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!

 

[Bob DBF]

It sounds about right, but I'd carry a couple of 2# weights for the first dive and do a real weight check at the end.

 

[Valerii Vakshul]

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!

In tropical salt water (as opposed to a swimming pool) you will have 2-3 kg of positive buoyancy.
You need a Kevlar back plate.
The Kevlar plate will add another 1.6 kg of positive buoyancy to any water.

 

[DivingSD]

I’m about the same with a SS plate and 3mm, slightly over weighted in fresh water and no weight needed in salt. Most of my fresh water diving is dry so that takes lead, and I don’t worry about ditchable weight otherwise because it’s well balanced.

 

[inquis]

At 160 lb + 35 lb tank+reg + perhaps 10 lbs for wetsuit+BP/W, your salt water weighting will be about 5 lbs over what you need in fresh water, all else being the same. This comes from the difference in water density (2.4%) times your total (dry-land) mass: you, tanks, lead, BP, etc.

 

[drummerc]

Thanks very much everyone. That few lb difference should be enough for me to keep the SS plate and not worry too much about ditchable weight. I plan on doing a weight check on my first dive anyway to dial it in.

 

[Eric Sedletzky]

Do you ever dive in San Diego?
That stainless plate is perfect for that.
In tropics with an aluminum tank you have to do the math. A stainless steel plate is 5.5 to 6 lbs.
An aluminum 80 ends up 3 lbs positive.
Your 4/3 requires what, 6 - 8 lbs.?
So maybe 3-5 lbs. extra on a belt in salt?
IDK, I dive freezing cold water in Norcal and San Diego would be a tropical paradise to me, and where ever you’re going is mythology so maybe I’m the wrong guy.

 

[Valerii Vakshul]

I’m about the same with a SS plate and 3mm, slightly over weighted in fresh water and no weight needed in salt. Most of my fresh water diving is dry so that takes lead, and I don’t worry about ditchable weight otherwise because it’s well balanced.

Gas weight = weight dumped. Remember this.

 

[drummerc]

Do you ever dive in San Diego?
That stainless plate is perfect for that.
In tropics with an aluminum tank you have to do the math. A stainless steel plate is 5.5 to 6 lbs.
An aluminum 80 ends up 3 lbs positive.
Your 4/3 requires what, 6 - 8 lbs.?
So maybe 3-5 lbs. extra on a belt in salt?
IDK, I dive freezing cold water in Norcal and San Diego would be a tropical paradise to me, and where ever you’re going is mythology so maybe I’m the wrong guy.

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

 

[DivingSD]

Gas weight = weight dumped. Remember this.

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