Stainless BP vs Aluminum pool test vs sea

[drummerc]

Hi,

I just purchased my first BP/W (DGX starter kit). I ended up choosing stainless steel for the extra weight and because it seemed like most people like diving it and I have luggage capacity for it. After setting up my harness I threw it all together and put on an AL 80 with about 2k psi in it and went into the pool. I was wearing a 4/3 full suit which is what I want to dive with in thailand.

Unfortunately, when I checked my buoyancy by dumping my air and holding my breath, I sank to about the top of my head in the pool with no weight at all on. My question is, when I dive salt water (which is 100% of my diving), will the buoyancy difference be enough that I will be slightly positive with no added weight, or should I swap to an aluminum backplate?

I have about 50 dives and am rescue certified, so I’m not super new to diving, but I have never used a BP/W setup before. I would love to have like 2-4lb of ditchable weight for safety. For reference I’m 5’6” 160lb male using 3mm or 4/3 wetsuit always diving tropical salt water.

Thanks!

 

[johndiver999]

I would not have bought a SS plate. But it does not sound like you are really overweighted, even for freshwater, so saltwater should allow you to wear 3-6 lbs of lead. The problem will arise if you don't wear a suit and/or want to use a steel tank.

 

[Eric Sedletzky]

I don't currently as the water is a bit too cold to dive with a 4/3. I'm mostly diving on vacation and my wife refuses to dive cold water, so I also lose my buddy. I'm thinking I'll just keep the SS plate. Might freeze my butt off and do a proper weight test in the ocean since its not horribly far

I wouldn’t dive in San Diego in a 4/3, that requires a 7mm.
I’m just saying, enjoy what you have in San Diego, you live in a premium dive destination!
Keep the stainless plate.
Even with a 3 mm in the tropics, you could make it work with an Aluminum 80.
The true test of perfect buoyancy is when you can hold your 15’ safety stop with no air in your bc and your tank on reserve.
Adjust your added weights to achieve this and you’ll have it perfect, whatever that number happens to be.

 

[drummerc]

I wouldn’t dive in San Diego in a 4/3, that requires a 7mm.
I’m just saying, enjoy what you have in San Diego, you live in a premium dive destination!
Keep the stainless plate.
Even with a 3 mm in the tropics, you could make it work with an Aluminum 80.
The true test of perfect buoyancy is when you can hold your 15’ safety stop with no air in your bc and your tank on reserve.
Adjust your added weights to achieve this and you’ll have it perfect, whatever that number happens to be.

Oh I didn't mean actually dive, just throw all my gear on, wade out into the water for like 10 mins of fiddling with weights to get a good starting level and then come back in. I was thinking of just walking out into the bay until its like 7' deep and just going up and down a foot or less until I have it dialed to where I like it and verify that I'm not going to be negative with no lead. Shouldn't be TOO cold for a quick dip. First vacation dive I'll dial weights in at the safety stop with a tank at ~500psi.

 

[Valerii Vakshul]

I’m not sure I follow your post, are you referencing the 6 pounds of air that can be consumed from an AL80?

Your reset weight should be no less than the weight of the gas you would consume if you completed the dive.
Why should it be resettable - because if at the beginning of the dive, having descended to a depth (in case of a BC failure) you will be forced to ascend - you need to lose weight, the loss of which will allow you to become neutrally buoyant.
Having become neutral, you will be able to ascend (with a faulty BC (empty)) and even make a safety stop

 

[happy-diver]

Lucky you've probably been eating with your wife for a while and don't need the practice

But me when I take a new chick to a restaurant we go, get comfortable, look at the menu
then, when we are all set up and happy, we leave, ready for our actual booking tomorrow

 

[lexvil]

I think the wetsuit is a bit thick for Thailand.

 

[DivingSD]

Your reset weight should be no less than the weight of the gas you would consume if you completed the dive.
Why should it be resettable - because if at the beginning of the dive, having descended to a depth (in case of a BC failure) you will be forced to ascend - you need to lose weight, the loss of which will allow you to become neutrally buoyant.
Having become neutral, you will be able to ascend (with a faulty BC (empty)) and even make a safety stop

Along this logic you would actually want to account for both the weight of your gas and the lost buoyancy from compression at depth. Ideally I think a balanced rig would never be too negative to swim up or otherwise include redundant buoyancy like a dry suit. Ditching weight at depth seems like it should be way down the list of contingency plans. Ditching it at the surface could be more valid in some cases.

 

[inquis]

Along this logic you would actually want to account for both the weight of your gas and the lost buoyancy from compression at depth.

No, since you wouldn't be neutral at the safety stop if you did, and it's just not necessary. Kicking and lung volume can deal with that. Even my XL 7mm wetsuit would lose a mere 5 lbs at 100 ft *relative to its buoyancy at 15 ft*. Wikipedia has a nice summary of some testing that has been done on this topic. Lake Hickory Scuba has a YouTube demo using his 7mm suit.

 

[DivingSD]

No, since you wouldn't be neutral at the safety stop if you did, and it's just not necessary. Kicking and lung volume can deal with that. Even my XL 7mm wetsuit would lose a mere 5 lbs at 100 ft *relative to its buoyancy at 15 ft*. Wikipedia has a nice summary of some testing that has been done on this topic. Lake Hickory Scuba has a YouTube demo using his 7mm suit.

Agreed. My only comment is that you will be obviously carrying extra weight at the beginning of the dive at depth based on gas not consumed and compression. Ideally you would be able to swim up with that extra weight or have redundant buoyancy. Ditching that extra weight at depth isn’t ideal.

 

[Valerii Vakshul]

Согласен. Единственное, что я могу сказать, так это то, что вы, очевидно, будете нести дополнительный вес в начале погружения на глубине, исходя из неизрасходованного газа и компрессии. В идеале вы сможете всплыть с этим дополнительным весом или иметь избыточную плавучесть. Сбрасывать этот дополнительный вес на глубине не идеально.

Agreed. My only comment is that you will be obviously carrying extra weight at the beginning of the dive at depth based on gas not consumed and compression. Ideally you would be able to swim up with that extra weight or have redundant buoyancy. Ditching that extra weight at depth isn’t ideal.

Leaving the depths urgently (having full weight = gas + cargo) is not an ideal situation. You will have to give up a lot to get the opportunity to rise. And it will not be cold-blooded. To rise and not bend - this is the task and its condition and solution must be considered in advance.