weight loss and buoyancy adjustment

[mintaka]

Motivated by diving, I decided to get in better shape and ended up loosing 10 lbs . I'm going diving next week and I'm not sure if I should put on less weight and if so how much ? Now I am 5'9" 150lbs with an average size frame.
Thanks!

 

[GrumpyOldGuy]

Not much difference due to body weight at all (ounces), most of your lead is used to counteract your wetsuit and other gear, not your body mass. But congrats on shedding 10lbs!

 

[ligersandtions]

Realistically, it probably won't change your buoyancy by much, if at all. But you should do a proper weight check anyways. I see that you're a new diver, and as such, you may be overweighted. There are many ways to do a weight check, but here's the way I prefer to do so:

At the end of your dive, get to a location where it's safe for you to touch the ground (sand is ideal) and are in 10-15 feet of water. Get as much air as you can out of your wing; have your buddy help make sure it's completely empty if possible. If you're diving dry, remove as much air as is comfortable. If the pressure in your tank is greater than ~500 psi, purge down to 500 psi. When you have all these requirements met, check your buoyancy. If you breathe in, do you raise slightly off the ground? If not, remove a pound or two and try again. When you get to the point where you are neutrally buoyant, you will be properly weighted.

Congrats on your new motivation to get in shape and lose weight! Even if that won't allow you to drop pounds off your weight belt, it will make schlepping your gear easier....you will find many benefits from being in shape, so let scuba continue to be a motivater!

 

[Teamcasa]

First off GOOD JOB on the weight loss!

Given that you are a new diver, a weight change of 10 pounds will not likely change your ballast requirement more than a pound or two. The reality is that most new divers carry to much lead already so sheding a pound or two should not be a big deal.

Ligers suggestion of a good weight and bouyancy check at the end of your first dive is a good one.

 

[mintaka]

Thanks for the replies ! I haven't had the opportunity to do the buoyancy you suggested ligersandtions, since all my dives, past and near future are boat dives out of Key Largo. I did however take the AOW peak buoyancy class and converged on 15lbs with a Catalina (compressed Al) tank. However the next day I dove with a different shop that had regular Al tanks (sorry dont know the volume) and was OK with 18lbs at first, but was too light at 700 psi at the end of the dive.
Next week though I'll be diving with the Catalina tank shop so probably 15lbs will be perfect.

 

[elan]

Thanks for the replies ! I haven't had the opportunity to do the buoyancy you suggested ligersandtions, since all my dives, past and near future are boat dives out of Key Largo. I did however take the AOW peak buoyancy class and converged on 15lbs with a Catalina (compressed Al) tank. However the next day I dove with a different shop that had regular Al tanks (sorry dont know the volume) and was OK with 18lbs at first, but was too light at 700 psi at the end of the dive.
Next week though I'll be diving with the Catalina tank shop so probably 15lbs will be perfect.

Assuming if you dive keys you do not wear 7 mil suit and assuming regular tank was Al80 18 lb is way to much with your body composition if you ask me

 

[PacificNWdiver]

A buoyancy check is important when you change gear. A 10 lbs weight gain or loss will not greatly impact your weight needs. Changing size of tanks and/or what the tanks are made of definitely will change your weight needs.

I would suggest asking the Dive Op what type of tanks you will be using and make notes in a dive log regarding the gear you use, and your weight needs for your future reference. On ascent I would also make sure your BCD does not have an air bubble that you are not aware of trapped in the bladder. Sometimes I'll do a shoulder "dip" or two to make sure any bubble is next to the release valve that I happen to be using at that time.

Good luck and safe diving.

God luck and good diving.

 

[Crowley]

it all depends on what you lost and what you gained.

Body fat is very buoyant so if you've lost 10lbs of fat then it won't mean a big change to your weighting requirements, but it will mean a change. On the other hand, if you've packed on a bit of muscle, this may have an extra effect, as dense muscle tissue is negatively buoyant. To some extent it will also depend on what size and shape you were beforehand - if you were 300lbs and now you're 290 - meh - not really gonna make a lot of difference - but if you were like 110 and now 100, much bigger percentage change.

As others have posted - do a weight check prior to your next dive. We're all different, and only you can properly determine what's correct for you and your gear.

Safe diving,

C.

 

[LouieLouie]

In metric terms: 1 liter of fat has a mass of 0,9kg. 1 liter of sea water has a mass of approximately 1,030kg. You will need approximately 0,130kg of weights per liter fat to compensate for the buoyancy of fat. Hence, for every kg (or lbs) of body fat you lose, you can reduce the amount of weights you carry by 0,130 / 0,9 = 0,144 kg (or lbs).

Since you lost 10 lbs of body fat, you should be able to dive in sea water using 1,44 lbs less weights than before.

 

[halocline]

I agree that it sounds like 18 lbs is quite a bit. It depends on the wetsuit you're wearing. Try tossing all the neoprene you're wearing and your BC in a mesh bag, in the pool or (even better) a calm spot in saltwater, and start adding lead to the bag until it sinks. If you have a 3 mil suit, which is pretty typical for the keys, it should be under 10 lbs to sink the bag. If it's more, take out the BC and try again. Some jacket BCs are surprisingly buoyant, which is yet another reason why I think they are the poster child for the dive gear industry gone wrong.

Anyhow, you can also put on a mask and snorkel, and check your own buoyancy in a bathing suit, you should be pretty close to neutral. Then add 4 lbs to sink the empty AL80, take away 2 lbs for your reg, add that to the weight to sink your wetsuit/BC, and that should be fairly close to your true weighting needs.

Then when all of this starts to get interesting and you still can't quite figure out why you're wearing so much lead to get down, try a steel backplate with a simple webbing harness (no padding!) and you can join the club of jacket BC haters.