Weighting for cold water diving

Warm water divers with a thin or mid-weight wetsuit might throw on 4-16 pounds of weight, but here in the Pacific Northwest, it is common for cold water divers to carry 22-30 or pounds of lead (or more!). We need all that lead in order to be properly weighted to offset our floaty drysuits, thick undergarments, hoods, and dry gloves. 

Using that much weight has special considerations for how and where we choose to carry our weight - in order to dive safely and comfortably. Consider these questions before you build out a kit to go cold water diving.

Can you safely and easily lift your kit and carry it in and out of the water?

If you choose to put all your lead into your BCD that means the entire weight of your kit is in one piece. For example, a high-pressure steel 100 cubic foot (HP 100) tank tips the scales at around 47 pounds, if you have 30 pounds of lead you can easily be looking at over 80 pounds of weight just for your scuba unit - not including your drysuit, undergarments, fins, and mask. For many of us that is more than we can safely lift or move around as we don and doff our gear. Splitting up your weight into two or more systems, such as a BCD and weight belt or harness, can help to reduce that burden. 

Also consider whether you are fit enough to carry all this gear in one piece in and out of the water. If not, perhaps consider multiple pieces - which you could carry to and from the water in two or more trips.

Will your assembled kit float?

Many BCDs are designed with lift capacities that are more than adequate to float the BCD when weighted for tropical diving, but that may fail to float the BCD when wearing enough lead to dive with a drysuit (or double-layered 7 mm wetsuit). Let's walk through a specific example. 

• The lift capacity (upward buoyant force when fully inflated) of the popular Aqua Lung Pro HD jacket style BCD in a women's small is only 25 pounds. 

• A woman of that size wearing a drysuit might need 22 pounds (or more - it varies a lot based on body composition, experience, and choice of drysuit + undergarments + gloves + hood) of lead when properly weighted. 

• Let's also say she prefers a Faber-branded HP 80 (a high-pressure steel 80 cubic foot capacity tank). With a valve that is about 8 pounds negatively buoyant when filled with gas to its rated capacity of 3,442 PSI. 

• The weight pocket capacity of this BCD is 20 pounds (10 on each side) so she can load almost all of her weight into the pockets and then have plenty of room to throw the remaining two pounds into trim pockets on the cylinder band.  

This feels great! All your kit is in a single piece - everything is nice and tidy. But is loading all your weight into a BCD like this a good idea? 

• What happens if you need to remove your kit at the surface to fix an issue like a regulator hose that got trapped under a waist strap? 

• What happens if you need to remove this kit in an emergency - will it hinder you? Will you be able to recover it if it is at the bottom of the ocean?

• For small boat diving you may take yourself in and out of the boat separately from your gear. This makes it easier to get in and out without being weighed down. What happens when you drop your kit over the side of the boat to start your dive or take your kit off at the end of the dive?

• If you have a problem underwater and decide that the best way to deal with it is to partially remove your kit (unlikely but possible in situations like a severe entanglement that you cannot see because it is behind you on your tank/kit) - what happens when you remove your kit and it wants to sink and you want to float?

This kit will have over 30 pounds of negative buoyancy from the lead and the tank when assembled (plus a bit more for regulators, flashlights, etc.) - offset by only (at most) 25 pounds of lift. BCDs do not always achieve their full lift rating - for example if the bladder cannot inflate fully due to constrictions of its fit around you and the tank- then the actual lift it provides may be several pounds less than the nominal lift in the manufacturer's specifications.  

If you take this kit off in the water it will sink even when fully inflated! 

• (30 pounds of negative buoyancy) - (25 pounds of lift) = -5 pounds of net buoyant force

• It will sink aggressively if it is not inflated

How will you safely respond to a drysuit flood or BCD failure?

You can lose significicant buoyancy during a dive if your drysuit floods or your BCD fails. While severe drysuit flooding is not common, it can and does happen. So it is worth considering how you would handle a failed zipper, dry glove, neck seal, or tear that may lead to the loss of several pounds of buoyancy in your drysuit.

