Considerations around switching to a BP/W

[tbone1004]

depends on which mfg, what the fill pressure is etc. In a drysuit, 3mm, or 5mm, you should be OK. Marginal, but OK.

 

[stuartv]

Yes, the DSS rig will also cost me A LOT on shipping and duties.
The VDH plate looks nice but I would prefer a SS for the additional distributed weight.

That was my thought, too, in originally getting the SS plate. And it has been great when diving salt water in a 3/2 suit with a single steel 120 (15l). I need no additional weight. But, in a rash guard only, it would be heavier than necessary. And with an AL80, I still need additional weight.

So, after diving it that way for almost 2 years, I'm now thinking that the VDH plate will be more streamlined (because it's flat with no ridge to perch the tank on top of). With a rash guard and steel tank, I won't be overweighted (or at least not by as much). With my 3/2 suit, I will probably end up with 2 x 2# weights in trim pockets on a tank strap. And if I'm somewhere where I'm renting, I'll end up with maybe 2 x 5# weights in the trim pockets instead.

As I only have 1 real scenario where the weighting is just right with only the plate I am increasingly less concerned about needing to use 2 small trim pockets.

BUT, if you really want a SS BP, I will say that I got a Blue Reef SS plate a few months ago. It was on sale on LeisurePro for $49.95. I made it my dedicated plate for doubles and I am perfectly happy with it. It is not as flat as the DSS plate, which is a little nicer for doubles, maybe, but not quite as nice for a single tank, as it would position the tank just a little further from your body. not sure the difference would be noticeable, though.

The DSS plate has rubber grommets (for lack of a better term) in all the slots where the 2" webbing passes through. That is nice in that it protects the webbing from rubbing against a steel corner. And the grommets have a little internal flange that grips the webbing so it keeps the webbing from pulling through the slots easily. That is nice in that it keeps them from getting accidentally out of adjustment. But, at the same time, it's a pain when you do want to adjust the straps (e.g. when going from a thin wetsuit to a drysuit with undies). Adjusting the shoulder straps/waist belt is a lot easier on the Blue Reef plate.

The DSS plate has holes drilled and tapped to allow mounting of the DSS weight plates. I have a set of those plates. They are nice for diving single AL80 tanks as I require no additional weight, even with a 3/2 wetsuit. But, over time my weighting requirements have come down and now those plates work fine but I am carrying more weight than I need. You can't really just use one weight plate, so my options are be over weighted with an AL80 or take the plates off and add back half the weight in trim pockets. So, again, if you have a scenario where the bolt-on weights make your rig exactly the right weight to not need any additional weight, then they are great (but expensive!). But, if you are going to have to add weight anyway, then what's the point? The only really good use I can see is if you're diving single tanks in a drysuit where you really need a lot of weight. In that case, having those plates instead of an additional 8# of lead on your belt or in trim pockets might be kind of nice. For me, if I'm diving dry, I'm diving doubles, so that's not really a consideration for me. Especially since the bolt-on weights are only for use with single tanks.

If you can find a UK retailer for the Blue Reef plate, that might save you a ton of money and work out just as well for you. Or, really, probably just about any brand of plate. A bent stainless steel plate is not rocket science. The DSS plates are really well-made and the size options are invaluable for people who are big or small enough to need them. But, for average-sized folks, a "normal" size BP works and only you can decide if the DSS plate features (flatter, rubber grommets, holes for bolt-on weights) are worth the extra money to you. I'm 6' 1" and 225# and the BR plate size is working fine for me. My DSS plate is a size Large and I don't notice any difference in actual usage.

 

[rombre]

depends on which mfg, what the fill pressure is etc. In a drysuit, 3mm, or 5mm, you should be OK. Marginal, but OK.

That's all I need I want to cover 3mm and 5mm with Alu / Steel tanks of 12l and 15l, i.e. all my warm water diving. If it then also works with a 5mm + hooded vest, even better (and should cover even slightly colder places usually requiring a 5mm / 7mm)
Why does the combination of exposure suit and tank matter though?

