Charlie99
Contributor
- Messages
- 7,966
- Reaction score
- 166
- # of dives
- 500 - 999
Interesting that you don't have to add any weight when diving double AL80s.
Standard tanks or the ones with extra weight to make them neutral when empty?
Weight used with single AL80 and 3mm wetsuit
- Thread starter JohnCollins
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
Standard tanks or the ones with extra weight to make them neutral when empty?
maccajim
Registered
height 5"9 weight 62kg use 3kg weight or around 6-7lbs USA style,
SeaJay
Contributor
I dive with six pounds of weight in salt water... None in fresh.
...But that's not the whole picture. Here's the detail:
I'm 6'1" and 220 lbs. Body fat, which is something that completely makes a difference (muscle is negatively buoyant, while fat is positive) is around 17%. That's on the low to mid average for your regular American male, I believe. If I maintained a lower body fat percentage, I'd need less weight. More body fat, and I'd need more. Therefore, your mileage may vary. For reference, in a pool with no gear on, my body is either negative or positive depending on how much air I have in my lungs.
A 3mm wetsuit can very in buoyancy from manufacturer to manufacturer. In salt water, I am about 8 pounds buoyant with my O'Neill in only a mask, fins, and snorkel... At the surface. Go deep, and that number falls.
I dive a backplate and wing setup, with my backplate made of stainless steel. It's six pounds negatively bouyant... With little difference between salt and fresh water.
I also dive with a 1-pound "lightweight" STA.
I exclusively dive with Luxfer AL80 tanks, rated at about -2 pounds negative in salt water with 3000 psi (77.7 cu ft) and about 4 pounds positive empty.
Again, with this rig, I'm perfectly balanced in salt water with six pounds on my hips, and no additional weight whatsoever in freshwater. By the way, I have enough "play" in there to don a 3 mil hood if I choose... So I could lose maybe one pound without a hood, if I really wanted to.
So... The bottom line is, in salt water, with a 3 mil and a "standard" AL tank, if you include my plate and STA, I'm balanced at 13 pounds. I could probably do 12 without a hood. In freshwater, I'd wear only my bp and STA, for a total of 7 pounds.
Keep in mind that there are many AL tanks out there with different buoyancy characteristics... Luxfer also makes a "compact" AL80 and a "neutral" AL80 which are designed to be more neutral when empty and much heavier when full. If I were using one of these, I'd need less weight - but I don't use them because I've found that it messes up my trim (puts my center of gravity too far back).
For more information about certain tanks and their bouyancy characteristics, see http://www.diverlink.com/gear/tankspecifications.htm
Also, someone already posted this... And I'll "second" it... The best way to find the "correct" amount of weight is to follow the guidelines in the PADI OW manual... Take your "normal" equipment, and use a near-empty (less than 500 psi) tank into the water. With a full breath of air and NO air in your BC, the waterline should cut cleanly across the centerline of your mask... While you're floating vertically and looking straight ahead.
Of course, that's a great way to figure out your buoyancy AFTER the dive.
You could also do the same exercise with a full AL80 (of any sort) and then add six pounds to the figure to get *basically* the same number.
Of course, that formula only applies to single tanks...
Last point here: All of my numbers above are using a bp/wings. Many other BC's have "inherent buoyancy;" that is, the BC itself is actually slightly buoyant, and thus it requires a little more additional weight to offset.
IMHO, if you're diving with 18 pounds in a 3 mil, salt water, and an AL80 tank, you might be overweighted a little... But I've seen much worse.
Remember, diving with as little weight as possible is to your benefit... Not only do you have less weight to push around (and walk around with on the surface) but you have less air in your BC, effectively necessitating a smaller "hole" to push through the water. in other words, swimming becomes easier, and your air consumption drops. There's also the HUGE benefit that since you have less air in your BC, depth changes affect your buoyancy less... In other words, you don't have to dump or add air nearly as often. This is a major key in achieving the "cave diver" buoyancy that everyone remaks about.
...But that's not the whole picture. Here's the detail:
I'm 6'1" and 220 lbs. Body fat, which is something that completely makes a difference (muscle is negatively buoyant, while fat is positive) is around 17%. That's on the low to mid average for your regular American male, I believe. If I maintained a lower body fat percentage, I'd need less weight. More body fat, and I'd need more. Therefore, your mileage may vary. For reference, in a pool with no gear on, my body is either negative or positive depending on how much air I have in my lungs.