• Is the lift capacity of your BCD or wing adequate to compensate for this loss - even when your tank is at its heaviest? 

• Is removing some (but not all) of your weight (e.g. take some smaller weights out of your BCD pockets, off your belt, or out of your weight harness) to ensure you can become neutral and make a slow safe ascent an option?

What equipment might help you manage the risks and burden of diving with lots of weight?

Consider a weight belt or weight harness to supplement your weight integrated BCD pouches

• • Taking some weight off of your kit helps ensure that your kit can float at the surface on its own. 

  • This ensures that a significant portion of your weight is ditchable at the surface or even underwater in a controlled fashion in the event of a drysuit flood or BCD failure that results in a loss of buoyancy.

  • Wearing a belt or harness makes you less positively buoyant when separated from your kit (don't worry - you'll still float easily in a drysuit) - and your kit less negatively buoyant when separated from you. This makes it easier to hang on to your kit should you need to remove it underwater (you will be less floaty and it will be less sinky). 

  • Belts and harnesses give you more locations for placing weight toward your toes. This can help you fine-tune your weight distribution for proper horizontal trim - particularly if you tend toward floaty feet.

  • You can remove the weight belt as soon as you exit the water (or when you reach the boat) to decrease the strain on your back and decrease the risk of falls or twisted ankles on tricky beaches or boat ladders.

Consider a backplate and wing instead of a traditional jacket style BCD.

• • A steel backplate places 5-6 pounds of the weight you need to sink right next to your body - where it is ergonomically easier to carry and more optimal for trim (spread out pretty evenly from shoulders to lower back). This also reduces the amount of lead you need to carry in pouches, a belt, or in a harness - which reduces bulk and makes you a bit more streamlined.

  • Wings pair with backplates and are sold in various lift capacities for single and double tank diving.  It may be easier to buy an appropriate wing lift capacity for drysuit diving in cold water than it is to find a similar (beefy) lift capacity in a jacket style BCD that fits your frame. 

  • Ensure your wing lift capacity is more than enough to offset the maximum amount of weight you might carry on your kit (including the weight of the backplate and net weight of your tank in the water). Around 40 lbs of lift is somewhat typical for single-tank wings for cold-water drysuit diving. Discuss your options with your local dive shop. 

  • Backplates and wings are modular. You can modify your kit to dive doubles or clip on a pony bottle for spare air. You can easily and cheaply replace the harness webbing if it wears out. Most traditional BCDs are not as modular.

Use a steel tank. Consider an HP 80 if you are an average size (or smaller) woman or a shorter man. 

• • Almost all drysuit divers in cold water use steel cylinders. Steel tanks are denser than aluminum - so you don't have to carry as much lead when diving them for a comparable amount of air capacity.

  • Due to its buoyancy characteristics and the weight of the tank itself - using an HP 80 can reduce the total weight of your kit on dry land by more than 8 pounds compared to an aluminum tank or an HP 100. 

  • An HP80 stands several inches shorter than an Aluminum 80 or an HP 100. Better accomodating divers with moderate-to short torsos. If you find your tank is so long it hits your butt and legs (or head) an HP 80 may be more comfortable for you.

Consider sidemount diving - in which you wear two tanks, one slung on each side from a central harness. 

• • Sidemount divers wear a harness and BC in and out of the water but they typically don their tanks in the water - so they don't have to carry all their heavy gear at once on land.

  • I don't dive sidemount - but some divers choose it to avoid lugging the full weight of all their kit up and down the beach or in and out of the boat. Instead they can carry their kit piece by piece to the entry location.

  • This can be a good option for divers with bad backs or wobbly knees.

This is by no means an exhaustive list, but hopefully this gives you food for thought about how to set up your weights and other kit components for cold water diving. Always be sure you can establish enough buoyancy to become neutrally buoyant and slowly ascend to the surface - and that you can become buoyant at the surface once you get there. 

When in doubt consult with your local dive shop and/or seek additional training!

Appendix

coming soon... table of BCD weight pouch and lift capacity  / table of scuba tank buoyancy