Considerations around switching to a BP/W

[dumpsterDiver]

To be more clear, you want to avoid diving a rig that is more negative than necessary. If you pick some configurations, (and you are not fat) you will be carrying zero ditchable lead and if you have a BC failure, you will be stuck on the bottom, heavy with no way to ascend without kicking really hard.

So as mentioned by others, large steel tanks and really thin suits can be a problem and add a steel plate and the configuration is unsafe... something much more important than using a tiny wing.

A 5 mm suit could loose about 15 or 18 lbs of lift at depth, a big steel tank can swing like 9 lbs (roughly) from full to empty, so to address that potential swing, would require maybe 25 lbs of lift alone. It is not a good feeling to be wearing a thick wetsuit at 90 feet and having the BC completely filled and burping air out the Over pressure valve - every time you come up a few feet. It makes me nervous like the darn thing is going to pop. I don't like having to swim around with the BC full to the max.

 

[Lorenzoid]

The scenarios you are describing are pretty much exactly what I'm looking for (5mm + steel, 3mm/5mm + AL). Very helpful, thank you.

You're welcome. I arrived at the plate and wing combination (steel plate, Torus 26) that I believed would suit the two types of dives I mentioned after all of two emails back and forth with Tobin. Perhaps you're over-thinking this

 

[stuartv]

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.

CAN'T cover warm water diving with one plate? Well, I guess that's a matter of opinion. It seems pretty obvious to me that one lightweight plate (aluminum, Kydex, or skeletonized SS like a Dive Rite XT) will work just fine for warm and cold water.

I've dived my 3/2mm suit, SS BP, and a single steel 120 numerous times. Worst case scenario is get to the bottom at the start and have the inflator elbow on the wing break off or rip off the wing. That would mean a big hole at the top of the wing and no way to put air in it. In that case, if I assume my wetsuit has crushed down to giving me zero buoyancy it means I'm roughly 18# negative. I believe I could swim that up to the surface. But, I don't expect to have to do that. I carry a DSMB with 30# of lift. And I dive with a buddy. Either one by itself should be enough to get me to the surface without having to do 100% of the work to swim the rig up by myself. And the chances of a total wing failure during a dive are so slim that it's a chance I'm willing to take.

Any choice you make is going to involve a compromise. You can go the same way that anyone with an integrated BCD has gone - compromise by having a bigger wing than you need most of the time, with a lighter rig and more weight in pockets or on a belt (but the ability to always be weighted properly and never overweighted). OR, compromise the other way and use a SS BP and have some scenarios where you would be over weighted. But, since a SS BP is roughly 4# heavier than an AL plate, that means you're only going to be 4# worse off than with an AL plate, at most. 4# of weight difference is unlikely to be the margin that kills you. But, that is certainly just the opinion of one relatively inexperienced diver (i.e. me).

If you want to always have the absolute minimum additional lead on a belt or added to your rig, then get a SS BP.

If you want to always be able to be weighted optimally, in any conditions, get a lightweight BP. If you want the closest possible weighting to "ideal" while diving a steel tank in board shorts, get the lightest BP available - the DSS Kydex. You can always add weight to your rig. But, you cannot take weight off a SS BP.

 

[stuartv]

We basically reached the conclusion that this "normal holiday diving" profile more or less requires 2 different backplates + a wing (+ a separate wing if I wanted to use it in colder water as well). That's a lot of different gear ...

It only REQUIRES all that if you nitpick down to the last ounce of drag. Otherwise, get the lighter weight plate and the bigger wing and it will work fine for all your scenarios - better than the integrated BCDs everyone else on the boat are using.

Put 4 - 6# of weight in trim pockets on a tank band and it will dive just like a SS BP. The bigger wing (e.g. the Torus 26 I suggested yesterday) will work fine and you are extremely unlikely to notice the difference in drag between it and an LCD20.

 

[andy350z]

And then people say that BP/Ws are not a complicated topic
The summary is basically:
- For my warm water diving a 20lbs looks like a good choice generally, however is not ideal with 15l tanks (which is what I dive most of the time in alu or steel). There a 30lbs would probably be a better choice
- For cold water Tobin told me, that a 30lbs might not be enough and it could very well be that I'd need a 40lbs

If you are using the same tanks why should the water temperature and suit make any difference to the lift required.

You shoud be diving a balanced rig (see here for an explantion DIR-diver.com - How much lead?) in all of situations. The extra weight you carry when using a dry suit is off set by the extra boyancy the suit has.