Isn't the question for the lift required?:
A) Does the rig float with full cylinder (Only BP/W, reg and cylinder matter, i.e. -6 -2 -8 = ~ -16)
B) Does the wing have enough lift to make up for my maximum increase in buoyancy from wetsuit compression (i.e. only wetsuit matters - for a 5mm that should be ~ -10mm)

 

[tbone1004]

no.
A is correct
B has to also add in the weight of gas in the tank. I.e. wetsuit buoyancy + weight of gas since those are the two things that it has to compensate for as they are the variables

 

[rombre]

BUT, if you really want a SS BP, I will say that I got a Blue Reef SS plate a few months ago. It was on sale on LeisurePro for $49.95. I made it my dedicated plate for doubles and I am perfectly happy with it. It is not as flat as the DSS plate, which is a little nicer for doubles, maybe, but not quite as nice for a single tank, as it would position the tank just a little further from your body. not sure the difference would be noticeable, though.

Main reasons for SS for me are that I should be able to get towards very little required additional weight on most of my warm water dives - potentially even at some point to 0 in 3mm. Generally I hate (heavy) weight belts and I could surely get rid of them and only have a few lbs as trims or a pretty light weight belt.
Also when later buying a larger wing in addition and doing dry suit diving, the SS plate reduces the required weight quite a bit.

Thanks for the Blue reef recommendation (and all your detailed and always helpful background info!) - will have a look at it, but given my - non existent experience with BP/Ws - I might prefer to buy everything together at this stage.

 

[rombre]

no.
A is correct
B has to also add in the weight of gas in the tank. I.e. wetsuit buoyancy + weight of gas since those are the two things that it has to compensate for as they are the variables

That is based on the assumption that you want to be roughly neutrally buoyant at the safety stop with (almost) empty tank and would be more negatively buoyant at the start of the dive? Difference of a full to an empty tank seems to be generally around 7lbs, i.e. the max in this calculation would be:
-10 lbs (5mm wetsuit compression)
- 7 lbs (gas)
=> -17 lbs?

 

[stuartv]

To add to what tbone said, the two criteria for wing lift are, can it lift you when you're at your heaviest? And, can it float your rig at the surface if you need to take it off?

You're at your heaviest at the start of your dive, when you reach your max depth. Start of dive means your tanks are full. A bigger tank means you're more negative (since the idea is to be neutral at the end when the tank is empty-ish). A thicker wetsuit crushes more at depth, so when you get to max depth, it has lost the max buoyancy. Put those together and you are at your most negative at the start, when you get to the bottom. 9 # of gas in a single 120 plus, say 10# of lost buoyancy from 7mm suit crush means being 19# negative at the start, when you get to the bottom. Of course, the number for suit crush is made up and totally depends on the diver and the suit. If you're diving dry then you don't account for suit crush, you account for how much buoyancy you could lose if, say, you have a replaceable neck seal and it just blows off. If you're wearing thick undies and the air in the suit is giving you 20# of positive buoyancy (which you have counterbalanced with large amounts of lead), then you would calculate on the possibility to lose 20#. So, with 9# of gas, you'd want at least 29# of lift available.

Most amount negative at depth or most amount the rig is negative by itself (again, at the start when the tanks are full). Whichever number is greater is how much lift you need, minimum.

Some will say that for your dry suit calculation, if you have 20# of lead on a belt to counteract your suit's buoyancy, and the suit blows out, you can ditch the 20# belt, which means your wing doesn't have to be big enough to compensate for that. Personally, I'd rather have a bigger wing than a plan that depends on ditching my weight belt. And, if you attach that weight to your rig instead of wearing it on a belt, then the point is moot. The wing needs to be enough to float your gas (at the start) plus all the rest of that weight.

 

[stuartv]

That is based on the assumption that you want to be roughly neutrally buoyant at the safety stop with (almost) empty tank and would be more negatively buoyant at the start of the dive? Difference of a full to an empty tank seems to be generally around 7lbs, i.e. the max in this calculation would be:
-10 lbs (5mm wetsuit compression)
- 7 lbs (gas)
=> -17 lbs?

Difference is gas just depends on how much gas, not really the size of the tank, per se. An 80 holds about 6 # of gas. A 100 is a bit under 8. A 120 is more like 9.

 

[rombre]

So I guess the summary is, that a 20lbs should in practice be fine for all my warm water plans (i.e. 3mm / 5mm / 5mm + hooded vest; 12l / 15l alu / steel tanks).

 

[tbone1004]

yes, but it is unlikely to have a lot of lift to keep your head high and dry when at the surface with the big tanks. Do not expect it to float you like an otter like the jacket BC's do. As long as you have managed that expectation it will be fine. I prefer to have a bit more lift to be able to get my head clear out of the water if I have to which is why I use the LCD30 for all of my single tank diving, but a 20lb wing is more than enough for the actual diving portion