Ladies and gentlemen, what’s going on – welcome to Scuba Diver magazine. My name is James, and I am Scuba Diver magazine’s ‘man in Miami’.
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This week is the next video in our series that we like to call Dive like a Pro and we’re focusing on Weighting. Later in this video, I’m going to be giving you my one single piece of advice for getting your weighting absolutely perfect like a professional diver, but first I’m going to answer the five questions that I get most commonly asked as a dive instructor concerning the amount of weight you need to go scuba diving, starting with why is proper weighting so important for successful diving.
Being correctly weighted is absolutely essential because having the right amount of weight on you ties into your ability to perform the four core skills of scuba diving that we’ve been talking through throughout this series of Dive like a Pro. If you’re over-weighted, you’re going to need to put more gas through your BCD, which is going to increase your gas consumption, which is going to mean that your buoyancy will be off and you’ll constantly be fighting an up/down kind of battle. If you have the weight incorrectly dispersed around your body, your trim will be off. If you have too much weight, you are going to have to kick harder than you should have to, which is going to mean your finning will be off-balance. If you don’t have enough weight, you’re going to be constantly fighting to get down. If you’re over-weighted, you’re going to be working harder, which means your breathing rate will be sky-high. There are hundreds of reasons why your weighting needs to be spot-on, it’s an essential skill of scuba diving, and as I said before it ties to the pillars of your scuba diving ability.
The next question I get – ‘dive gear is heavy, why do I need any weight at all, won’t I sink with just dive gear on’. No, you won’t. In about 250 BC, the Greek mathematician Archimedes lay down the law for what is basically an essential principle for all scuba divers and that is an object wholly or partially submerged in a liquid is buoyed up by a force equal to the weight of that liquid displaced, so even though, yes, scuba diving gear is heavy, it’s also bulky and what we’re focused on is not weight, but density, so if you have big bulky gear, as heavy as it is, it’s still going to displace a lot of water and that needs to be compensated against using something that is incredibly dense in terms of a lead block. I hope none of you who have ever thought about getting in the water without weight, but if you did you’ll notice it was very hard to go scuba diving even in bulky heavy dive gear. A normal human being cannot get themselves under the water without the assistance of lead. Scuba diving without lead is just expensive snorkelling, so we add enough weight to get us under the water and then add gas to our BCD to make sure that we’re not knuckle-dragging across the seabed.
The next question I get asked all the time as a dive professional is how much weight do I need. Well, unfortunately, there’s no easy answer or equation for this. I can’t take your body weight and add the weight of your gear and divide by the first number you think of, them come up with the right amount because a lot of it has to do with the composition of your body type. Add to that the different densities of the gear choices that we make and it’s not really a cut and dry answer. Still the best way to figure out how much weight a diver needs is trial and error. It’s to get in and do a weight check – more on weight checks a little bit later on – and refine it until you get the minimum amount of weight that you actually need.
Personal buoyancy plays a big part in how much weight you need to go scuba diving. In order to understand personal buoyancy, you need to realise that the different tissues that comprise the human body have different densities and therefore different buoyancy attributes. Bone is incredibly dense, but as you get older it’s less dense. Muscle is incredibly dense – think about two glasses of water, you put a lump of butter into one and a lump of steak into the other, the steak sinks and the butter floats. Your personal body composition is one thing, and then in addition to your personal buoyancy you need to consider your equipment when trying to figure out how much weighting you use.
While all new equipment choices have some effect on your buoyancy underwater, there are really three pieces of kit that change your buoyancy as the dive progresses – the first obviously is your BCD, which you need in order to make adjustments based on your other gear, so I’m not going to focus on that too much, but think about the other two, starting with your tank. First off, all tanks whether they’re steel or aluminium become more buoyant as the dive progresses because you’re consuming gas from them. Yes, gas does have a significant weight value and as you consume the gas, the tank gets lighter, which means it gets less dense, which means it becomes more positively buoyant. Now if you have a steel tank it is unlikely that even though it will become more positively buoyant, it won’t tip over to the point of being actually buoyant.
That’s not true of aluminium tanks – if you take a standard 80 cubic feet, as you consume that tank and you get it down to around just shy of 100 bar, that’s the tipping point where they go from being negatively buoyant to start becoming positively buoyant and then as you drain the tank further and further down, the more floaty the tank becomes, so you need to take that into account to make sure you’ve got enough lead for the end of the dive – more on that later. A third piece of equipment you need to consider is your thermal protection.
There is a huge difference between diving in a rash guard and shorts and a drysuit and the reason for that difference is displacement. A drysuit is a lot bulkier and it takes up more volume and displaces more water, which means you need to add more lead to overcome that buoyant factor. Even a couple of millimetres difference in the thickness of wetsuits when spread over the area of your whole body is going to make a huge difference to the amount of water that you displace, but not only that but wetsuit material changes its buoyancy characteristics throughout the dive.
