Redundant Buoyancy

[OmarM]

Hey folks, I’m sure this has been addressed in some form on the forum already but I am looking for clarification on my specific situation.

I will be diving a new bp/w with a stainless steel back plate. By my calculations, I will not need to add any removable weight in order to be negative at any depth. The negative of this is that if for some reason there is a catastrophic BC failure, I wont be able to become positive by dumping weights.

Now the total kit is probably about 15lbs negative. The buoyancy of the wetsuit will offset some of that unless it’s fully compressed. Let’s assume it’s a best case scenario and I can swim up to the surface. I’m now still about 6 lbs negative if I’m wearing a 3mm full. I don’t know how hard it is to tread water in those conditions.

Should I be carrying a safety sausage or another flotation aid? Or is my buddy a sufficient source of redundancy.

 

[jgttrey]

15 lbs negative is a lot. Try swimming up 15 lbs of weight. 6lbs negative at the surface is a lot too.

You cannot rely on a wetsuit for buoyancy as it compresses at depth and over time. My 3MM sinks in a rinse bin (perhaps time for a new one).

If you really are that negative (which sounds a bit excessive even for SS BP), then you need to dive an aluminum BP.

You should carry a DSMB anyway. A sausage is not enough for that purpose and it lacks an OPV. You'd need to practice that skill and it's a poor substitute.

The other problem is being 16 lbs negative requires a ton of air in your wing, which just makes the dive suck. I think your priority ought to be getting your rig better balanced, starting with an aluminum plate.

 

[aviator8]

When you say 15lb negative are you sure you dont mean it weighs 15 lbs on land? you would need to put it in water and weigh it in water to get the negative weight in water. Are you including your tank in that calc?

 

[Fastmarc]

How did you arrive at your calculations?

Here is a tool that can help. There is good info in the instructions as well.

Optimal Buoyancy Computer

 

[Zef]

When you say your total kit is 15lbs negative.....how are you measuring that? Are you measuring in the air or in the water?

-Z

Edit: Looks like @aviator8 beat me to these questions.

 

[jgttrey]

I agree on getting terminology and data correct. I assumed he meant that he and his kit were -15 lbs in the water, which is no bueno.

But, the figures aren't making much sense. No 3mm wetsuit would add 9 lbs of buoyancy, which is what the post suggests.

 

[OmarM]

Thanks for the clarifying questions folks.

The manufacturer ball parked the offset of the kit as being 9lbs negative, in the water, without a tank. A full AL80 is about 3lbs negative I believe, so we're at 12lbs. I added 3lbs for the other miscellaneous gear, as well as a margin of error.

Now my wing has 30lbs of lift which I am confident is more then sufficient. It will support my rig both at the surface and at depth.

Assuming at depth the wing fails, and there is no wetsuit buoyancy provided. I am 15lbs negative without any air in my lungs. Im guessing a full breath is about 5lbs? That still leaves me about 10 negative. As some other responses have mentioned, that would be very hard to swim up. Even if I switch to an aluminum plate, that's still about 7lbs to swim up.

What do I do in that specific unlikely emergency? Shoot a DSMB and climb the line? Seems very difficult to do in a situation where I am sinking.

To those who mentioned shedding weight, How could I do that? I don't seem to have much extra anything besides the SS plate.

 

[aviator8]

I don't think swimming up 15lb with fins presents much of an issue. I have had to do surface tread tests holding that much weight over my head with no fins. Also remember that your tank is going to go from -3 to +3 lbs over the course of your dive. Between a buddy, a DSMB and your setup I would say you are good diving over a hard bottom.

 

[OmarM]

I don't think swimming up 15lb with fins presents much of an issue. I have had to do surface tread tests holding that much weight over my head with no fins. Also remember that your tank is going to go from -3 to +3 lbs over the course of your dive. Between a buddy, a DSMB and your setup I would say you are good diving over a hard bottom.

When you say over a hard bottom, would you say a wall dive is unsafe? I am doing a NAUI course in a few weeks and I wouldn't be surprised if one was a part of it.

 

[aviator8]

Any dive over no bottom is a more advanced dive in my mind, but I would worry more about currents than a catastrophic failure of my BC on a wall dive. If you maintain your gear, and keep it clean, and don't abuse it you are unlikely to ever see a major failure of your BC. Proper pre dive checks should catch 99% of other BC issues. Even if it did you could fin over to the wall and grab hold until you could get sorted with your buddy or get a DSMB launched. Keep in mind that almost all rec divers dive with non redundant bladder BC's.