Testing the 7MM Buoyancy Myth 

Love your channel. @20 yrs ago I was at 100 ft doing my navigation dive in a 2 piece 7mm off Monterey CA, I weighed 220 had 30lbs of weight. My bc had a leaking dump valve. I did a few pulls on the anchor line to start my accent with kicks did safely with a stop have never ditched weight. My instructors fixed the valve never suggested a dry suit , they did use dry n semi dry suits. Warmth in pacific being issue but honest about cost. I think I was weighted heavy by standards of the time. I guess I was lucky to have good instructors

Love these videos. Really enjoy the real world science experiments. When I first started, I was overweighted by over 10lbs.. Couldn't understand why I was so bad at air, adding and subtracting air from BC, etc. Was a workout! After lots of diving, I figured it out and got it down big time.

Brian thanks for your honesty while talking about sales. It’s good to hear that which I already knew, but great confirmation. So living in Michigan Ive done all my training in a 7 mm suit (except dry suit). I dive to 100’ every summer in the straits of Mackinaw in a 7mm or a 7/8mm semi-dry wetsuit. 12 lbs is exactly the weight I use and 14 is too much. I loved your experiment and physics doesn’t lie. It can be done, I do it often. Definitely, if you have to PULL yourself UP the line, your too heavy. Shame on anyone who claims otherwise. Thanks again. Keepm coming.

Great video! I actually encountered this myth just last Tuesday. I was diving with a group that I had never dived with before. They were all diving dry suits. I was diving a 7/5mm wetsuit. Someone presented this myth and said “we won’t be diving to 100 feet today”. I had never heard of this myth and because I was a lesser experienced diver than this person I didn’t debate it. I did a weight check with ten pounds and found it to be ok. I dove that weight and was fine but felt slightly under weighted. My next dive I added 2 pounds and it was perfect. We dove to only to 64 and 56 feet respectively but with the little amount I was using my bcd to compensate my buoyancy I knew I would be fine at deeper depths with a complete failure of a bcd. Anyway, I’m going to send my friend this video and have the discussion with him, because I agree with you.

I didn't even know this was a myth...this is so ridiculous, whoever says you shouldn't be diving deeper than 100 ft with a 7mm wetsuit made for Scuba diving is an ignorant. I took my 8mm Mares Flexa down to the sand at the RBJ in South Florida, 248 ft, and at no point I felt like a catastrophic wing failure would leave me no choice but to dump weight, I had 12 lbs on me and there is no chance I would've dropped weights if my wing (BCD) failed. Plus, how can your BCD fail? The inflator button stops working? Orally inflate! Somebody stabbed your BCD at depth? Depending on the location of the hole you can still ascend! You BCD got hit by a torpedo and blew up completely? Use your SMB under your arms to add lift if needed. There is very rarely a reason to drop weights in scuba diving, most problems can be solved if you stay calm and think of a solution. Bryan, are you ready for another collab? How about we go underwater somewhere (warm though) and once we are at depth you stab a hole on my wing, and see how we recover from that?

Great demo. I fully agree that proper weighting is important. Also it is nice feeling when you don't need to play with the inflator all the time. Some other cosequences are better trim and lower air consumption. Something worth to put some effort. Proper weighting is not only for wet suit divers. It is worth of effort for dry suit divers, too. And the reasons are mainly the same.

Wow… I’ve never heard of this myth before. In the UK it’s all drysuit diving, but when abroad I also use a 7mm wetsuit with the usual abroad Ali 80 (standard in the UK is a steel 12 or 15ltr) and never had a thought about it. Bob on with what you say about being weighted correctly. Over weighted causes way more problems than it solves so absolutely spend the time to get it right from the start. Thanks for an interesting vid 😎👍

Wonderfully done Bryan! I too struggle to understand why this agency continues to say this about 7mm suits. Of the 3 "dir" agencies they're the only one's I've heard say this. Thanks for doing this video. I'll shoot you an email if I think of other similar ideas you may like to test. Maybe I can make it over to Lake Hickory sometime for a dive.

