Considerations around switching to a BP/W

[eelnoraa]

I agree with Tobin. The bp/w is not complicated at all (simpler in fact) if your expectation remain the same as buying a BCD, which is an not necessary optimal solution itself but work for almost all situations. BP/W can get complicated because the choices present. Choice to be optimal.

But I will say if this is your first BP/W, you probably don't need everything to be optimal. If I were you, diving warm water on vacation most of the time, but want an option to wear thicker suit when situation presents, I will get a AL/Kydex plate with a 30bl wing. AL/Kydex vs SS is 4lb difference only. Adding 4lb somewhere in the rig is very easy to deal with. A 30lb wing probably isn't as streamline as a 17lb, but it night and day improvement compare to a BCD already. A properly deisgn 30lb wing (Oxycheq) is very streamline, it gives you option to wear 7mm wetsuit for even a drysuit.

 

[stuartv]

For this, you can't really go wrong with any of the wings you have mentioned, so it's kind of a crapshoot.

You really think 17# is enough to float a SS BP, full steel 120 w/regs attached, harness with hardware, plus anything that might reasonably be attached?

The SS BP plus 120 is probably going to be at least 15# negative just by themselves.

 

[tbone1004]

do you really thing the hog 23 is?

 

[stuartv]

do you really thing the hog 23 is?

Yes. I have floated my rig (DSS SS BP + steel 120).

But, I was asking for the OP, to whom you said that any of his options would work, which included a Torus 17, and to whom I suggested getting a Torus 26. I think the 17 is too little for what he intends and the LCD 20 is marginal (given he wants a SS BP and wants to use steel 120s).

 

[rombre]

Rombre, if you plan to dive in warm water with *either* a buoyant al 80, *or* a negative steel tank you don't need two wings, you need two different plates.
Tobin

Some places I went to only had steel tanks (e.g. in Malta), many only have aluminum tanks, so I don't really have a choice there.
In my calculations I didn't get to a scenario where I would be overweighted with the SS BP and no additional weight (borderline on a 3mm with a big steel tank but again that's a something I will not dive in this combination). My calcs might be wrong again but for the 15l steel tank I got to:

5mm wetsuit +10
15l steel tank empty -1
reg -2
BP/W SS -6
Total: +1 + my inherent buoyancy (which is not small - in my calcs I got to ~ 5lbs), so +6 total

Where's my mistake?

 

[stuartv]

Some places I went to only had steel tanks (e.g. in Malta), many only have aluminum tanks, so I don't really have a choice there.
In my calculations I didn't get to a scenario where I would be overweighted with the SS BP and no additional weight (borderline on a 3mm with a big steel tank but again that's a something I will not dive in this combination). My calcs might be wrong again but for the 15l steel tank I got to:

5mm wetsuit +10
15l steel tank empty -1
reg -2
BP/W SS -6
Total: +1 + my inherent buoyancy (which is not small - in my calcs I got to ~ 5lbs), so +6 total

Where's my mistake?

Not sure who you're talking to or what you're questioning. If it was me, my point was that your wing should be able to float your rig, if you take it off in the water.

My steel 120s (15l) are about -9 # when full (at least one other brand/model is way more negative). A SS BP is -6. By the time you add a tank valve, harness webbing and hardware, regulators, a light or two clipped to your harness, etc.., the rig could easily be more than 17# negative by itself. So, a 17 # wing would not be enough to float that rig by itself if the tank were full.

If you used an aluminum BP and wore the extra weight that you needed on a weight belt, then the 17# might be fine.

 

[rombre]

Not sure who you're talking to or what you're questioning. If it was me, my point was that your wing should be able to float your rig, if you take it off in the water.

My steel 120s (15l) are about -9 # when full (at least one other brand/model is way more negative). A SS BP is -6. By the time you add a tank valve, harness webbing and hardware, regulators, a light or two clipped to your harness, etc.., the rig could easily be more than 17# negative by itself. So, a 17 # wing would not be enough to float that rig by itself if the tank were full.

It was actually directed to Tobin as he suggested I can't cover the warm water diving with one backplate.

