Scuba Buoyancy Masterclass Series #4
PERFECT SCUBA WEIGHTING
by Andy Davis, PADI TecRec, ANDI, BSAC and SSI Technical Diving Instructor
Divers seeking perfected scuba buoyancy can achieve precise and correct weighting through the application of several assessment methods. As the diver progresses in experience, whenever they change equipment or whenever they change diving environments (salt/fresh water) they should re-assess their weighting. During initial stages of diver development, changes in breathing patterns and increased relaxation underwater often also allows a slow progressive reduction in weights.
Perfect weighting means perfect relaxation
Our aim is to carry sufficient weight to allow us to maintain neutral buoyancy at any stage in the dive, without carrying excess weight that has to be off-set by adding extra air to our BCDs. At the very most, we need sufficient weight to allow us to maintain neutral buoyancy at the end of the dive, when our exposure suits re-gain buoyancy on ascent and we have depleted a significant weight of gas from our scuba cylinders. This is essential if we are to maintain safety stops and conduct a slow, controlled ascent from that stop to the surface.
There are three primary methods for estimating, assessing and confirming our weighting requirements:
1) Basic Weighting Guidelines
-Estimate- We can follow a series of basic calculations, which incorporate the buoyancy of our exposure suit and body size to provide a rough estimate of our weighting needs (see below). This allows us to set-up a weight belt in advance of our dive.
2) Pre-dive Weight Check
-Assess- Once we actually enter the water, we can confirm that our estimation was correct. This check ensures that we have sufficient weight to descend, but are not carrying surplus, unnecessary weight. It is a simple, quick check that can be conducted before any dive. To carry out this check, conduct the following steps:
- At the surface, take a deep breath and hold it.
- Cross your ankles to prevent any instinctive fin movement (upwards propulsion).
- Keep your arms against your body to prevent any instinctive sculling.
- Hold your LPI vertically upwards and release all the air from your BCD.
- You should now float at approximately eye-level in the water.
- Exhale the breath that you were holding.
- You should now begin to slowly sink.
- If not, then add/remove weight until you do float at eye level whilst holding a normal breath and can sink when you release that breath.
- Once this is achieved, add 1-2kg of weight to account for air use during the dive.
3) Shallow-Water Weight Check
-Confirm- Whilst the pre-dive weight check gives us a fair idea of our weighting requirement, it does not account for air use during the dive. It is well worth conducting an accurate check that absolutely confirms your weighting requirement under these circumstances. To conduct a weight confirmation, follow these steps;
- Attempt to hover neutrally buoyant at 3-5m depth, whilst breathing normally.
- Deplete the air in your cylinder to 30bar.
- Slowly reduce the weight that you are carrying (small weights are best, for fine tuning).
- When you reach a stage that requires breathing adjustment (shallow breathing) to maintain your stop depth, then you have reached your absolute minimum weighting.
Once you confirm your minimum weighting requirements, you can be confident that you will have enough weight for your initial descent, and enough weight to hold a safety stop with minimum air remaining in your cylinder. Nothing more, nothing less. Your progress towards effective buoyancy now has a strong foundation and will be considerably easier.
PADI – BASIC WEIGHTING GUIDELINES
Basic weight estimation for an average build diver in salt water — decrease weight for lean body type and increase for heavier.
PADI Basic Weighting Guidelines
In order to compensate for an expected loss of weight, caused by the consumption of air from the scuba cylinder, it is also necessary to add 2-4lbs of weight to the total amount calculated.
(Adventures in Diving Manual, PADI, 2001, p.213)
For accurate details of scuba cylinder buoyancy change: please see the Luxfer Scuba Cylinder Buoyancy Specifications.
Next article: ‘Trim and Positioning’
Previous Articles:
Scuba Buoyancy Masterclass 1of9 – Buoyancy Control for Scuba Divers
Scuba Buoyancy Masterclass 2of9 – The Need for Buoyancy Control
Scuba Buoyancy Masterclass 3of9 – Achieving Great Buoyancy Control
« No.3 | Achieving Great Scuba Buoyancy Control No.5 | Precision Trim & Position Contol »
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[...] by DevonDiver on Today at 03:16 AM (Scuba Tech Philippines – Scuba Blog) [h=1]Assessing Your Weight Requirements [/h] Divers can achieve precise and correct weighting through the application of several assessment [...]