I took the Buoyancy course with SSI and it was beneficial I also used it as one of the Pre-reqs for the Advanced Rating so it was worth it cost wise as well. One of the difficulties with weighting comes from changing up gear configurations. I don't dive as much as I like but I've spread 20-30 dives in a season between cold water thick wetsuit Salt water stuff, and warm salt water thin wetsuit stuff, Warm fresh water stuff, and cold fresh water stuff. steel tanks, aluminum tanks, and I just switched from a Jacket BCD to a BPW setup. So As much as I try keeping track of the different combinations in my logbook there is still a lot of trial and Error.

A great video and very informative. Would love to see your weight requirements with a Trilaminate Drysuit, thick undersuit like a Santi400 and a single steel 12Litre cylinder.

That was a great demo. Normally I am slightly overweight because I’m usually on the bottom searching and prefer it but you look roughly same size as myself. I’m 220 5’9. I will say I never usually change weights because I will go fresh to salt water on occasion so my weights are set. Except for ankle weights if I use my drysuit,I think I will reconsider and review my trim again. Thanks for the demo

Bryan, Great video. I loved a comment that you you said that the dive industry has a problem with over weighting students, which needs to stop!!!!!!. I teach my students proper weighting from the start. The rest of the video was great. I have also dispelled the 7mm myth.

I would be so dead if this myth were true! Good to see your videos again, the youtube algorithm is throwing me crap content and hiding my favourite channels.

Good to see it demonstrated! But 27F at the surface, 52F at the bottom; I'd still be wearing a drysuit! I did all my training up to AOW in wetsuits and I've never been so cold in my life! Now with a dry suit and dry gloves an hour or more in the 40s is no problem at all. But in warmer water, I agree; for that I use a 6mm semi-dry and when correctly weighted for the end of the dive I've never had trouble emptying the wing and swimming up from 100ft for practice.

Great video. Tank will become more buoyant as the pressure drops. It would be more difficult to stay at your safety stop.

Hi, been a fan of your videos for quite a while. very informative, professional and to the point. quick question out of curiosity. you were carrying 12lbs on this dive. How much do you estimate you would carry with the same gear in salt water??

Great video Bryan. Well done. 👍 Where does this type of complete BS come from? I used to dive a .25" (6.35mm), farmer john wetsuit (so my entire torso area was covered by .5" (12.7mm) of neoprene) in the great lakes while diving wrecks. I ran 80 cu.ft. tanks, and sometimes my double 80's. I wore 12-14 lbs. of lead and rarely used my BCD. I spent a whole bunch of time diving below 100' and never once had any issues with buoyancy. SMH... 😲😲Oh, good lord!!! I just listened to the Podcast these people put out. I listened to #10 first since it was on weighting. Not only are they spouting this complete BS on 7mm wetsuits at depth. Then they follow it up with putting your weight belt on and THEN putting on your back plate and wing over the top and hooking the crotch strap OVER the top of the weight belt, and then to look in to putting additional "ditchable " weight in pockets. Where do they find these people? And then I listen to #33 and these guys are spouting this garbage live to a group in Las Vegas... WOW. No wonder we have so many confused divers out there....

Single-layer 7mm is totally doable (nice demo, as usual!), as its surface buoyancy is about 15 lbs. At that depth, you probably lose about 8-10 lb from compression, and the non-reserve air left in the tank was probably about 4 lbs. That makes the swim up about 13 lbs negative buoyancy (which gets easier as you ascend). For completeness, you should have shown you can hold the safety stop at reserve tank pressure, which would hopefully satisfy those who doubt that 12 lbs of lead makes you properly weighted.

Great video and really great information! Thanks sir and keep up the good work!

