change weights depending on dive plan

Been working to get the lead out and have just dropped to 20# from 28# a year or so ago. This weight was verified at 15fsw with about 500psi in my tank (steel hp 100). I was neutral and able to move up and down by breathing in or out. This has been great anywhere from say 20 fsw and deeper. Last couple weekends we have done a couple dives where we spend a good deal of time around 10 feet and I feel kinda floaty.
Do you guys adjust your weight based on your dive plan.
Thanks in advance.

I certainly would if I found the extra buoyancy when shallower than 15 feet to be a nuisance to deal with - especially if you are wearing a thick wetsuit. Diving is supposed to be fun - not a challenge to use the least amount of weight possible.

I usually adjust my weight according to the configuration I'm diving. The exception would be digging Quahogs, I try to be a few pounds heavy because I need the leverage to pry the Quahogs out of the bottom. I dive single tanks and ID,s in a wet suit or dry suit, light weight or heavy weight undergarments with three different size tanks. This gives me a lot of different weight combos. I keep them all listed on a laminated card in my dive bag. Examples: A ID configuration using 2 94LP tanks with a 7mm wetsuit require no lead. A ID config w/50LP tanks and the same suit requires 20lbs lead.

socaljohn:

Been working to get the lead out and have just dropped to 20# from 28# a year or so ago. This weight was verified at 15fsw with about 500psi in my tank (steel hp 100). I was neutral and able to move up and down by breathing in or out. This has been great anywhere from say 20 fsw and deeper. Last couple weekends we have done a couple dives where we spend a good deal of time around 10 feet and I feel kinda floaty.
Do you guys adjust your weight based on your dive plan.
Thanks in advance.

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Not based on the plan, but on the exposure protection.

You need enough lead to be able to stop at any point, not just 15'. Wetsuit buoyancy changes rapidly as you approach the surface, so being neutral 15' won't help if you need to stop at 5' to avoid a boat prop or just to look at something cool.

If you have a drysuit, this shouldn't be an issue, since you vent as you ascend.

flots.

If you find yourself having trouble controlling buoyancy during a shallow dive, it is likely that adding weight will make things worse, not better. In this case, I am talking about people finding themselves floating to the surface during the dive, dumping air to go down again, adding air, floating up again, etc. You see that a lot in shallow reef areas like Molasses Reef in Key Largo. I am not talking about having trouble staying down with a nearly empty tank after doing fine before that while the tank was more full.

When you are diving, you achieve neutral buoyancy through a balance of whatever is pulling you down and whatever is pulling you up. You are able to vary your buoyancy during a dive by changing the amount of air in the BCD and by inhaling and exhaling. If you have roughly the right amount of air in the BCD for your depth, you can control your buoyancy easily simply by the way you breathe. If you ascend enough and the air in your BCD expands to the point that you can no longer control your depth with you lungs, you have to dump some air. If you descend enough for the air in the BCD to contract too much for your lungs to control it, you must add air to it.

The deeper you go, the easier this is. That is because the amount of change in volume of the BCD by ascending or descending a few feet becomes less and less. Because that change is so pronounced in shallow water, it becomes most difficult to overcome those changes at those depths.

The less air in the BCD, the easier it is to control. A properly weighted diver will have very little air in the BCD. For every unnecessary pound of lead you wear, you have to add about a pint of air to the BCD to achieve neutral buoyancy. Every unnecessary pound thus adds more air that will be expanding and contracting with every little change in depth. Lots of people dive a few pounds heavy, meaning they might have an additional quart or so of air to contend with. That's not too bad. Add much more than that and you will soon find yourself at the mercy of a constantly expanding and contracting air balloon in your BCD.

When I am instructing in the deep end of a pool (about 12 feet), I am a few pounds overweighted intentionally, as most instructors are. I do a demonstration in which I go from the very bottom of the pool to the top and then back down again using nothing but the air in my lungs to control the depth. No problem. On the other hand, when I am practicing for technical diving in the pool and have big double steel tanks (etc.), I am significantly overweighted. I can only control my depth with my lungs over a range of a few feet because I have to have so much air in the wing that it has become beyond my control.

Verify your weight again @ 500#, 15', empty BC because you may need to adjust it again. I check mine whenever I can because I go between different tanks and rigs. At that point I add a couple of pounds in case I need to hold a stop with less than 500# or less than 15'.

