How Much weight???

[tyesai]

That PADI chart also had me overweighted a 100% as well. I guess it ensures you sink though.

 

[TSandM]

Weighting and buoyancy are really simple physics. If you think about it, your body is close to neutral. Some people are sinkers and other are floaters, but generally not enormously in either direction (in other words, a pound or two off neutral). An Al80 tank is 4 lbs positive when empty, so it takes 4 lbs to make that tank neutral. BCs vary more -- some are as much as 3 lbs positive (the jackets with a lot of padding) and some are 5 or more pounds negative (backplate systems with stainless steel plates). If you add all this up (and remember, you eventually have to include the buoyancy of EVERYTHING you take into the water -- fins, booties, gloves, hoods, lights, etc. -- you will come up with a number which is a reasonable estimate of how much your final weight will be, when you have got it tuned.

In your case, if you assume the 1 mil suit is no more than a pound positive (I think that's a fair assumption), your tank is +4, your BC is +2 (sort of an average for non-backplate systems), and your body is neutral, you'd be looking at something in the neighborhood of 7 pounds for final weighting. It could be a couple of pounds either way (obviously lots of fudging in my numbers) but you shouldn't be expecting to get down to no weight at all with an aluminum tank and a soft BC.

 

[NickPhillips]

i weight 170. I wear 10 lbs with a 3 mil and 6 lbs without anything.. I could go less but I feel comfortable with this.

 

[LanceRiley]

Weighting and buoyancy are really simple physics. If you think about it, your body is close to neutral. Some people are sinkers and other are floaters, but generally not enormously in either direction (in other words, a pound or two off neutral). An Al80 tank is 4 lbs positive when empty, so it takes 4 lbs to make that tank neutral. BCs vary more -- some are as much as 3 lbs positive (the jackets with a lot of padding) and some are 5 or more pounds negative (backplate systems with stainless steel plates). If you add all this up (and remember, you eventually have to include the buoyancy of EVERYTHING you take into the water -- fins, booties, gloves, hoods, lights, etc. -- you will come up with a number which is a reasonable estimate of how much your final weight will be, when you have got it tuned.

In your case, if you assume the 1 mil suit is no more than a pound positive (I think that's a fair assumption), your tank is +4, your BC is +2 (sort of an average for non-backplate systems), and your body is neutral, you'd be looking at something in the neighborhood of 7 pounds for final weighting. It could be a couple of pounds either way (obviously lots of fudging in my numbers) but you shouldn't be expecting to get down to no weight at all with an aluminum tank and a soft BC.

well... i was computing that I would be neutral at 8 pounds... im just getting there half a pound at a time since I make my own custom weights...

but like I said. i have this divemaster friend who dives with us. let me see... he uses Al80 tank, Scuba pro classic BC, Jetfins and wears a rash guard and shorts... and he doesn't wear weights!!! how does he do this if Al80 is +4 buoyant ???

 

[CamG]

Greetings Lance as TSandM has shared it is a matter of physics.
With a skin and shorts and a fresh AL 80 @ 3000psi depending on the BC I can dive that rig in the pool or safely to about 1750psi.
It is a bit of breathing control and as a DM you are always swapping, fixing, adapting rigs to get the students in the water safe.
DM's learn to deal with a variety of things and thus can dive just about any rig, OR SHOULD BE ABLE TO!

They do make neutral AL tanks or did but I have seen only a few here in IN.
The key to proper weighting is to do frequent weight checks at the surface.
In a little amount of time you will learn your rig and know what to use with your exposure protection even if you change it.
The key is to dive often and keep a good log book with details that way it acts as a reference for future use.

CamG Keep Diving....Keep Training....Keep Learning!

 

[DevonDiver]

thanks Devon Diver =)

a follow up question... what if due to work or time constraints.... i coudn't dive for say .. 1 month. do I have to increase weights? I've heard somebody say that the more you dive the more you become less buoyant... and the more you don't dive you become more buoyant or something like that.