This is the first time I’ve heard about that myth… fortunately, because I have dived many times with a 7 mm wetsuit… I don’t really understand why someone could use such tactics to sell a dry suit. I mean, a dry suit is easily sold once you have tried it. Once I owned one I got rid of my 7 mm right away…

7mm feels like 1 mm at 100 feet in the Great Lakes 🥶. Great video.. There may be a difference in the Farmer John style 7mm in its dual layer set up. There's a lot of neoprene compression and expansion going on...

Agree 100'%. I would just add that buoyancy depends on type of neoprene as well but difference is maybe not big enough to incalculate it. Greets.

Your clip will help a lot I hope, because I know how it felt to be overweight, when I did my deep dive, I had 12kg because I choosed 15l tank, which I knew was perfect to me, I did few more guided dives, I really wanted to go to 40m with my dive instructor, so from my experiance I did the math:12l =10kg, 15l=12kg, which means 18l=14kg. He kept me doing, because I guess he trusted me, we did the dive to 42m, everything was finde until we get back to the boat. He told me smiling: don't you think you were overweighted? I told him about my math, which made kind of sence to him, the captain, a kind girl heard us and she said: 15l or 18l aren't this much different, so when I did the secound dive with the 18l, I kept the 12kg. Which was perfect, to be honest I'm very thankful to my dive instructor keep me doing, it was just we both and it was a save dive, I'm the kind of person who love to risk, I don't mean if it would become Dangerous, but me it helpped a lot, to get this experiance, because no I know what weight I need if I would choose a 18l again. But which really wonders to me? Was my math so wrong, because 2kg more between 12l and 15l was always perfect. So I really wonder is there a kind of rule? :) To me he is one of the best instructor, because he just let me die, I guess He knews 12kg or 14kg isn't a big deal, where we dove we reached the bottom so I couldn't go deeper, I prefer those kind of instructor who just give s chance doing little mistakes by yourself, I'm thankful, because my fault was in a save place, I learned a lot, if I had still believed my math is perfect, I don't know what would happen if I would go to the blue whole with 18l and 14kg. My you think bit different, but I like those instructor who let the student do, as long as it's not totally dangerous, or let them and just stop them before they go into the water. Like: okay you think you would need 20kg, here you are now walk few steps, so are you still sure you need this much? 😁 Except dangerous mistakes, as long as you learn something, aren't real mistakes. I wonder what you think, I would love to know what you think about my math and what I think about risks.

What are your thoughts on double steal (usual double 12L here in Europe) tank and 7 mm wetsuit? An excellent video like always...

Hello from the UK. Great video thanks. I switch between a 7.5mm semi-dry suit in the warmer months, then add a "sorty" style 7.5mm wet suit over my core. The 7.5mm semi dry on its own requires 12Kg (26.5lbs) and with the core Shorty, I cant get down unless my weight is increased to 15Kg (33Lbs), In the really cold winter months, I use a scubapro dry suit, and need 16Kg (35lbs) to get neutrality buoyant. When I was in warmer climes, I was diving with 6Kg (13Lbs) with a 5mm wetsuit. Always thought I was over-weighted, however after trialling less weights with every suit, these weights are correct. I'm assuming the semi-dry suits are way more buoyant than wetsuits with the same thickness? Then again at a combined thickness of 15mm, it's not surprising! All tested in salt water. 👌

I have 48 logged dives, and I’ve really started to focus on buoyancy & trim the last 10 dives… I dive in SoCal in a 7mm with a 3mm vest/hood and typically a steel 100… I’m currently using 14# total (all in front, no trim weights) which seems to be about right at the end of my dives. I heard you say use your lungs for buoyancy control, not your BCD - could you expand on this more please? Does that indicate that when properly weighted our BCD should be a “set it & forget it” item and we don’t need to add/purge air throughout a dive? I am wondering if I am still a tad overweighted since I do play w my air throughout the dive - especially on my ascent when I have to purge quite a bit to not ascend too fast. I have very large lung capacity, and I can really notice my buoyancy change simply by breathing, but I also don’t want to spend an entire dive short breathing ( keeping lungs 1/2 full or 1/ 2 empty) as that takes too much concentration and I find myself enjoying the scenery less when I do this.

