BCD Lift - How Much Do I Need? - Scuba Tech Tips: S15E05
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- čas přidán 10. 05. 2023
- Some divers think "bigger" applies to all scuba gear including their BCD lift capacity. Alec explains why more BCD lift is not always a smart idea.
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For me, the defining case is at the surface: will the BC float me and my gear with my head a reasonable amount out of the water? I find the amount of lift I need is less than new divers might think. I'm a slim 150lb and my first Scubapro BC had 45lb of lift, pretty standard for a medium size. I replaced it with a 30lb wing and that was more than enough with a single cylinder and wearing just swimmers. I now have 40lb twinset and sidemount wings and they again are both more than enough to float a pair of steel 12 litres and a stage, and all the other gear we like to take along. So even with a lot more gear they are fine with less capacity than that first 'standard' BC. But there's another reason less is often better. The bigger the lift bladder the more the air can move around in it and this causes 2 problems. First, it may not always be near a dump valve and you don't wan't to be twisting and turning to get that bubble somewhere it can escape. The second concerns trim. If you have a big space for the air to move it will move as you go head up or head down, shifting your centre of buoyancy by up to a couple of feet. Your CofG doesn't move so that can make you quite unstable. This is one of the reasons sidemount wings can be so comfortable because the air is concentrated in one spot around your middle and can hardle move at all.
Thanks for the good information Tim. This was intended to inform divers not to believe bigger is always better with lifting forces. Trim and CoG are important especially if a quick dump is needed and the air bubble is not over the valve. Hope to do a follow up on lift calculations in a future video with the points you shared. Take care.
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A doughnut is a type of wing, and is used to differentiate it form a horseshoe style wing.
There is another negative from having too large of a wing, they taco around your tank, and it can be hard to raise the inflator above the highest point on the wing. Which is why you sometimes see a tank's physical size influence the size of your wing. Like a 60lb wing with a pair of 7" tanks often will taco too much. While a 40lb wing when wearing 8" doubles they might not have enough room to fully inflate.
Thanks.
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Thoroughly enjoyed this video! Great info & explanations.
Glad you enjoyed it!
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Hi Alec, i love your videos, I spent a year watching all the play lists but now I'm up to date so have to wait for each one. I'm now watching Alec at the Ranch as well 😊. I bought and i am reading Trailblazer after watching your interview with Dottie Frazer. What an incredible lady ! Thank you for the knowledge and the entertainment. Best wishes from the Uk. PS i am a wimp and only dive in nice warm waters 😊
Have you watched my Sea Hunt Remembered playlist? Lots of fun memories of Mike Nelson that got me started on scuba looooong ago. I like really warm water these days so I'm totally with you on that point. Take care.
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👍😎🇵🇭🤿! Thanks enjoyed watching another one!
You are very welcome.
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Thanks Alec as always!!!
You are welcome and thanks for watching.
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Great info. I chose a 60 lb wing only bc I run over 30 pounds of weight and sometimes find heavy objects while searching the bottom. Only use max inflate while floating back to the boat with a heavy payload. Always love you videos.
For other people reading this, lifting anything heavy enough to send you rocketing up if you drop it is what lift bags are for.
In general you are better off with a lift bag than trying to lift with your BC. What if what if whatever you are carrying slips? Now you are cosplaying a Trident missile on its way to start WW3.
@@Teampegleg you are exactly right, however, I didn’t provide any context. I fossil hunt, and sometimes we find upwards of an additional 30 to 40 pounds of fossil material. Usually secured in bags attached to the BCD. So the extra lift at the surface helps with that. Definitely not using the BCD to lift off the bottom.
Glad you clarified the lifting method for your fossils. Others were concerned too. Thanks for the feedback and hope you find big dinosaur bones.
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@@AlecPeirceScuba_SeaHunter I definitely should have read that comment before sending. Great community you have created here. Lots of great divers.
Very Well said Alec!
Thank you sir.
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Useful topic! 😃👌 Buoyancy in general is something we should pay attention to, all the more critical in waters that aren't tropical.
Totally agree. Hope this helps educate divers on proper (not just bigger) BCD's.
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Great video again Alec. A starting point to many discussions and lessons I hope around weighting and buoyancy.
I use a Backplate and wing but am not a tech diver. It feels more comfortable to wear and amazingly configurable. I think we should not categorize BPW with technical diving only and bring it into mainstream divers. More options are better for all of us.
I think you are right, more rec divers are going BPW simply for comfort, light and very configurable. This is intended to be one of several on BC lift. Next will be calculation of lift/buoyancy. Thanks for the feedback.
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Your videos are great, always packed with information, but still fun and concise.
I’m a cold water diver - Edmonton, Alberta. My current setup is semi-dry 7mm and a jacket bcd with 50+ lbs of lift; this requires 30 lbs of lead weight. I’m looking to switch to a bpw and hope to decrease the amount of weight, or at least distribute it more to the backplate.
Hello and that sounds like a good start. Check with your LDS before purchasing to get all your questions answered. Maybe consider side mounts to reduce lead and better balance?