At the start of your dive on the surface, the wetsuit is maximum thickness – as you descend and ambient pressure increases, the neoprene that your wetsuit is made out of actually compresses, which means as you get deeper your wetsuit becomes less buoyant. Then on ascent the reverse happens – the pressure releases, the wetsuit expands and you become more buoyant, which means your rate of ascent if not controlled properly will accelerate.
The third factor to consider after personal buoyancy and your equipment choices is the water type – salt or fresh-water. If you’re going from freshwater to saltwater you will need to add lead because salt-water is more-dense, and vice-versa going the other way.
How to conduct a weight check
Well, he we go in five simple steps:
Step one – Get kitted up, guess the amount of weight you need, make a giant stride entry into the water – having completed a buddy check first, of course – and then once on the surface breathe in a medium deep breath and hold it.
Step two – Raise your inflator over your head, tuck your other arm in and cross your ankles. The reason you do those two things is to resist the temptation to scull or kick – you want to be perfectly stationary.
Step three – Release all the air from your BCD and you should float at eye level still holding that breath. If your BCD is empty and your chin is still out of the water, you don’t have enough lead. If your BCD is empty, you’re still holding that normal breath and you’re sinking past eye level, you have too much weight.
Step four – Breathe out, you should start to sink. Don’t kick, just let yourself go down. If you don’t find yourself sinking you don’t have enough weight.
Step five – you may want to add an additional two pounds if you’re using an aluminium tank because obviously your tank is full at the beginning of the dive and at the end of the dive it won’t be full and you’re going to have to fight that positive characteristic of that type of cylinder. If you’re diving steel, don’t worry about it just go enjoy your dive and have fun – job done.
Why do some divers struggle with their weighting?
It’s true, I see this all the time on dive boats. I’ll be minding my own business kitting up and the Divemaster will be going around the boat and asking how much weight people need and I’ll see somebody who’s much smaller than me and is diving in just shorts and a rash guard with nice small gear and they’ll ask for like 10kg of lead. It’s a common mistake to think you need more lead than you do, and as I said, that’s just a really inefficient way to dive.
Although this series is called Dive like a Pro, it could possibly be a professional divers’ fault that you think you need more weight than you do because some less-reputable dive instructors out there, instead of taking the time to get their students right with their weighting as they’re going through the Open Water course, just sandbag them with as much weight as possible because, well, it’s kind of like walking a dog on a short leash really. If you have the dog under control you know where they’re going to be, and it’s the same thing with divers underwater – if you take your eye off a diver for a short while, it’s normally better than on a shallow training dive that your diver is in the sand at the bottom 30 feet down rather than shooting to the surface and bobbing around in boat traffic.
It’s not right, I don’t do it, I don’t support it, but that doesn’t mean it doesn’t happen. If you’re a diving instructor did that to you and convinced you that you need more weight than you actually do, I suggest you go back to them and ask for your money back or make them teach you properly. Ultimately though, once you’re certified, it’s down to you to refine the amount of weight you need and get it down to the absolute minimum that you can actually dive with safely and under control.
Now is the time for me to give you my one single biggest piece of advice to help you get your weighting correct and that is, do a confirmation weight check at the end of your dive. Think about the end of your dive – your tank is the lightest, your wetsuit, if you’re using one is going to be at its thickest and you’re going be the lightest you’re going to be at any point during that dive, so it’s actually more important you’re correctly weighted when you are trying to hold that 5m safety stop and get your buoyancy really on point. If your weighting is correct, you want to make sure that at the end of the dive you’re not shooting up to the surface and you’re correctly weighted for your safety stop, so a confirmation weight check at the end of a dive is a very useful way of doing that. Here’s how you do one in four easy steps:
Step one – Ascend to your safety stop and hold a tight hover.
Step two – Hold your safety stop depth and breathe your tank down, keeping a really close eye on your gas to just above your reserve pressure. I’d recommend doing this after you’ve completed your safety stop so you can surface immediately afterwards.
Step three – Offload portions of the weight that you’re carrying. I personally recommend giving small increments away. If you can get those little lead pellet bags that come in half-kilo amounts, that can really help you refine the exact amount of weight you need to go diving. If you’re not doing your safety stop on a nice sandy ledge where it’s easy to put small amounts of weight down and then retrieve later, I recommend just putting them in your buddy’s BCD pocket when they’re not watching once you’ve offloaded as much weight as you can without floating up. That is the minimum weight you need to complete the dive.
Step four – You’re still be able to breathe naturally and hold neutral buoyancy with that amount of weight. Once you’ve retrieved a little weight and you’ve made a safe surface and exited the water, you can make a note of how much weight you were able to dump and still stay neutrally buoyant. You now know what the exact amount of weight is you need for subsequent dives.