-style BCD. I used 3 lb weights in each vest pocket and a 2 lb weight on each side of the upper cam band for a total of 10 lbs in shot pouches. My buoyancy and balance were okay until we got to the safety stop on the last dive. I could not stay at 5m (which I contribute to the near-empty tank). My first dive after certification will be a 60' fresh water warm spring. Equipment configuraton: AL 80 tank, SG Paragon BP/W with aluminum backplate, 30 lb wing, and no wet suit.

My thinking is that in Florida, I might have added another 4-5 lb to compensate for the weight reduction of the consumed air. So maybe I needed 14 instead of 10 lb. Then I will lose some buoyancy going to fresh water, not wearing a wet suit and possibly with the different BC. I'm not looking for exact numbers, but can you give me a rough starting point for weighting based on what I've told you? Thanks!

You will need less weight when not wearing a wetsuit and going to fresh water.

 

[inquis]

Going from salt to fresh, subtract 2.4% of total dry weight. You + tank (33 lb) is probably close enough. At 220 lb, it's a -6 lb adjustment for me (=253*0.024).

You were likely within 2 lb when you couldn't stay at your safety stop. That's a typical Expiratory Reserve Volume for adult male lungs. Any more and you would have been actively swimming down. Adjust by +2 lb.

Wetsuit is ballpark 2mm per mm thickness (full suit), so perhaps adjust by -5 lb for losing the shorty.

My Mares skeletonized alu BP/W is -1.5 lb buoyant. A non-skeleton is perhaps -2 lb. The previous jacket might be +1 to +3 lb (educated guess), so adjust by -3 lb (on the safe side).

I figure drop 6 lb for the equipment & suit with a further adjustment for salt.

 

[Cheizz]

I would do a proper weight check at the end of the dive to be more precise and for future reference. And keep in mind that any change in tank (material, size), water type (fresh/salt), or exposure suit will influence the lead you'll need. I have a small data sheet of all possible configurations I dive. I also pack a weight belt, just to be able to adjust, if needed (I dive a balanced rig as much as possible, no weight pouches for detachable weights).

 

[JoeTPhilly]

I've been reading around the forum for the answer, but I still need help. When I certified in the Florida Keys, I wore a 3 mm shorty, an AL 80 tank and a Mares vest-style BCD. I used 3 lb weights in each vest pocket and a 2 lb weight on each side of the upper cam band for a total of 10 lbs in shot pouches. My buoyancy and balance were okay until we got to the safety stop on the last dive. I could not stay at 5m (which I contribute to the near-empty tank). My first dive after certification will be a 60' fresh water warm spring. Equipment configuraton: AL 80 tank, SG Paragon BP/W with aluminum backplate, 30 lb wing, and no wet suit.

My thinking is that in Florida, I might have added another 4-5 lb to compensate for the weight reduction of the consumed air. So maybe I needed 14 instead of 10 lb. Then I will lose some buoyancy going to fresh water, not wearing a wet suit and possibly with the different BC. I'm not looking for exact numbers, but can you give me a rough starting point for weighting based on what I've told you? Thanks!

You might want to take a look at this link Estimated Diving Weight Calculator | DiveBuddy.com or the peak buoyancy spreadsheet that is on this site.

 

[inquis]

You can also go from first principles. I have a list of component buoyancies -- weights when submerged and a luggage scale is handy for this -- I've measured over time. I'm slightly negative in a bathing suit (will sink at the end of a normal exhale), so I call that 0 for simplicity. An AL80 tank & reg in fresh water is +1.5 lb. My BP/W measured at -1.5 lb. Reserve air (what you'll have at the end of the dive) is -1 lb (500 psi AL80 or 12.5 cuft air). Fins are neutral. Adding all that up, I get -1 lb net buoyancy (no lead required).

The largest uncertainty is your personal buoyancy. If you have access to a pool or even hot tub to ballpark that, it would be helpful.

 

[inquis]

+1 on the buoyancy calculator here on SB (a comprehensive spreadsheet). The simple online calculators are way off in my experience (typically suggesting way too much lead).

