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I think I use too much weight when scuba diving, how much do I need..?
This article was written to help answer just that. Whether you’re a new diver or an advanced/technical diver, this article will leave you with a better understanding of what weight you’ll need for the types of diving you will be doing. Within this article I’ll be discussing what effects your buoyancy and the amount of weight you’ll need, what lift capacity will your BCD needs, where to put the weights you’ll need and finally how to and how often you should conduct a buoyancy check.
"Adjust the weight so that the student floats at eye level with an empty BCD whilst holding a normal breath" this is the performance requirement a PADI instructor must follow during your open water diver course.
It is disappointing to see many "seasoned" scuba divers and dive professionals are still diving overweighted. Please take a look at this short video (to the left). It shows a diver in a 3/5mm wetsuit diving in salt water wearing so much weight that he is unable to alter his trim, resulting in the diver practically swimming vertically. Luckily enough for him, this was a slow drift dive where not much finning was needed.
As for a diver’s trim, you should aim to be as flat as possible while submerged, similar to a sky diver whilst free falling.
What effects the amount of weight you need..?
Fresh or salt water – In salt water it’s normal to need slightly more weight than in fresh water.
Exposure suits -The thicker the wetsuit e.g 3mm or 7/5mm, the more weights you will need. Generally more weight is needed for dry suits than with wetsuits.
BCD capacity size - The bigger or more lift your BCD or wing has, the more weight will be required eg; a dual bladder BCD will need slightly more weight than a standard BCD.
Steel or Aluminum Cylinder(s) - Generally all cylinders start negatively buoyant. Steel cylinders become neutrally to negatively buoyant when used and aluminum cylinders become positively buoyant when used.
Your body mass – Generally the higher your BMI, the more weight you will need.
If any of the above factors change, I suggest you conduct another buoyancy check as outlined below. See here for a useful cylinder buoyancy calculator. This will give you a general idea of what extra weight you may or may not need, as it shows you how different manufacture’s cylinders have different buoyancy characteristics.
How much weight do I need and what's a buoyancy check..?
As each individual person has a different natural buoyancy, you’ll need to test whether you naturally sink or float. You can actually try this in the comfort of your own swimming pool. You are trying to find out whether you naturally sink or float. To test this out, you must enter the water wearing just your swimming suit/costume. The water needs to be a little deeper than your body height. Then do the following three things while keeping your body still and relaxed; 1. Hold a full breath 2. Hold a normal breath (approx half) and 3. Hold once you breathe completely out. This is called a buoyancy check. The results from theses three simple steps will tell you whether you’re naturally a floater, sinker or neutrally buoyant person.
Neutral person - They are able to hold a full breath and float with their head out of the water. Whilst holding a normal breath they are able to float, with the water at eye level. Finally when they breathe all the way out, they will start to sink. Once their lungs are completely empty, they will continue to sink to the bottom. This is the ideal person for scuba diving and would need only an average amount of weight while diving fully equipped.
Buoyant person - When holding a full breath they tend to float with their head and shoulders out of the water. Whilst holding a normal breath, they are still able to float comfortably. Lastly they breathe out completely and still find that they float or maybe now around eye level. This person will require however many weights it takes to make them similar to the "Neutral person".
Negative person – When holding a full breath they find that they just float at eye level. As they hold a normal breath they now sink below the water. When they breathe out completely, they sink quite fast in a swimming pool. This person will probably not need much weight to scuba dive at all, depending on the chosen exposure suit. Usually this person would don a 3mm wetsuit and would be similar to the ‘Neutral person’.
Adding an exposure suit will add buoyancy throughout your body. To find out the correct amount of weight for your exposure suit, you will need to don your exposure suit and primary accessories eg; fins, mask and snorkel. Enter the water (sea/lake) and repeat the exercise above. For the first buoyancy check with a new or different suit, I suggest you wear a weight belt that has multiple pockets on it. They are great as they enable you to add weight in small increments. Once you know the exact weight that you require, you can transfer the correct amount of weight to your BCD weight integrated pockets. Continue adding weight until you find the amount that enables you to float at eye level whilst holding a normal breath. When you breathe in you’ll float and when you breathe out you’ll sink. If all goes well, you now have the correct weight for snorkeling and allows you to skin dive.
With scuba diving, two things will change constantly throughout your dive. Firstly is the weight of the air in your cylinder, as you consume air your cylinder becomes more buoyant (see here a video showing how cylinders become more buoyant). Secondly is the weight of the water around you. The deeper you go the less buoyancy you have, so you need to add more air to your BCD. Therefore its important you carry the correct amount of weight and have the right equipment for the types of diving you are doing.
The next important thing you need to understand is how you should be at the end of your dive. The ideal scenario would be a diver who has between 30-50 bar of air still in their cylinder(s) and an almost empty BCD. This diver would be able to continue breathing normally and stay comfortably neutral at 3 metres. If you were over weighted, you would not be able to hold this depth due to the fact that you would have had to compensate your negative buoyancy by having an excessive amount of air in your BCD. If that BCD then failed, you would most likely sink or have to exert yourself by kicking hard to maintain in position at that shallow depth.
What lift does my BCD need..?
As this article is designed to accommodate everyone, let me quickly explain what a BCD is to those of you who do not know. A BCD is your buoyancy compensating device and it does exactly that. As you dive deeper, you’ll need to add enough air to either slow your decent or to stop completely neutral (hover). When ascending it does the opposite, you expel air to maintain a safe ascent.