Great Video and Demonstration....up until 15.24 ;-)

Pretty interesting topic. I was also taught to overweight, and my buddies echo it as well. Good thing I've never actually had any scares yet, altho I am new.

I know you set out to disprove this particular case, but there are definitely cases where someone cannot swim up (even when properly weighted). Being tired/cramped is an obvious complication that could impact even the single-layer 7mm case you tested. More importantly, I'd say the real danger lies with double-layer / farmer-john suits, where folks have to fight 20 lbs (or more) of negative buoyancy to get off the bottom. (This is again, properly weighted: neutral at a safety stop at reserve tank pressure with empty wing.) Redundant buoyancy (whether that's a trusty buddy, a second bladder, or a DSMB or similar) is a good idea when 7+ mm wetsuits are involved.

Good video. Whats your opinion on 7mm based on that water temperature? Debating on 7mm or dry suit next year.

I dive in Cozumel in my 7mm semi dry (I get cold very easily) and I only needed 4lbs to compensate for al80 going 4ish lbs positive towards end of cylinder

thoughts on ditchable weights for ditching at the surface while helping another diver...? I enjoy non ditchable weight on my tank straps for trim nice and close to the backplate, but wonder about merit of ditchable weight for surface emergencies

Good stuff man!

I'm a new diver. I use a 5mm wetsuit. A steel 100. Halcyon blade and wing. Zero weights. My instructors don't believe in weighting to compensate for poor skills.

12:13 thanks for making me check my messages 😂 Most people around here only dove 7mm, and often with another layer, AL80's, no problems. Surprised this was a concern? But then again, that's what we learn in.

I learn more minutia from your videos, love it, thanks again.

I think people perhaps fail to understand the basic concept of "proper weighting" 1) Why do we need weight? Because with our kit on, we are less dense than water, so we float (ok, pretty obvious this one, but worth stating!) 2) What factors change our buoyancy with depth? Compression of our kit (reduced volume = reduced buoyancy) 3) What factors change our buoyancy with time? Exhation of our breathing gas during the dive (lower mass of gas = increased buoyancy) which leads too: 4) What is the correct weighing? The MINIMUM amount of additional fixed (ie attached to us somehow) ballast to ensure that we can accurately and safely control our depth at all stages of our dive. This is not a fixed or finite amount of course, and depends on the exact dive we are about to do. Clearly factors 2) and 3) work in opposing directions. We tend to start our dives with a full (heavy) cylinder and on the surface, ie at a shallow depth (least compression, most buoyancy) but we tend to end our dives back on the surface (most buoyancy) but with an empty (ish) cylinder. This makes the critical point for our dive mostly likely to be our final safety stop. As accurately stated in this vid, the BCD is their to compensate for 2) & 3) For open circuit scuba the use/loss of breathing gas is unavoidable, so we have to start the dive with enough ballast to account for the mass of air we plan to use, and hence use our BCD initally to compensate for that extra ballast. However, really, unless you are diving with large doubles, then the sort of masses of breathing air we are talking about are between 1.5 and 3 kg. This means that a BCD failure leaves us with a total negative buoyancy of just 3kg. This for anyone wearing fins and with the ability to breath in fully (your lungs are around 6 litres / 6kg or more and they are the most reliable BDC you have!) should, as demonstrated in this video, pose absolutely no issue what-so-ever in terms of being able to initiate an ascent. For anyone new or perhaps unsure, i'd recommend two simple tests, that can really be carried out on pretty much any dive: 1) On your final safety stop, just before you surface, get into the habbit of establishing an idea of just how much air is actually in your BCD. YOu can do this by actually letting it all out (you may be surprised by how much air is in there!) or by simply reaching behind you and feeling how full your BCD's bladder is. Do this on dives with different conditions and set-ups and you'll soon get a picture of your excess buoyancy at this critical part of the dive. 2) Establish what you can swim up against in terms of ballast: This really requires a pool or shallow site to do safely, and make sure your buddy knows what you are doing and is watching for any problems. Grab some spare weights start with around 2kg or so, in your hands, or in a mesh bag or similar. Descend to the bottom (3m is plenty deep enough), vent your bcd fully, and try and swim up. IME, anyone who is a competent swimmer, wearing fins, can actually swim up with a surprising amount of mass, especially if they use their lungs to act as the BCD (remember to exhale / breath as you start to ascend of course!). Once you've done it with fins, try it bare foot. What this does is give you confidence you can in fact cope without a bcd in most cases.