For floating the rig my calca were very close to what you have - I got to -15. But for that purpose the 3lbs buffet from your calc to a 20lbs wing should be sufficient I assume? Understand that a 17/18 lbs might be stretching it.

 

[cool_hardware52]

It was actually directed to Tobin as he suggested I can't cover the warm water diving with one backplate.

For floating the rig my calca were very close to what you have - I got to -15. But for that purpose the 3lbs buffet from your calc to a 20lbs wing should be sufficient I assume? Understand that a 17/18 lbs might be stretching it.

Last time. Just because you have a wing that will float your stainless plate + full negative steel tank doesn't make it a good idea.

Being over weighted *sucks*

It increases greatly the consequences of a buoyancy failure.

Thin suits + stainless plate + negative steel tank = over weighted = BAD IDEA

OTOH using a lightweight plate with buoyant al tanks defeats one of the primary benefits of the ballast a Stainless Plate can provide *UP OVER* your buoyant lungs and along side a buoyant cylinder.

That makes using one plate in warm water for both negative steel tanks and buoyant al tanks problematic.

Tobin

 

[rombre]

Tobin,

Somehow my communication leads to constant misunderstandings between us
I understand that there are 3 aspects:
- can the wing float my rig
- can the wing make up for the potential buoyancy loss of the exposure suit
- make sure the bp/w (i.e. Backplate) does not lead to negative buoyancy without weights

For the first two the answer seems to be a 20 or 25 lbs wing.

For the third one I get your point re: overweighting. I am now trying to understand in what scenario that problem would occur (i.e. What is a "thin" suit in your explanation). As mentioned before, I won't dive a 15l steel with a 3mm wetsuit. I completely understand that this is problematic.
The big - and crucial - question for me is, can I do 5mm wetsuit + 15l steel (which is a scenario that I had and will have again) with a steel backplate. My caculation said it should be fine but I am obviously not an expert by any means - you are. What is your opinion there?

Last time. Just because you have a wing that will float your stainless plate + full negative steel tank doesn't make it a good idea.

Being over weighted *sucks*

It increases greatly the consequences of a buoyancy failure.

Thin suits + stainless plate + negative steel tank = over weighted = BAD IDEA

OTOH using a lightweight plate with buoyant al tanks defeats one of the primary benefits of the ballast a Stainless Plate can provide *UP OVER* your buoyant lungs and along side a buoyant cylinder.

That makes using one plate in warm water for both negative steel tanks and buoyant al tanks problematic.

Tobin

 

[cool_hardware52]

5mm suit on people of normal stature will be 8-10, maybe 12 lbs positive. Lets say it's +10 at the surface and ~+7 at 15 ft.

Typical negative steel tank, HP 100, LP95, HP120 etc. will be about -2lbs empty and ~-10 to maybe -11 full.

This diver will need a *total* of 7 lbs of things that do not float at 15 ft with an empty tank.

His tank will provide 2 lbs and his reg will provide ~2 lbs leaving him ~3 lbs short.

A medium SS plate and harness will be ~-6 lbs. That will over weight the diver by ~3 lbs.

Rig weight is 6 (plate and harness) + 2 (reg) + 11 (full bottle) = -19. -19 is borderline for a "20 lbs wing" A Fat fill, or "Y valve" or a bit of water in the bc and you run the risk of not being able to float the rig.

The solution is a lightweight plate. Using a Kydex plate the diver may need 1-2 lbs of lead. Rig weight is now ~-15.

Same diver using an al 80. with a SS plate:

Rig with full tank ~-10 lbs, Rig with empty tank ~4 lbs. Diver needs ~2-3 lbs.

Same diver using al 80 with light weight plate.

Rig with full tank -6 Rig with empty tank *0* Diver need 6-7 lbs of lead. 6-7 lbs on a belt with a buoyant "cork" of a tank between your shoulder blades can make horizontal trim difficult.

In warm water switching between negative steel tanks and positive al tanks dictates a plate change.

No doubt I'll be sorry I pointed this out.....

Tobin


Tobin