Since you are diving at 10 feet you are not weighted properly for the end of the dive. You can make up for some of this by using your lung volume, however a few more pounds on the belt would make it easier. Next time weight for 10' instead of 15', and if you run your tank lower than 500# adjust for that also. If you are diving a wet suit, a weight check after diving deep will give a different weight than a shallow dive because of the crush and rebound of the neoprene, you will get a lower weight after diving deep.

I look at a weight check as an ideal figure and adjust the weight for my dive. I use a pocket XS scuba belt and weights down to 1# so I can change easily for the equipment and dive.

Oh yeah, if you have more than one rig or tank, take good notes on weight and you will avoid a lot of grief.


Good luck

Bob
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"If you don't like it, go on the internet and complain." Brian Griffin

AfterDark:

I usually adjust my weight according to the configuration I'm diving.

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Exactly!
I think for recreation dives weights should be adjusted according to equipment, not dive plan.

In simple word: If you change something in your equipment, which has not neutral buoyancy in all deeps, you should adjust weight. But your weights should not be changed regardless if you plan to go to 100ft for 20 minutes only or 100ft for 7 minutes and 30ft for next 30 minutes or 25ft for 1 hour.
One of possible weight checks (much more others were described here in other topics) : Stay on 10ft with 500 - 600 psi in your tank and completely empty dry suite (if you have) and BDC (or wing) and give to your buddy some weights from your pockets till you will be able to keep yourself without any body moving (hands or fins). When you find the needed weight, go to surf and try to go back to 10ft deep mostly without helping by hands and fins (or very light help), only long breath out. If you will be able to do both things above, this is the weight that you need. I usually add 2-3lb. to this weight just because in emergency situation you not always can release all air (especially from dry suite) like on training and your body weight also may change from day to day.

I may add a pound or two if I am diving in extremely cold water, and want to make sure I can keep my suit inflated enough to maximally loft my undergarment, all the way to the end of the dive. Otherwise, I don't change my weighting for different dives, although, of course, one has to adjust for fresh versus salt (and surprisingly enough, for different salinity as well).

Bob DBF:

Verify your weight again @ 500#, 15', empty BC because you may need to adjust it again. I check mine whenever I can because I go between different tanks and rigs. At that point I add a couple of pounds in case I need to hold a stop with less than 500# or less than 15'.

Since you are diving at 10 feet you are not weighted properly for the end of the dive. You can make up for some of this by using your lung volume, however a few more pounds on the belt would make it easier. Next time weight for 10' instead of 15', and if you run your tank lower than 500# adjust for that also. If you are diving a wet suit, a weight check after diving deep will give a different weight than a shallow dive because of the crush and rebound of the neoprene, you will get a lower weight after diving deep.

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Archimedes' Principle says that a body is neutrally buoyant, it weighs the same as the volume of water it displaces. It does not mention depth. The weight of water does not change with depth, so the volume of air you need in a BCD to balance that weight does not change with depth. Depth becomes a factor because of compression of air in the BCD and the wet suit. Lets lay you need a volume of 2 liters of air in the BCD to be neutral at your current weight--which only changes with the weight of the air in the tank. If you need 2 liters of air to be neutrally buoyant, then you need 2 liters of air to be neutrally buoyant, whether you are at 300 feet or at 10 feet. The difference is that because of compression under pressure, you need to add a heck of a lot more molecules of air to the BCD at 300 feet to get that same volume of 2 liters. If you add 2 pounds, then you will need nearly another liter of air to stay neutral. That is all you will have accomplished.

What does change with depth is the buoyancy of a wet suit. A wet suit will be more buoyant at 10 feet than at 15 feet. If you are diving with a 7 mm suit, you will notice the difference, and you may need to add more weight for that depth. If you are diving with a 3 mm suit, you won't notice it all that much.

Certainly in the early days before I started using a BCD (essentially the first 28 years I dove), proper weighting was far more critical to a successful dive. Today with a BCD I purposefully overweight myself so I'm more stable when filming on the bottom. I think the only dives I've ever done that were shallower than 10 ft were a few summers ago when I was filming a baby whitetail damsel that entered California waters. Sometimes my average depth was a mere 4-5 ft... but the tank lasted forever!