I am just wondering, why do we use bc??? According this very interesting test, the bc or wing in recreational diving is for comfort!

I was surprised you only had 12 lbs. Seems like when I dive my 7m semi-dry I need lots of weight. I'm 6', 215 lbs and took 36 lbs w/ a steel tank recently. I have no doubt I'm overweighted but I really struggle to get down if I don't. Does that seem absurdly high or do some people just take that much to get down? I'm assuming the former and there's something I need to be doing better. Thanks for the informative video!

How many different 7mm wet suits did you test? @UTD Scuba Diving @Ben Boss

Can you do a video about not touching marine life? And then watch it yourselves?

Wow that's cool . yesterday i was practicing on my byuancy in salt water wearing a 3mm full suit and i stuffed my bc with 21 lbs of lead and went down to 20 ft. I was able to surface without inflating my BC. I didn't even feel im too heavy. For freshwater i use 16lbs with a 3mmfull suit. Im 5'6 240lbs so i just figured out the perfect weight for me. Thanks for the great video 👍👍🦈

i think this idea stems from your wetsuit losing all buoyancy by the time you reach 100 ft, and if its a 7mm wetsuit that could be around 20-25 lbs depending on what size you are...so your bcd would need to be able to compensate by the same amount in order to maintain neutral buoyancy?

I realized I'm fine with 10-12 kg (12L or 15L tank) on salt water. And around 6-8kg for fresh water. I realized I'm maybe 2kg over weighted, but with 36 loged dives, I still use more air, so those 2kg are just something little a safety weight not to rise too fast, secoundly I guess 2kg isn't a big deal, I guess those 2kg more can be handled without ever need to be dropped. I would love to know what you think.

I have dove many times in Lake Michigan at 41 degrees water temp to 130 ft wearing a 7mm wetsuit. Buoyancy and trim are not a problems...cold is. On the first dive you feel warm enough, but the cold catches up with you on your second dive. We do it all the time here...until we can afford a dry suit. :-) Perhaps the noted myth is among those who live in warmer climates? You don't hear it in these northern parts.

What size wet suit you have ? Weight

My daughter got nailed for hitting the elevator button on her ow checkout, she was kicking her butt off and couldn't swim up the 20 plus pounds. She is just a scouch over 5 foot tall and thin with a 5 mill, I wasn't happy

My wife just got a new BCD and this warning is actually in the manual. It states that the Small and X-Small size may not have enough lift capacity if you have a wetsuit thicker than 6mm at 99ft/30m. That was the first time I have ever heard about this. Overly cautious company lawyers?

What size wetsuit? Weight ?

What about full to empty weight difference in the aluminum 80? Would you not have to add weight so at the end of dive you are perfectly weight and balanced. We lose 5 pounds on the tank

Lol my first checkout dive was in 32 degree water ..I where a 5 mm with a 3 mm under that's how I learned ..no issue it's absolutely correct what your saying ..

12 pounds is awesome brother 24-28 pounds was my goto when I started ice diving in a 7mm It's much less now in a dry suit but after this video I'm hitting the pool Godspeed

Don't know who made those comments.. I learned in a 7mm with an all80. Up here in Northern Canada most wet divers are in 7mm .