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Great tech tip! I use a 60 lb wing, but never rely on the wing to dictate my ascent rate. Found it’s best to slowly ascend by finning up and then gradually adding air to achieve neutral buoyancy.
Going up slowly is so much easier and safer than those that rise at the fastest rate their dive computer will let them.
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Poor kevin will get PTSD from working for you😂😂😂😂
He gets great knowledge and forever poked by his friends.
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I think it's about time we meet the infamous "Kevin"! 😂
He says he has a face made for radio only....
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He's made an appearance before in Alec's bloopers video many years ago. These two are a funny duo. You should check it out😂😂😂
Hi Alec. My Shop sold me an Aqua Lung Omni in a custom size. It's a Medium with a Small Cummerbund. I'm 5' 5" weighing about 150 pounds. The Lift according to Aqua Lung is 36 Pounds. Believe it or not, During my OW Dives I used a 7mm 2 piece. 5mm Bots. 22# Lead. And I was still Positive Bouyuant to about 15 Ft down. I have not had a chance to Test out the BCD. Hoping next spring for the AOW Class.
In your case it's not the BC but how much of a cork you are and the lead to get down. It's always a surprise to cold water divers of any size how much more lead is needed to get below the surface. Look at my videos on weight distribution and trim for ideas to get horizontal, once you're going down. Compare this to a nice warm water dive and then the BC lift factor comes into play.
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one variable that should be taken in account is the weight of air you breathe and expel with the result that when you come back at the surface after you spent your full tank of air, you're in fact lighter of about 5 pounds so , if you started neutral at the surface, you finish positively buoyant, just enough to need a bit of correction, even if you spent your dive exactly at the same depth.
I , by far, prefer to keep all my gear as light as possible including my BC , it is a question of efficiency.
very good topic
very good video
Hi Jacques. Good additional tips for others to read about. Still more to come on BC lift calculations in a future video.
A.
Question: I'm 5'10 and 135 lbs. Would 27 lbs of lift be fine for me in cold water diving? (cold water meaning around 50 degrees F) great video thanks
That would be more than adequate. Of course, it will be balanced by proper weighting but I think you're on track. Alec
Hello Alec 👋
I have a question here for choosing the size of the BC and hope I could get any suggestion from you if possible.
I’m 108KG with high fat, I used to use 28lb BC with 2~4KG weights depends on what I bring with dive. And I lived in the tropical country, so only considered warm water recreational diving.
Basically everything goes well, even with the big wave at the surface, I can reasonable lifted my head out of the water without making much efforts. But some of my buddies recommend me to have a bigger one at least 38lb or bigger because of considering the rescue or heavy gears like full set of camera.
But I was curious do I really need that big size of bladder for example 38lb? Since now everything are all good, and I had more than 100 dives so not still a beginner anymore.
Any suggestion would be thankful, thank you Alec 🫡
Thanks for your comment.
BCD lift is a constant concern for divers even though it's really quite simple.
Assuming your are neutrally buoyant at the surface (as you ought to be), then you need only enough buoyancy to get your ascent started. Technically that is one pound!! That is, if you are neutral, only 1 pound of positive buoyancy will start an ascent.
However, the BCD is also used to provide a resting station at the surface and to do so it must offer support too.
Generally, a 25 to 35 pound BCD is more than sufficient for most divers. That is certainly enough to start an ascent. In fact, you will probably need to remove some air on that ascent or run the risk of an out-of-control ascent. A 25 pound BCD fully inflated underwater will pull you upward with a force of 25 pounds. That's a lot!! And that size will also provide a safe & comfortable support station on the surface.
The "Neutral At The Surface" premise applies regardless of your personal weight or any gear that you may be carrying. That is, your weight & body composition doesn't matter nor does the gear you have (double steel tanks, camera, weights, etc.). If you are neutral at the surface, that's all that matters. Carrying a 20 pound camera is of no concern - IF you are neutral at the surface - neutral including the camera!! The same one pound of positive buoyancy will start you on an ascent.
It has become a bit of a fad lately for divers to have BIG BCDs - "MY BC has 40 pounds of lift!!" implying that he is a good diver!
Complete BS.
Similarly I have listened to divers discussing their buoyancy & suggesting that they need 27 1/2 pounds, or some other magical number. They actually put a 1 pound weight on their belt to achieve what they consider 'perfect' buoyancy.
Again BS. Since the weight belt is part of your overall buoyancy concern, whether it is 11 pounds or 12 1/2 pounds is of no concern. Neutral at the surface is exactly that - regardless of your weight belt of other gear. A 1 pound weight belt difference really does nothing.
You have actually answered your own question. The BCD you have been using has provided you with sufficient buoyancy & surface support for your dives. I suggest you don't change what is working.
Alec
Note: I have not discussed the additional factors that can affect your buoyancy such as cold water exposure suits, extreme depths, etc. These should not apply to you in warm water recreational diving.
Thank you so much@@AlecPeirceScuba_SeaHunter!!
The answer and the the explanations are just awesome! Never expected I will get the response that detailed, so much appreciated.
I totally agree with you, actually I barely inflate my BCD but mostly using my breath to control the buoyancy, only if I felt hard to keep neutral buoyancy then will do some inflates. So I'm agree with you that a little pounds of lift would be enough for most situations I would have.