A 3mm wetsuit can very in buoyancy from manufacturer to manufacturer. In salt water, I am about 8 pounds buoyant with my O'Neill in only a mask, fins, and snorkel... At the surface. Go deep, and that number falls.
I dive a backplate and wing setup, with my backplate made of stainless steel. It's six pounds negatively bouyant... With little difference between salt and fresh water.
I also dive with a 1-pound "lightweight" STA.
I exclusively dive with Luxfer AL80 tanks, rated at about -2 pounds negative in salt water with 3000 psi (77.7 cu ft) and about 4 pounds positive empty.
Again, with this rig, I'm perfectly balanced in salt water with six pounds on my hips, and no additional weight whatsoever in freshwater. By the way, I have enough "play" in there to don a 3 mil hood if I choose... So I could lose maybe one pound without a hood, if I really wanted to.
So... The bottom line is, in salt water, with a 3 mil and a "standard" AL tank, if you include my plate and STA, I'm balanced at 13 pounds. I could probably do 12 without a hood. In freshwater, I'd wear only my bp and STA, for a total of 7 pounds.
Keep in mind that there are many AL tanks out there with different buoyancy characteristics... Luxfer also makes a "compact" AL80 and a "neutral" AL80 which are designed to be more neutral when empty and much heavier when full. If I were using one of these, I'd need less weight - but I don't use them because I've found that it messes up my trim (puts my center of gravity too far back).
For more information about certain tanks and their bouyancy characteristics, see http://www.diverlink.com/gear/tankspecifications.htm
Also, someone already posted this... And I'll "second" it... The best way to find the "correct" amount of weight is to follow the guidelines in the PADI OW manual... Take your "normal" equipment, and use a near-empty (less than 500 psi) tank into the water. With a full breath of air and NO air in your BC, the waterline should cut cleanly across the centerline of your mask... While you're floating vertically and looking straight ahead.
Of course, that's a great way to figure out your buoyancy AFTER the dive.
You could also do the same exercise with a full AL80 (of any sort) and then add six pounds to the figure to get *basically* the same number.Of course, that formula only applies to single tanks...
Last point here: All of my numbers above are using a bp/wings. Many other BC's have "inherent buoyancy;" that is, the BC itself is actually slightly buoyant, and thus it requires a little more additional weight to offset.
IMHO, if you're diving with 18 pounds in a 3 mil, salt water, and an AL80 tank, you might be overweighted a little... But I've seen much worse.
Remember, diving with as little weight as possible is to your benefit... Not only do you have less weight to push around (and walk around with on the surface) but you have less air in your BC, effectively necessitating a smaller "hole" to push through the water. in other words, swimming becomes easier, and your air consumption drops. There's also the HUGE benefit that since you have less air in your BC, depth changes affect your buoyancy less... In other words, you don't have to dump or add air nearly as often. This is a major key in achieving the "cave diver" buoyancy that everyone remaks about.
OP
JohnCollins
Guest
You are a wealth of information. Yes the BF% is a big factor, and judging from your photo, you spend more time with the iron than I do. , unfortunately for me. Folks vary quite a bit in body density, which is the big factor here, because we're using some similar equipment. I suspect that buyoancy differnces due to body density differences is somewhat greater than due to equipment differences, but it's at least as important, I'm sure.
I'm also gratified to see that this is shaping up as a fairly normal distribution. . .albeit for much too small a sample to be considered significant. . .but look at the spread of responses
2-3-3-6-3-4-2
eight on one side, nine on the other side of the middle response group, and the mean, median, and mode appear to all fall in that same group, as well (yes, I'm a geek).
JPC
, unfortunately for me. Folks vary quite a bit in body density, which is the big factor here, because we're using some similar equipment. I suspect that buyoancy differnces due to body density differences is somewhat greater than due to equipment differences, but it's at least as important, I'm sure.I'm also gratified to see that this is shaping up as a fairly normal distribution. . .albeit for much too small a sample to be considered significant. . .but look at the spread of responses
2-3-3-6-3-4-2
eight on one side, nine on the other side of the middle response group, and the mean, median, and mode appear to all fall in that same group, as well (yes, I'm a geek).
JPC
conchnclyde
Registered
- Messages
- 37
- Reaction score
- 0
Alot of good advice from this thread, but the bottom line is that you should find your own buoyancy to determine how much weight you need. I have found that I can actually dive with less weight on, than when I first started diving (I found this out by accident). I typically used about 16 lbs for my 5' 11" frame, and 200 lbs to boot (AL80 and 3mm shorty in salt water).
