Enough Weight?

[tboxcar]

Today I was in the 'pool' testing a few things on my BC, the last time I was diving was 6 weeks ago in the tropics (SE Asia), with no wetsuit and I was using 8 lbs. of weight, could have used a 'tad more' but this did it.
Today, in the pool, using the same gear (no wet suit either dive, although some polyeflin shorts and a thin rash guard were used overseas), I quickly realized I only had 4 lbs of weight to use, knowing that salt water is a 'bit more buoyant' I figured I was going to be too light.
I was very much surprised after getting in the water and dumping the air out of my BC, I quickly went to the bottom with never a 'hint' of not having enough weight.
How could this be? Salt water does not increase buoyancy that much more does it?
Any ideas or comments?

 

[SangP]

Salt water has a higher specific weight and you'll be more buoyant. Normally you'll need 2-6 lbs between salt and fresh. Eg, if you tried to scubadive in the dead sea you'll need a heck of a lot more weights LOL!

SangP

 

[cool_hardware52]

Today I was in the 'pool' testing a few things on my BC, the last time I was diving was 6 weeks ago in the tropics (SE Asia), with no wetsuit and I was using 8 lbs. of weight, could have used a 'tad more' but this did it.
Today, in the pool, using the same gear (no wet suit either dive, although some polyeflin shorts and a thin rash guard were used overseas), I quickly realized I only had 4 lbs of weight to use, knowing that salt water is a 'bit more buoyant' I figured I was going to be too light.
I was very much surprised after getting in the water and dumping the air out of my BC, I quickly went to the bottom with never a 'hint' of not having enough weight.
How could this be? Salt water does not increase buoyancy that much more does it?
Any ideas or comments?

Sounds about right to me. For every 40 lbs of diver and gear you need 1 additional lb of ballast in salt water vs fresh.

In other words if you hopped out of the pool and stood on a scale with all your kit, and it read 160 lbs, you'd need 160/40 = 4 lbs in salt water.

Salt water is about 2.5% denser than fresh. 1/40 = .025

Tobin

 

[fmw625]

I usually dive with 4# fresh water and 8# in salt water. Tried 6# once in salt water but couldn't get down. Don't forget that an AL80 tank is about 5# lighter at 500# than when full. You don't want problems holding 15 ft at your safety stop.

 

[rakkis]

The above posters are correct about needing 4-6 lbs more in salt water.

Your breathing will also affect your buoyancy at the surface. Perhaps you were more relaxed in the pool and didn't hyperinflate your lungs?

 

[tboxcar]

I do think it had a bit to do with being in the pool, as there is not too much to do in the pool, besides sink! There is not much chance to 'fill my lungs' up and float. This being the case I still find it interesting with this little weight!

 

[alhatten]

Your body bouyance can change day to day. I can shift 2 to 4 pounds by eating different foods. Everyone is a little different and you need to find the average that works for you. I personally prefer slightly neg but that is because I usually have students and we need to be pinned to the bottom. Then again I worked a dive boat and all the weights were given out to the paying customers so I went out light by 10 pounds. I had to constantly swim downwards, but it was do-able.

 

[Rogue_Diver]

It could be your tank. I know when traveling I use what they have--usually an AL 80. If you use a steel tank at home it would be a lot heavier.