How much weight to add?

[Empty V]

I just weighted myself in my pool with a bp/w system and my spankin' new HP119 tank. I can't remember, is it 6lbs that you add when going to salt, and should I add a little extra because there is a 9lbs swing when it's empty?

Thanks to all for the help!

Billy

 

[texdiveguy]

To be very honest there is NO magic formula,,,,many factors come into play. As a 'general' rule 5-6lbs. would be a typical starting point. If you can do a few shore salt water dips to play with your new configuration,that would be best. You always want to be 1-2 lbs. on the heavy side as you fine tune.

 

[SteFord]

Six pounds is just right for me when I go from fresh to salt water. I usually dive with ST 100's or 120's. I use integrated weight in my BC but keep a handy "salt belt" for the briny dives. Your bouyancy has more to do with your body composition though, so you may need more or less than me. Best approach is to take extra weight and once you're in the water do a bouyancy check and remove any excess weight you may have. Hand it to your buddy for the rest of the dive and later you can discuss what a crappy SAC rate they have. Have fun!

 

[CompuDude]

The the extra swing weight of your tank should come into play, but that number will depend on what tank you are coming from. If you're coming from an HP100, where the swing is 8 lbs, the 9 lb swing of your HP120 is only 1 lb different. If you're coming from aluminum 80s, the difference is far more radical.

But now that I re-read this, nevermind, since you've already weighted yourself in the pool, I'd agree that 6 pounds might work as a starting point, and if you're worried, add another pound or two. A pound or two heavy won't be too horrible, and if you think you're heavy on your first dive, once you're in salt water, just leave a couple pounds off for the next dive and fine tune as you go.

Congrats on the tank, btw. I'm jealous...

 

[spectrum]

For your needs there are magic formulas, it's all physics as long as you had a good configuration with a known cylinder.

First when going to salt divide your entire diver weight by 40. That represents the difference in the densities of fresh and typical salt water (1.00 vs 1.026). A diver that dresses out pre-dive at 280 pounds would need 7 pounds. That's you and all your gear, including fresh water weights and cylinder.


As for the cylinder change look up the empty buoyancy values and the difference is your change. Odds are you are removing weight.
http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

Your net change will come from these two factors.

Here is a good summary: http://markfm.dynalias.org/Weighting.pdf

Pete

 

[AlaskaDiver]

Spectrum;
Nice answer & links.

 

[webhead]

HP steels - should still be negative when empty. So that changes the weight you need - i.e. less of it. I can do 4 lbs of lead with my HP 120. With a std 80, I need more like 14 lbs. And I'm a big guy.

 

[texdiveguy]

I would with respect to my NE diver offer up from experience that the sighted math. formulas are fun and will get you in a ballpark of were you need to be,,,but the real magic is in just getting in the enviroment you are diving in the gear configuration you are going to dive and working thru the wt. process,,,,5-6lbs. will put you very close with what info. you have provided us readers. There are no formulas that can get you dead-on,,,they are simply a tool and in most cases do not work as well as the method of getting in the water and experimenting.

 

[JDog]

"HP steels should still be negative when empty..." What weighs more a pound of gold or a pound of feathers? (Don't answer too quickly.)

 

[SparticleBrane]

I'm also going to throw this out there--if it's a 119, then it isn't technically a "HP" tank. It's either an E8-119 or an X8-119 made under the DOT exemption, but it isn't an HP tank.