In regards to how much lift should your BCD have, really depends on what type of diving you are doing and what exposure suit you are wearing. If you are wearing a drysuit rather than a wetsuit, it means that you will need to put less air into your BCD as you dive. This is due to the air trapped within your drysuit. However if your drysuit floods, you will need sufficient lift within your BCD to support you at your deepest depth. Also your exposure suit will now become more negative due to the flooding and lack of air surrounding your body. Most dive centres should be able to advise you on what is suitable. There are currently many BCDs on the market that, in my opinion, have way to much lift.
If a BCD has too much of a lift capacity, you’ll find that the air moves around within the bladder as you dive. This can result in making it difficult for you to expel air when you need to. You will also find that these BCDs or wings are generally very bulky. When buying a BCD, I like to use the ‘KISS’ principle; "KEEP IT SUPER SIMPLE". What this basically means is if you don't need it, then why have it. If you want to find out my opinion on dual bladder BCD's or technical diving wing systems, please feel free to contact me via email.
Why should I dive with the correct weight..?
Diving with excess weight is unfortunately very common. So why do some divers still continue to do it? The most likely reason is that not enough time was spent on finding the correct weighting during their initial diver training. These people continue to scuba dive over-weighted and usually say they need that extra weight, "just in case". Some instructors may dive with some extra weight for the sole reason that once they are in the water, they can hand off small amounts to their divers, if they should become more buoyant during the dive. This practice is OK for most instructors as they have a high experience level and can easily cope with a little extra weight. If they were to encounter a problem eg; BCD failure, they’re able to, through their training, balance the additional weight. I personally do not carry any extra weight, however I used too. Now I choose to spend more time working with my divers to get their weight and buoyancy through breathing control correct. This gives them a complete understanding of buoyancy, sometimes before we even enter the water. Basically, I start with everything that is mentioned in the article.
Through this practice I have found that the extra time I spend working on a diver’s buoyancy really does pay off, the students go on to further their education as diving becomes more enjoyable for them much sooner.
As a diver, you need to be able to select the right kind of exposure suit based on the water temperature and planned dive/snorkel duration (more time underwater = the colder you get). Once you have chosen your exposure suit, you then need to find out how much weight it takes to make that specific suit neutral. You can do this by donning your suit and repeating the buoyancy check as above and then making a note of the exact amount of weight. You now have the correct weight for snorkeling and skin diving, whilst wearing your selected exposure suit.
When you put on your BCD and cylinder, you will once again need to readjust the amount of weights you’re using. Remember if you’re using a aluminum tank, you will most likely require slightly more weight than a steel cylinder. You will need to actually test this. If you have a cylinder that has 50 bar left, that would be perfect as this is the lowest your cylinders should get to on a dive. As you are still wearing the weight to correctly sink your exposure suit, all you need to do now is increase your load in 1 kilo or 2 pound increments. You continue to do this until you now have enough weight to sink when you breath out with an empty BCD. You should find that with 50 bar left, you can descend to 3/5 metres and stay there with a nearly empty BCD. Now when you start a dive, you will be slightly heavier due to the weight of air in your cylinder, however you can compensate for this with your BCD.
This is the correct way to be, for the following reasons;
Swimming underwater is much easier and more efficient.
Ascents and descents are easier and slower as you’re using your lungs much more efficiently.
You save your back from carrying extra lead to and from the water.
Once weighted properly, if a problem was to occur such as your BCD failed, you will most likely be able to still use efficient up-wards kick to make a SAFE ascent to the surface. However, if you were heavily over weighted, you would struggle to maintain a steady and proficient kick which will then create a serious problem. I'm wearing the weight you say, but I still feel like I am too light at the end of a dive. Remember that your lungs act as a really big BCD and when you make an ascent, many divers feel they need more weight.
This is due to the diver ascending from, for example; 18 to 8 metres while breathing normally and continuously letting air out of their BCD, find their ascent easy. When they get from 8 to 5 metres with only 50 to 60 bar left and a stop at 5 metres, this is where most dives find it difficult to maintain their slow and steady pace, while still having some air in their BCD. A good tip is to first anticipate this then, watch your computer/depth gauge and flutter your breathing like you learned in the hovering skill, this avoids any unaware ascents. I suggest you get into the correct position, with your left shoulder up and your feet down and watch your BCD for expelling air as you press the deflate button.
Notice that the air will expand much quicker in shallow waters, so be patient and really concentrate on your breathing and a slow ascent from 10 to 5 metre safety stop. Once there, go even slower the last few metres to the surface. The reason most people have problems with their ascents is that they rush the last 10 metres. Most divers get used to the fact that swimming down deeper can be easier, for your buoyancy changes are not as dramatic as in a few metres of water. You can add an extra 2 kilos or 4 pounds if you find this happens to you and then continue to reduce this as you get more comfortable with your ascents.
Where should I put my weight (trim)..?
This is a major topic therefore I will most likely write another article specifically on this subject. However for this article, here are the basics.
Whilst diving you should;
Maintain a sky diver (horizontal) body position, with your legs bent at a 90 degrees angle.
Depending on the quantity of weights you need, put the majority of your weight around your waist. (If your BCD has trim pockets, place some in there).
When using a drysuit with buoyant fins, you may add up to 0.5 kilo or 1 pound weights around each ankle.
The most important way of reducing your air consumption is to make sure you’re properly weighted in all diving scenarios.
Follow this simple 4 step process, before each kick you make:
1. Your buoyancy in the water is neutral.
2. Trim (head to toe) is flat in the water.
3. Decide on propulsion technique (I use frog kick for 99% of my propulsion).
4. Then kick to move (this way you get maximum efficiency out of the effort you put in).
I hope by writing this article I have given you some insight into how much weight to use and why it’s very important that you dive with the correct amount of weight every time. Please let me know your thoughts on this article by dropping me an email. If you would like to see other articles, please email me your suggestions and I will make an effort to accommodate your request.