But I was asking more about how to distinguish if the lift enough when on surface, and sorry about that I haven't defined my question clearly. Because sometimes I will be a little sink when going down with the big wave, but not a big problem cuz just a little, I will float up soon. So I'm curious if bigger lift/bladder will provide me a better experience on the surface? Also if we're talking about the emergency situations e.q. rescue someone or my buddy, does 28lb enough? I'm not a coach, so actually I don't need to consider this as first priority, but I always dive with my wife, so I would like to do anything as possible to keep her from dangerous situations, that's why I raised the question.
But anyways, this is really a great experience and my honor that I can get the response from you Alec :)
i think my worst fear is bcd failure, then maybe i wouldnt get to the weightbelt, then kick off one of the fins in panick, sink and die lol. if im neutral at surface without air in bcd or suit i have some trouble getting down.. but probably i need some more traning.
Confidence comes from training and practice. If worried about a BC failure (very unlikely), in a pool or shallow water, with a buddy, practice a failure. Empty the BCD quickly by pulling the LPI hose, then dump 1 weight pocket to become positive. Don't need to drop both, one should be enough to become positive. Knowing you can recover will let you dive relaxed and enjoy it more.
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In that case you can inflate your SMB at depth and use like a pool noodle to help manage your bouancy. Just another reason to always carry one 😊
Did you see the video from the guy bought a big video camera et maybe other gear and die he when down to 300 metres could go up after a certain depth
Did not see that but very sad to hear. I know of a few divers with money and little brains do similar dangerous dives. This is just a tip to new divers not to think bigger is always better (except for dive knives of course).
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Are you talking about yuri lipski?
@@MorgueVOID yes 👍
Am I crazy? My goal is to almost never use air on my BCD. I should be neutrally buoyant, so at most a burst or two through an entire dive. I dont understand why youd nee such a big lift on a BCD unless you were retrieving stuff.
There are many factors to determine lift, key ones are body weight, BC, wetsuit, tank size. Kevin uses a XXL Avid, 100 cu/ft tank, 24 lbs, 3mm wet suit and is perfectly balanced for his situation (don't tell him I shared this). A surface check at the end of dive proves he's properly weighted. The Avid has 30 or 35 lbs lift so when he used to dive cold, add a 7mm full suit, hood, gloved, boots and his BC is just right amount of lift for cold diving. If you're 120 lbs wet, your situation is very different but in the end you're perfectly weighted and happy.
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@AlecPeirceScuba_SeaHunter thank you for your reply. Love your videos. My confusion comes from the fact that even with all that equipment wouldn't you still be neutrally buoyant? I understand a situation where the wetsuit is compressed but would that make a difference of tens of pounds in the negative direction?
Question, I’m shopping for my first dive computer. A radio controlled AI wrist computer is more than I want to spend now. So I was thinking of an AI computer on my high pressure hose. That way I can see all data at one time. However, my local dive shop said that is ok but recommended that I get a wrist computer for my right arm and have a analog air cage on my left side. Thus being able to watch my computer on my accent and hold BCD dump/air controls with left hand. What do you think. All the best. Jim from Georgia
Here is my view Jim. Your budget is the limiting factor in this situation. One thing long term divers learn is scuba gear is ALWAYS being replaced for one reason or another. Get the Air Integrated computer to do everything you need to dive safe and some day in the future it will be replaced (or complimented) by a transmitter computer. Kevin dives with an AI and wrist computer but stated with an AI only. Your LDS is thinking of the 'perfect' setup but you're not there yet. Probably have wetsuits, tanks, and other items to get too so don't sweat it. You can always hold the AI computer in your right hand, get a longer hose to help with that. Don't let others push you into a purchase you're not fully in agreement with. Another suggestion is to look for good used AI and wrist computer (from a reputable person/store) to get both at half price. Hope these tips help.
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Thank you for your help! I will go with the AI console unit. I do feel better about having all the data displayed in one location. Thanks again for your great videos! Jim from Georgia
Shout out to my boii Kevin 🤘
Kevin reads viewer and my comments so he likely is sending you a virtual high 5.
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You know your shit boy :-)
Thank you. Only took a few decades to learn it.
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The more things change the more things stay the same.
Change is constant.
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30 pounds is sufficient for 90% of tropical water recreational divers (excluding Kevin) 😂 😂 😂
OH you have not seen my dear friend Kevin up close. He does use an Avid BC which works fine for his slender form.
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@@AlecPeirceScuba_SeaHunter lmao his slender form😂😂😂😂
@@aliasincognito0 I would call this technical diving...even if done at recreational depths
I really enjoy your videos and often share them with friends. But this was probably your worst video. Yes, you discussed the issues of having too much or too little lift. But you didn’t discuss how to calculate how much lift you need.
He handed that to the LDS. I was surprised he didn't include the math, though.
Appreciate your comments and feedback. I try to keep focused on a few items in each video otherwise they are 30 minutes long and as we found out in the early days, viewer attention on CZcams fades quick after 5-7 minutes. A future video will cover lift / buoyancy calculation, tips and BC suggestions. Take care.
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