[...] Next article: ‘Assessing Your Weight Requirements’ [...]
[...] Blog Entries8 Originally Posted by Antagonist I am currently weighted at 16 lbs. I am 6'0 195lbs. This weekend my wife and I went diving and one of my weight pouches gets ripped out while taking pictures during our dive. The only way I noticed it is because I started to roll to my left. I went up to the surface and was able to go back to the bottom to look for it with no problem. But my wife is weighted with 14 lbs and has a problem going down. She is 5'4" 130lbs. I am confused, can someone enlighten us? (Also I am purchasing new BCDs for my wife and I. Weight integrated BCD weights gets ripped out or to much room for human error BP&W is what's next for us and the plastic zippers and breaking to much on weight pouches. To expensive in japan!!) Losing 1/2 your weight, and still being able to easily re-descend, does indicate that you are over-weighted. At what stage in the dive did you lose the weights? More relevant: how much air remained in your cylinder at that time, and at what depth were you? Whether you cylinder was full, or empty, would make a difference to the impact of losing the weight.. as the air in your tank has a weight value. Likewise, the depth is a factor, as this will determine the relevant buoyancy provided by your exposure suit. The cast-iron test for weighting is whether you can maintain a hovering safety stop, with minimum reserve air in your cylinder. This means that your exposure suit is at its most buoyant and your cylinder weighs the least. If you can maintain the stop, then you have enough air. On that stop, assess how much air you have in your BCD. You shouldn't really need any air in that scenario. If you have air in your BCD, then remove weights from your rig, until you reach the limit at which you can comfortably maintain your hover. That will be perfect weighting. Problems with descent, in novice divers, are often linked with either; failure to fully deflate the BCD, anxiety causing heavier breathing (inflated lungs add buoyancy), not fully exhaling and/or subconsious movement of the feet (fining, whilst vertical) which provides upwards thrust. I'm in the middle of writing a series of blog articles on buoyancy and weighting at the moment; you may find them useful: Scuba Buoyancy Masterclass 4of9 – Assessing Your Weight Requirements [...]
[...] Dives200 – 499 DevonDiver – Just want to say thanks for the blog. I personally believe that buoyancy is the MOST important skill and I work on it everytime I dive. It's nice to read your blog an pick up on the finer techniques that have passed me by. Rich Originally Posted by DevonDiver Losing 1/2 your weight, and still being able to easily re-descend, does indicate that you are over-weighted. At what stage in the dive did you lose the weights? More relevant: how much air remained in your cylinder at that time, and at what depth were you? Whether you cylinder was full, or empty, would make a difference to the impact of losing the weight.. as the air in your tank has a weight value. Likewise, the depth is a factor, as this will determine the relevant buoyancy provided by your exposure suit. The cast-iron test for weighting is whether you can maintain a hovering safety stop, with minimum reserve air in your cylinder. This means that your exposure suit is at its most buoyant and your cylinder weighs the least. If you can maintain the stop, then you have enough air. On that stop, assess how much air you have in your BCD. You shouldn't really need any air in that scenario. If you have air in your BCD, then remove weights from your rig, until you reach the limit at which you can comfortably maintain your hover. That will be perfect weighting. Problems with descent, in novice divers, are often linked with either; failure to fully deflate the BCD, anxiety causing heavier breathing (inflated lungs add buoyancy), not fully exhaling and/or subconsious movement of the feet (fining, whilst vertical) which provides upwards thrust. I'm in the middle of writing a series of blog articles on buoyancy and weighting at the moment; you may find them useful: Scuba Buoyancy Masterclass 4of9 – Assessing Your Weight Requirements [...]
[...] The Need for Buoyancy Control Scuba Buoyancy Masterclass 3of9 – Achieving Great Buoyancy Control Scuba Buoyancy Masterclass 4of9 – Assessing Your Weight RequirementsShare ThisTweetFacebookLinkedInStumbleUponDiggDeliciousScuba Buoyancy Masterclass 2of9 – The Need [...]
[...] Buoyancy and Weighting Posted on July 14, 2011 by Scuba Tech Philippines When scuba divers calculate their buoyancy with an aluminum cylinder, it is essential for them to know the relative buoyancy characteristics [...]