Mar 032010
 

Estimating the Right Amount of Weights for Scuba Diving

perfect divers weight

Being properly weighted is one of the key elements in scuba diving. Through a few simple steps you can make your dive easier, longer and safer. Let’s run though the benefits of being properly weighted and how it’s done.

Being Underweight:

If you’ve underestimated the weights you need to carry, you may not know it at the beginning of the dive. As we dive, our tank becomes lighter due to our air consumption by as many as 2kg. An Aluminum Tank will be more buoyant throughout the dive and you may find it hard to stay underwater with an empty BCD. That means kicking downwards to stay underwater, and risking popping up to the surface in shallow water.

Being overweighted:

Over estimating the amount of weights you need is a much more common mistake. most divers prefer to or unknowingly carry more weights than needed. That creates a few problems and hazards:

1. Heavy weights (on a belt) drug the lower part of the buddy down, while an inflated BCD pulls the upper body up

A. You’re more likely to brush you fins or legs against the reef, or stir up the sand, thus risking yourself and damaging the environment.

B. Being less Hydrodynamic you increase drug and effort, wasting air which eventually leads to a shorter dive.

2. Having to inflate your BCD at depth means that you have to constantly adjust your BCD’s volume when changing depth, making buoyancy control harder. Air volume changes in the BCD pretty dramatically in the shallows, so you better not relay on a full BCD to support you in shallow water.

Bad Buoyancy- Not Using Your BCD Can Couse a Lot of Damage to the Environment

Example of Bad Buoyancy

How do we estimate the weights we need for our dive?

There are a few factors that contribute to our buoyancy when scuba diving:

1.Estimating weights needed with different exposure suits ( Salt Water):

Weight estimation lbs Weight Estimation kg Exposure Suit Type
  Add 0.5-2kg Add 4lbs Swimsuit or skin
About 5% Buddy Weight About 5% Buddy Weight 3mm one piece or shorty
About 10% Buddy Weight About 10 % Buddy Weight 5mm one or two piece
About 10% Buddy Weight + 4 to 5 lbs About 10% Buddy Weight  + 2kg  7mm two piece
About 10% Buddy Weight + 3 to 5 lbs About 10% Buddy Weight  + 1.5 to 2 kg Shell dry suit with light undergarment
About 10% Buddy Weight + 7 to 14 lbs About 10% Buddy Weight  +3 to 6 kg Shell dry Suit with heavy undergarment
Additional 2 lbs Additional 1 kg Add hood and boots

2. Estimating weights differences due to changes in water salinity:

Salt water is denser than fresh water. It simply has more particles in it. When moving from fresh water to salt water, with the same equipment, we tend to float and need to add weights according to this estimation:

Body weight Weights to add ( salt water)
100-125lbs/45-56kg 4lbs/2kg
126-155lbs/57-70kg 5lbs/2.3kg
156-186lbs/71-85kg 6lbs/3kg
187-217lbs/86-99kg 7lbs/3.2kg

3. Estimating weights changes due to tank/cylinder type:

We can choose to dive with tanks made of Aluminum (AL) OR Steel (ST), and in various volumes. Different tank types float differently. We want to be able to stay neutrally buoyant especially at the end of the dive, when our tanks are emptied and lighter.

Cylinder type and volume Weight change
AL80 + 4.4lbs/ 2kg
AL100 +3.0lbs/1.4kg
St HP80 -2.5lbs/1.1kg
St HP100 -1.0lbs/0.5kg
St HP120 0

Steel cylinders are heavier than Aluminum ones and don’t tent to float and contribute to your buoyancy when diving.