Several years ago, while doing some dives in Key Largo, for AOW dives, a DM had us go into the water with only 10lbs to check our buoyancy, and I did the entire dive (max 60') at that amount of weight (AL80 and 3mm). To confirm that amount of weight, I was diving in Aruba, and accidently went into the water with 8lbs, thinking that I had 12lb (AL80 and 3mm shorty), I noticed that I had some trouble descending, but after I got down around 20ft, I had no problem the rest of the dive (max 65ft). I learned alot that dive regarding breathing and buoancy, and I had no problem at the safety stop at 15ft. I felt much more free on that dive, but also learned alot about necessary weight while diving.
I think that it is a personal issue, and with some experimenting, the optimum amount can be figured for your frame, mass. The PADI Buoyancy Test is probaly the simplest method for acheiving desired weight necessary to be neut. buoyant. I have always heard that it is good to be just slightly pos. buoyant.
Safe Diving!
Clyde
Several years ago, while doing some dives in Key Largo, for AOW dives, a DM had us go into the water with only 10lbs to check our buoyancy, and I did the entire dive (max 60') at that amount of weight (AL80 and 3mm). To confirm that amount of weight, I was diving in Aruba, and accidently went into the water with 8lbs, thinking that I had 12lb (AL80 and 3mm shorty), I noticed that I had some trouble descending, but after I got down around 20ft, I had no problem the rest of the dive (max 65ft). I learned alot that dive regarding breathing and buoancy, and I had no problem at the safety stop at 15ft. I felt much more free on that dive, but also learned alot about necessary weight while diving.
I think that it is a personal issue, and with some experimenting, the optimum amount can be figured for your frame, mass. The PADI Buoyancy Test is probaly the simplest method for acheiving desired weight necessary to be neut. buoyant. I have always heard that it is good to be just slightly pos. buoyant.
Safe Diving!
Clyde
diveski01
Contributor
A LOT of recreational divers dive with too much weight. A lot don't know to or don't bother to do the weight check at 20ft w/ 500 PSI to verify proper weighting. A lot have a mental block (like me) about how much they "need" to get down. I try to take off a pound or two every so often (same equipment/dive site) to see if my weighting is too much. As my comfort level increases the amount of weight I think I need seems to decrease
SeaJay
Contributor
I'm flattered. The only reason I know this stuff, though, is because I just learned it. There are many more educated and experienced divers here.
Not many are as verbose as me, though.
Very cool... Statistics!
How are you compensating for the different body types and different gear configurations? Or are these just raw stats?...And did you put me down for 13 pounds or six? I'm not sure really how to properly translate that...
OP
JohnCollins
Guest
I figured you'd vote yourself. Use the weight of the BP, of course, and what you wear with a 3mm.
This is still looking very "normal" -- 12 in the middle group, ten on one side, nine on the other, at 31 responses.
Differences in body density and equipment "all come out in the wash" if we get a large enough number of responses. . .that is no reason to assume they trend in any direction, but are random, differences.
So I'm a little high, but not anything worth worrying about, if we can believe the numbers. Also, I agree. . .I may lose weight with experience with this suit. Most of the problem getting down occurs in the first 20 feet. Next dive, I'll get very picky about that 15-20 foot hang with 500 PSI. I wouldn't be surprised if I drop a couple pounds.
This is still looking very "normal" -- 12 in the middle group, ten on one side, nine on the other, at 31 responses.
Differences in body density and equipment "all come out in the wash" if we get a large enough number of responses. . .that is no reason to assume they trend in any direction, but are random, differences.
So I'm a little high, but not anything worth worrying about, if we can believe the numbers. Also, I agree. . .I may lose weight with experience with this suit. Most of the problem getting down occurs in the first 20 feet. Next dive, I'll get very picky about that 15-20 foot hang with 500 PSI. I wouldn't be surprised if I drop a couple pounds.
-hh
Contributor
- Messages
- 1,020
- Reaction score
- 245
Suits will give up a few pounds very quickly as they break in. You think its your better fitness/skill, until you get a new suit
And as you pointed out, differences between BC's can also make for a big difference. The weight of the plate on a BP/Wings combination is a typical place-holder. Interestingly, I recently tried a Knighthawk and found that it required double my normal amount of lead (10lbs vs. 5lbs) as compared to my ancient Tusa Jacket BC. Guess it was all of that "rugged" nylon for stuff like the weight integrated pockets and all that that was trapping air.
-hh
Similar threads