 

[James79]

I've been reading around the forum for the answer, but I still need help. When I certified in the Florida Keys, I wore a 3 mm shorty, an AL 80 tank and a Mares vest-style BCD. I used 3 lb weights in each vest pocket and a 2 lb weight on each side of the upper cam band for a total of 10 lbs in shot pouches. My buoyancy and balance were okay until we got to the safety stop on the last dive. I could not stay at 5m (which I contribute to the near-empty tank). My first dive after certification will be a 60' fresh water warm spring. Equipment configuraton: AL 80 tank, SG Paragon BP/W with aluminum backplate, 30 lb wing, and no wet suit.

My thinking is that in Florida, I might have added another 4-5 lb to compensate for the weight reduction of the consumed air. So maybe I needed 14 instead of 10 lb. Then I will lose some buoyancy going to fresh water, not wearing a wet suit and possibly with the different BC. I'm not looking for exact numbers, but can you give me a rough starting point for weighting based on what I've told you? Thanks!

I use the rsingler's Buoyancy calculator that @inquisit referenced. I work it from both ends, though... figure out your personal buoyancy, then use best estimates on the rest. Then good buoyancy checks at the end of dives help you refine it. For example, if you know your personal buoyancy and the calculator gives you a number for your BPW, no wetsuit, freshwater configuration that you then dive, you can see how far off it is. Since the tank characteristics are a known, your personal buoyancy is a known, and you have no wetsuit, you can attribute the difference to errors in your assumptions on your BPW characteristics and refine that estimate. I used this apporach refining it over the course of a few dive scenarios (salt vs. fresh, shorty vs. fullsuit vs. no suit, etc.) and now I can just plug in different conditions (or new gear like different wetsuits) with the knowns for the rest of my gear and consistently get results within a pound of what I need.

Respectfully,

James

 

[Litefoot]

Going from salt to fresh, subtract 2.4% of total dry weight. You + tank (33 lb) is probably close enough. At 220 lb, it's a -6 lb adjustment for me (=253*0.024).

You were likely within 2 lb when you couldn't stay at your safety stop. That's a typical Expiratory Reserve Volume for adult male lungs. Any more and you would have been actively swimming down. Adjust by +2 lb.

Wetsuit is ballpark 2mm per mm thickness (full suit), so perhaps adjust by -5 lb for losing the shorty.

My Mares skeletonized alu BP/W is -1.5 lb buoyant. A non-skeleton is perhaps -2 lb. The previous jacket might be +1 to +3 lb (educated guess), so adjust by -3 lb (on the safe side).

I figure drop 6 lb for the equipment & suit with a further adjustment for salt.

Thank you! That's a very detailed and extremely helpful answer. So it looks like I may not need any lead if I'm figuring this all correctly, at least as a starting point.

But if I then do a weight check (empty BC, inhale, eyes level with water) and I'm where I need to be, is it proper to then add a few pounds to account for the consumed air at the end of the dive. At least that is what I was pondering after my safety stop experience in Florida.

Thanks James. That sounds like a very thorough and methodical way of getting it right. And it's repeatable.

 

[James79]

Thank you! That's a very detailed and extremely helpful answer. So it looks like I may not need any lead if I'm figuring this all correctly, at least as a starting point.

But if I then do a weight check (empty BC, inhale, eyes level with water) and I'm where I need to be, is it proper to then add a few pounds to account for the consumed air at the end of the dive. At least that is what I was pondering after my safety stop experience in Florida.

Perfect world to nail down Buoyancy is to do buoyancy and trim checks with a near empty tank. Easier alternative is to do them with a full tank, then add a few pounds to account for consumed air at the end of the dive (as you suspected). 65 cubic feet of air is about 5 lb. So a full tank weight check where you can just hold at 15 ft. with no air in your wing/BCD you would add 5 lb and expect to be able to hold your safety stop at the end of a dive no problem.

Respectfully,

James