Buoyancy check help.

[danieldale]

I'm 6'2" 200 lbs. 3mil full wet suit c/w booties in salt water.Unsure of tank size and material used on this particular dive boat. How much weight should I start with; and when I do a buoyancy check [probably with a full tank]should I float at eye level holding my breath is that enough lead when tank is almost empty to hold me level for safety stop?

Am I correct with my calculations?
3 mil wet suit and booties 6%------12 lbs.
salt water add 6.5 lbs.
total..........................................18.5 lbs
if 80 alum add 5 lbs.
steel add 0 lbs or possibly remove.
does this sound right and if it is lets say alum then total 23.5 lbs when doing my check should I still be at eye level with 23.5 lbs. sorry for the ramble would appreciate your help.THANKS

 

[idocsteve]

I'm 6' 1" and I weigh about 225-230 depending on how good I've been with the exercise.

3/2 mm full weight suit in salt water with an AL80 and a pony tank, I use 10 lbs of weight.

Best way to check your weighting is start with your best guess and spend some time at the surface. Yes you should float about eye level with a full breath and an empty BCD on the surface but the best way is to double check your buoyancy at your safety stop with a tank that's closer to empty than full.

 

[paddler3d]

I'm 6'2" 200 lbs. 3mil full wet suit c/w booties in salt water.Unsure of tank size and material used on this particular dive boat. How much weight should I start with; and when I do a buoyancy check [probably with a full tank]should I float at eye level holding my breath is that enough lead when tank is almost empty to hold me level for safety stop?

Am I correct with my calculations?
3 mil wet suit and booties 6%------12 lbs.
salt water add 6.5 lbs.
total..........................................18.5 lbs
if 80 alum add 5 lbs.
steel add 0 lbs or possibly remove.
does this sound right and if it is lets say alum then total 23.5 lbs when doing my check should I still be at eye level with 23.5 lbs. sorry for the ramble would appreciate your help.THANKS

A lot going on there...

Likely you're going to be using an AL80. When you tank is full at the beginning of the dive, with no air in BC, you should be able to hold yourself at eye level with lungs full. Then add around 5#'s. Of course this is more accurate if you do it at the end of your dive with around 500psi. But it will work.

23# sounds real heavy. 10-12#'s should be closer and still that may be heavy.

 

[idocsteve]

AWhen you tank is full at the beginning of the dive, with no air in BC, you should be able to hold yourself at eye level with lungs full. Then add around 5#'s.

I was in complete agreement with you right up until you added another 5 lbs.

 

[paddler3d]

I was in complete agreement with you right up until you added another 5 lbs.

Tank is full...BC empty...Lungs full...float at eye level.

Assume it is an AL80. They have roughly a 4-5# swing. We want to be neutral at the end of the dive when the tank is more buoyant because we inhaled all the air.

If you don't add the weight of the swing, you're going to have one hell of a time holding that SS.

 

[idocsteve]

Tank is full...BC empty...Lungs full...float at eye level.

Assume it is an AL80. They have roughly a 4-5# swing. We want to be neutral at the end of the dive when the tank is more buoyant because we inhaled all the air.

If you don't add the weight of the swing, you're going to have one hell of a time holding that SS.

You are correct. Not sure what I was thinking there.

 

[paddler3d]

You are correct. Not sure what I was thinking there.

Whew...you had me freaked out there!

The joys of multitasking and ScubaBoarding!

 

[scubafanatic]

1) ask the dive boat what tank type/capacity you will be using, in advance of your trip.
2) what lift capacity wing/BC are you using....as in if you accidentally overweight yourself, will you become a scuba lawn dart ?
3) any chance you can do a predive weight check, say in a local pool ?

 

[paddler3d]

3) any chance you can do a predive weight check, say in a local pool ?

Unless the pool where your doing the check is salt, you're still not going to be able to nail it right on.

If you going to a place where it is salt, you're more than likely going to have AL tanks as rentals. They aren't going to do steel tanks for rentals. Too expensive and steel rusts. The only places I've seen AL100's you've got to request them. Most likely it is going to be an AL80.

Ask the DM when you get there. Keep in mind, new divers need more lead for some reason, whereas experienced divers don't.

 

[JohnB47]

My guess is 18-19 pounds. That is: 8.5 pounds for the suit, 5 pounds for your body floating in seawater, and 5 pounds for the positive buoyancy of the empty AL80.

If you do a buoyancy test in fresh water, and want to convert it to salt water equivalent: add weight until you are neutral in the water (just under the surface), then get out and weigh yourself and all your gear (you can weigh it separately and add). Whatever the total weight was, you must have displaced an equal weight of fresh water at 62.4 pounds per cu. ft. in order to have neutral buoyancy, so divide the total weight by 62.4 to find the volume in cu. ft. When you get into salt water, which weighs 64 pounds per cu. ft., your buoyancy will be positive by the additional weight of the salt water, (64 - 62.4) x the displaced volume. That works out to 0.0256 times the total weight. However, you still have to account for the weight of the air in the tank. So you have to add the 0.0256 x the total weight (to account for the salt water) PLUS the weight of the air, which is about 7.5 pounds per 100 cu. ft. (6 pounds for an 80 cu. ft. tank). That should get you pretty close.