Once you’ve estimated the weights needed, its time to perform buoyancy check:

Remember, it’s recommended to perform a quick buoyancy check prior to diving after one of the followings:

1. You haven’t been diving for a while (gained a beer belly lately?)

2. Wearing new items or different equipment than those used before

3. Moving from fresh to salt water

5 step buoyancy check:

1. Enter the water fully equipped

2. At water to deep to stand in, empty your BCD fully.

3. Hold a normal breath, stay vertical and motionless

4. Add/subtract weight till you float at eye level following steps 1-3

5. Exhale and you should be able to slowly sink

Remember. Due to our air consumption our cylinders weigh 5lbs/2kgs less at the end of the dive. Add those extra weights prior to diving in order to be able to complete a safe and comfortable safety stop at the end of your dive.

PADI Advenaced Open Water Course- PPB

PADI Advanced Open Water Course- PPB. Improve your buoyancy

Weights estimation prior to scuba diving is an important step towards becoming a better, safer scuba diver. Estimating the right amount of weights for scuba is often neglected and both the diver and the environment are left to deal wit the consequences.

Once you’ve estimated and checked the weights you need for diving you’ll find it a lot easier to move about, saving air and getting closer to the reef without messing it all up. If you’re still struggling with your buoyancy, or use air way faster than you dive buddies, consider a pick performance buoyancy class to fine tune your buoyancy skills.

  10 Responses to “WEIGHT A MINUTE! ESTIMATING WEIGHTS FOR SCUBA DIVING IN A MINUTE”

  1. Your 7mm suit calulation is not clear and very confusing.
    please explain.

    Also was the first table for fresh water and then add the weight from the salt water table? Or was the salt water table for suit weighting a “stand alone” chart??

    PLease clarify

  2. Hi Dave
    I see what you’re saying, the numbers orders got mixed up here and I will fix it shortly.
    If you use a 7 mm wet suit, add 4-5 lbs or 2 KG to your 10% body weight worth of led,
    for example, if you were to weigh 70kg you’d have to carry about 9kgs (7+2). this is a fresh water calculation
    you would then have to add weight due to water salinity as mentioned in the next chart.
    You may also simply multiply the 1st chart result by 1.03 to be more precise.
    Remember, this is an estimation of the weights you’ll need, and you will still need to complete a buoyancy check prior to diving to fine tune your results.
    Hope this helps.
    Let me know if you need further instruction
    Tobi

  3. Hi I have had tremendous trouble with buoyancy over 40 dives. I use a full semi dry 7m suit + hood, gloves and boots-in Victorian open water. In addition, to make matters worse I have taken to wearing a 3mill Sharkskin vest. I do now pick up the problems of salt water and different tanks, so thanks for all this information.

  4. Hi Paul.
    I really hope these tips will help , let me know how you’re doing.
    Where is it you dive that requires so much coverage? is that BC?
    I’d love to see some photos and hear your story and how you come along with it.
    Please keep in touch
    Tobi

  5. Hi Tobi–for some reason I do not see any answer from you-tho you indicated you had commented. Neither did I get any personal mail from you.
    I live in Victoria Australia and dive in Port Phillip Bay (Google Dive Victoria Queenscliffe of Portsea center) We have dozens of good dives and many wrecks here within recreational limits. The water recently was about 12 degrees and I am 62 and usually work inside as a Masseur, Naturopath in heated conditions-therefore feel the cold. So this is why I use a Semi-dry wet suit of 7mil, plus a Sharkskin vest that I think is a bout 3 mill or more, boots, gloves and good. Where possible a 15 liter steel air/Nitrox tank, as the aluminium controls me frighteningly. This will be the area I will be doing diving 99% of the time in the indefinite future-outside the occasional trip away to Queensland (Six sleeps to go to an 8 day dive trip there) After this trip I am booked into a navigation course in September then a Stress and Rescue in October, followed by a Wreck course (tho dived on a dozen with supervised penetration already) Somewhere before Xmas I hope to find time to do a “Perfect Buoyancy’ course–but meantime I am fluctuating several meters at my safety stops–especially the 5-6 meter final one. It causes me to use up air quickly and spoil dives for others and work so hard that I lose some of my dive joy. Any and all tips for accurately estimating my needs under any situation –in simple terms if possible, will be very much appreciated. Will be taking camera along for first time this dive trip-so no idea how my head torch and hand torches might illuminate my targets.I will do a photography course next year and get some strobes once I know what I am doing. Thanks. Paul-Australia