Unless you went on a Pizza Hut and Xbox bender...and massively changed your body mass, then there's no physical variation.

However, a lay-off from diving can cause a psychological change - namely, you'll be less relaxed and that can impact on your breathing. This can have an impact on your buoyancy. However, it's better addressed by relaxation techniques than by the 'quick-fix' of slinging more weights on (because that won't make your dive easier or help you relax).

For more details of how breathing effects your buoyancy, read: Scuba Buoyancy Masterclass 5of9 - Trim and Position -Scuba Tech Philippines

 

[Interceptor121]

It is always hard for a holiday diver to establish exactly how much weight to have.
If you are relatively inexperienced it is better to start with a buoyancy check at the beginning of your trip (at the end of the dive not just at the start) and see how you get on and check if you can drop anything
You can improve during the course of say 4 days of diving however if the next time you go diving is in 6 months there is a chance that what you dropped goes back in and then you work your way through
This assuming there is no major change of your weight and body mass
In essence unless you are in the water almost every day you need to keep working on it but I would not be too stressed at dropping the last ounce of weight at the end of the day weights usually go at least in two pounds increments. Just for safety I prefer to round up and not down so that if the conditions are not perfect I am sure I can stay down if for example I end a dive with 30 bars.
So my advice is to keep working on it without being obsessed

The PADI guidelines, as stated in the PPB manual, are an INDICATION of how much weight to start they are not a set of equations to be applied to determine exact results

 

[D_B]

I have this formula saved from a similar thread ....

The following formula will put the needed eight in the ball park:

Body weight X .05
+ 4lbs. for an AL 80 tank
+ 1 lb. of weight for every mm of thermal protection

I got this formula for weighting from my open water instructor many years ago.
A couple of caveats:
The thermal calculation is a pound for every millimeter generally worn on the torso;
For fresh water use .04 in place of .05.

Again this formula puts one in the ballpark for proper weighting. But it's a starting point. Obviously experience, add-on gear, conditions, body composition, etc all play a part in proper weighting. I use this with students primarily to show them a target weight.
Dr Neil

This formula workes out very close for my actual weight needed in salt water (changing the +4lbs for a Al80 tank to -6lbs with a steel HP100 tank) and 7mm suit, hood, 3mm gloves, 3mm boots

 

[DivemasterDennis]

What an excellent thread- to which I will add this- note the weight you use on every dive in your log book, along with location, conditions, water tmp and exposure gear and tank size and type. Your might also note your weight. I am one of those people who puts weight on and takes it off from time to time, and that is a big variable. I also dive cold water in a 7 mil, fresh water in 3 to 7 mil, salt water warm skin or 3 mil, and so on and so on. I have over the years made my own "chart", and wear anywhere from 6 lbs to 16 pound depending on conditions, including the condition of my own girth. No rule of thumb applies- do a proper weight check , at least at the first dive of the trip/day/week. I always find that I am dropping a little weight between the first and second day's diving.
DivemasterDennis scubasnobs.com

 

[Bubbletrubble]

but like I said. i have this divemaster friend who dives with us. let me see... he uses Al80 tank, Scuba pro classic BC, Jetfins and wears a rash guard and shorts... and he doesn't wear weights!!! how does he do this if Al80 is +4 buoyant ???

@LanceRiley: "Compare and despair." -- Stuart Smalley (Al Franken's character on Saturday Night Live)

But seriously, Scubapro Jetfins, particularly with spring straps, are quite negatively buoyant. Your DM friend may also have an inherent buoyancy that's slightly negative. A reg setup can have a buoyancy of -2 lbs. Even with an AL80 tank (+4 lbs. when empty), it's not surprising that, with no wetsuit, your friend can be properly weighted without any lead at all.

You're good enough. You're smart enough. And doggone it, people will like you no matter how much lead weight you require.
(Just make sure you're properly weighted.)