The function of the wing is offset the weight of gas you will consume during the dive. Therefore you only need to change the wing when you change the volume of gas you are diving with.

For example I dive the following setups:

1) Double 12L steel with a drysuit, for this I use a 45lb lift wing.
2) Single 15L steel with drysuit, for I switch to 30lb lift wing. (also enough for 15L + 7l stage)
3) Single 10L aluminium with shorts and t-shirt, still a 30lb

I only change my wing when the volume of gas I'll be using changes. I change my weighting to compensate for the change in boyancy from thermal protection to balance the rig,

 

[stuartv]

Best option would still be the SS one if it works, as this would also be the far better choice for cold water (at a later stage).

It's only FAR better if you consider having an extra 4 # built into your BP a big deal in a scenario where you're going to have a fair bit more lead than that added to your rig anyway if you're wearing a drysuit and warm undergarments.

In other words, I would call it "a little nicer", not "a far better choice". It's 2 or 3 # less weight on each side of your belt.

In my drysuit, in cold salt water, with a single steel 120 I would use my SS BP plus about 14 # of weight. if I used an AL plate and had to have 18 # of weight on my belt instead of 14, it just wouldn't be that big a deal.

Like I said before, you have to pick your compromise. Use a SS BP and be a little overweighted in some scenarios or use a lightweight plate and carry some extra lead in trim pockets in other scenarios. To me, it's not a big deal, either way. I have a DSS Kydex plate because I got it used, for $20, not because I felt like using my SS BP and having that extra 5# or so was going to kill me.

 

[stuartv]

If you are using the same tanks why should the water temperature and suit make any difference to the lift required.

Because if your tank is 9# negative at the start of a dive and you dive in board shorts, then your wing really only needs about 9# of lift to keep you neutral at depth. Assuming you're properly weighted.

But, if you use the same tank and a 7mm wet suit, when you get to depth your suit could lose 15# of buoyancy, so at depth your wing would need more like 24# of lift.

If you use the same tank with a drysuit and thick undergarments you might put on even more lead than with your 7mm. If you get to the bottom and your neck seal blows out and you lose all the air inside, you might be carrying 25# of lead plus the 9# in your tank and need 34# of lift from your wing.

Of course the suit matters to the lift required. And the water temperature drives the suit choice, so it matters, too, indirectly.

 

[rombre]

Thanks a lot for all your help and patience, guys!

I think it will be a SS BP + Torus 26 then.
The (vast) majority of dives I do, is with 12-15l AL tanks, the other few with SS tanks (and 5mm) should then be ok as well as per the reports here.

 

[tbone1004]

I use SS plates for all single diving. If I'm diving without a wetsuit or with a thin wetsuit in fresh water, then I will try to find an AL80. This is what I was trained in. Is it overweight? Yes of course, but it's not so much that I can't keep the rig at the surface with a failed wing. If it's in salt water, then I'm perfect, so I just don't dive steel tanks in the salty stuff. I sink, so if you float or are closer to neutral, then you can probably get away with something like a Faber LP85 which is a little less floaty than an AL80, but not as sinky as most of the steel tanks.

The only time I use my kydex plate is with lighter weight doubles *LP72's etc* in a wetsuit or drysuit with almost no undergarments, or my heavy doubles. I don't use it with singles because I choose not to dive big heavy tanks where it would cause me to be overweighted.

appropriate sized SS plate with a Torus 26 will be a good decision for you at this point in your diving and will not be something that you will regret not going smaller.

 

[dumpsterDiver]

If you are using the same tanks why should the water temperature and suit make any difference to the lift required.

You shoud be diving a balanced rig (see here for an explantion DIR-diver.com - How much lead?) in all of situations. The extra weight you carry when using a dry suit is off set by the extra boyancy the suit has.

The function of the wing is offset the weight of gas you will consume during the dive. Therefore you only need to change the wing when you change the volume of gas you are diving with.

For example I dive the following setups:

1) Double 12L steel with a drysuit, for this I use a 45lb lift wing.
2) Single 15L steel with drysuit, for I switch to 30lb lift wing. (also enough for 15L + 7l stage)
3) Single 10L aluminium with shorts and t-shirt, still a 30lb

I only change my wing when the volume of gas I'll be using changes. I change my weighting to compensate for the change in boyancy from thermal protection to balance the rig,

Wrong. Wrong. The BC must compensate for suit compression and this is often more than weight swing in the tank. Sometime 300% MORE