  6. Hi paul,
    nice to hear from you.
    I’m sorry for the late replay, I’ve been to busy taking care of my first newborn son, didn’t bother with anything else, honestly.
    I guess my message didn’t go through. I have some questions for you:
    Is your gear relatively new? I’ve seen a lot of divers strugle with their gear ( wetsuits) over the first few dives. This is a bigger problem in shallow water, where bubbles trapped in your suit are inflated causing you to be more buoyant.
    Another issue suggested from what you describe here is you’re simply under weighted, which makes it difficult to stay naturally bouyant through the end of the dive.
    I would try a buoyancy check with an empty tank and full gear to see if that is the issue.
    please let me know it the buoyancy issues repeat throughout the whole dive or just at the very end.
    if you think non of these are the cases, please provide more details and I’ll get back to you.
    Thank You
    Tobi

  7. Hi I am new to diving with 40 dives under my weight belt. I have so much trouble with sudden descents, fast ascents, difficulty getting down and sometimes staying down, and heaps with my safety stops. I have figured out it is sometimes due to what tanks the dive company provide-aluminium or steel. I have resorted to requesting Steel 15 litre tanks so I can stay down with the teams or buddies, but on occasion I still come to the surface with nil or next to nil air,and on one occasion had to use the hang tank. I am not inclined to panic and try to breathe slowly and deeply etc. So believe it is mainly me fighting with y weights. I have done wreck, Nitrox and night diving and currently working towards master diver with navigation and stress and rescue for my specialties-and see the need to put in for ‘perfect buoyancy, and will when I can.
    Knowing all this and that my height is 5.7, my weight 80 kg and that I use a 15 litre steel tank of 32% when available, wear a sharkskin vest, gloves, boots, hood and 7 mill SEMI-DRY wet suit I wonder if from this information you can advise me what weights should work to start me off please. i will get in the pool next week pre my courses and try it out from there—-but I see that changing equipment, tanks, air remaining etc all contribute to weight needs.
    All help appreciated. Paul

  8. Hi. I see there was trouble with my computer not showing the replies above–now after doing a computer clean up Stuff is getting through.
    So thank you for the above replies, and congratulations of the birth of your firstborn, you will find these the best years of your life–until he becomes a teenager anyways! :>)
    Meantime in reply to your questions. My gear is 46 dives old, the water is in Port Phillip Bay Victoria Australia! About 12 -19 degrees in the water, plus I am 62 though I always have hated the cold.
    I was in Queensland 2 weeks ago and it was 23 degrees in the water which I loved and wore only a 5 mill suit-plus ALL the other clothes!
    As for being under-weighted. Most instructors tell me to wear about 10kg–but I have been using up to 13 kgs. On the other hand I have also had to use the BCD to inflate/deflate/inflate to keep my buoyancy. Safety stops are a nightmare-particularly with aluminium. you can write direct to my email if you would as I don’t always check back on all the sites I visit. regards Paul

  9. Hi Tobi,

    It would be great if you would clarify your table as Dave asked
    above. I’m really lost as to what: 14lbs/3-6kg – 7 +10% might
    mean. You use the minus sign for a range I think, you don’t
    specify which field is kg and which is pounds. Would it not be
    more simple to have a table with one field in kg and one in lbs?
    Would it not be easier to use the word ‘to’ rather an the – sign?
    You might also loose the kg or lbs completely and let your readers
    work out the conversion. It’s such a shame that this potentially
    useful page is just so cryptic.

    All the best,

    ===Rich

  10. Thanks Rich for your comments
    I had some technical issues with the tables, all sorted now, and I hope this make more sense now.
    Thanks again for your time and effort.
    Tobi

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