Why did you even take a buoyancy compensating device with you for this experiment? If I'm only diving 100ft and swimming up to shore I do not use one. In my opinion a b c d for recreational purposes is just a way to turn yourself into an SMB. Useful for waiting for that boat to turn around but not much else. Thank you for your videos, you are awesome.

What a joke of a myth, I’ve done this with a 9mm suit. Rolling my eyes.

I'm impressed by 12lb. I can dive 12 lb with a steel tank or an AL63 and a semidry but I'm better off with 14 if I run the tank down. A drysuit doesn't really become mandatory until you get to steel doubles. The margins for a neutral rig get pretty slim. Snow diving in a wetsuit, lol. You're silly.

That claim you debunk is also nonsense because you would orally inflate your bcd, if you need to, not ditch your weights, which should be emergency out of air procedure only. Even if BCD had a hole in it, and couldn’t inflate at all, you shouldn’t be so overweighted that you’d need to ditch your primary front weight pouches. You could have your buddy remove trim weights. But if I was a student in that shop I’d want to know why whoever is claiming this has me so overalls weighted that I need to buy a dry suit? Which ironically is much harder to control your buoyancy because it’s a whole other airspace you have to control. So if they’re not teaching proper buoyancy without a dry suit… not to mention you can play the same what if game with a dry suit. Okay, instead of my bcd I have a hole in my dry suit, by their logic it’s back to the same problem. So yeah, I totally don’t get the original point and am happy you debunked it.

Whoever believes this myth needs to come out to Channel Islands National Park to dive. Should also learn to properly weight themselves.

Unfortunately it shows how inexperienced you are to make a comment like this. Not on about how many dives you have but life experience. Divers are taught never to touch marine life, true. Why? Well when you take a child into a fine china shop you say "don't touch anything" not because they can't but because you are worried about them breaking something or hurting themselves. This is the same principle. You can touch marine life. If you know what you are doing. Should someone with no knowledge of that marine life touch? Hell no. Should someone with that knowledge touch? Yes asking as they are not causing any harm. Plenty of turtles, groupers, sharks and other marine life seek humans for interaction. And guess what if they don't want interaction they move away. Now if you chase that poor creature then again that is wrong. So as you see it's not as black and white as stating "don't touch" Btw great work Brian, really enjoy your videos. Look forward to them

Crap visibility

This video doesn’t prove anything and potentially leads people into dives where they are at increased risk due to an unbalanced rig. A typical ‘7mm’ Farmer John style wet suit/semi dry has way too much compression to be considered safe practice with steel tanks. I say this having learned to dive in one - diving steel tanks. I needed 14kg of lead to break the surface (salt water) and at 20m depth, my BCD used to be full of gas (blowing off) trying to hover without finning. The bcd I had at that time had 14kg of lift. At least the agencies that highlight this issue make their students aware of this, unlike many of the mainstream ones where you charge extra for buoyancy courses, that should be taught from day 1. Safe diving.

BS, you did not do a vertical ascent and you were resting and holding onto the wreck at the deepeest point when you would be heaviest. If it is a safe configuration then why did you not swim up vertically? and you don't understand physics or vectors or you would understand that kicking up a angled line IS using your fins to facilitate the ascent. In addition, you failed to demonstrate that your weight was sufficient to hold a safety stop with no air in the tank. The reality of the situation is that you were under weighted and you were not wearing a thick hood, nor a two piece 7 mm suit which wouldfd have more bouyancy. You fail on this demo, Although I give you credit for going to 100 ft in cold water in a wetsuit.

Today is 6/1/23, I also had heard the Myth, or Concern, or Warning, Thank you, for Taking the Time, to show me just how Important it is, to Spend the Time, to get Properly Weighted, Great Job. I'm right now Trying to find a 7 mm full suit to fit my Dad Bod, I saw quite a few comments with guys my size 5'9" 220 Looks like XLS with room for the One Pack Ab, Damn gravity is a Cruel Bitch. Aloha Ben

Whoever believes this myth needs to come out to Channel Islands National Park to dive. Should also learn to properly weight themselves.