Halcyon 36 vs. 45?

[jplacson]

Izzy.. sorry, you're right... I misunderstood him... single tank, w/ 2 add'l on each side (dunno why this way though), and a pony

so that's 3 (AL80) tanks + a pony.

Anyway, AFAIK... you're NOT supposed to use your BC as an underwater elevator to ascend.

The BC is supposed to keep you neutral, and YOU fin upwards. Inflate only to help you float at surface.

From what I've read, you're supposed to be able to fin yourself up to the surface with your whole rig, on an empty bladder... just in case of bladder failure. Your rig isn't supposed to weigh you down THAT much. Since BCs are NOT life jackets.

Diving steel tanks is supposed to make things easier since all you have to compensate for now is your wetsuit... since most steel tanks are not as buoyant as AL80s when empty.

So basically, all the weight you're carrying is supposed to be just to sink YOU with your wetsuit... nothing more.

AL tank users have a tougher time since they'd have to add about 4# more for every AL80 tank to adjust for it when it's empty.

This is what I've gathered so far anyway.

Anyway, if you're still in doubt... I seriously think the 36 should be enough. More lift isn't always better. But if you really really want a lot of lift? I think OMS gives the most lift per $!

Don't they have a 95 or 100# bladder for about the same price as a Halcyon 27?

 

[JohnCollins]

Don Burke once bubbled...
Flooding a drysuit isn't the massive buoyancy problem some would lead you to believe. It takes almost three gallons of water to make up 25 pounds. If you're diving with a bubble that big in your suit, you've got other problems.

You don't "add weight" if you flood a drysuit, you lose only the buoyancy of any lost air. Water is incompressible, and also, water is neutrally buoyant in water, of course. You could pump up your dry suit with water like a balloon, and the more water won't make you need more lift. All the extra water it displaces weighs the same as the water it's filling with. You'll lose the buoyancy of the lost air, but no more, if you flood a drysuit.

Ships and submarines have ballast tanks they can alternately flood or fill with air. Now that changes the weight of the ship or submarine, and the displacement is unaffected, so the buoyancy is affected by changing weight. In a BC buoyancy is affected by changing displacment. But in flooding a BC you change the displacement and weight at the same time, but doing it with water, so it has no effect on buoyancy.

I don't even own a dry suit, I'm just a bit of a geek, I think.

 

[Genesis]

is a huge problem if you ever have one.

Even if you dive with the dump completely open (and you should) and use the wing for buoyancy (and you should) a serious flood (e.g. you catch it on something and rip it wide open) is a major problem precisely due to the loss of the air inside.

That is NOT a trivial amount of buoyancy that instantly disappears.

I typically dive 14lbs of lead with a single steel tank (roughly neutral); my plate and STA are another -8. So the SUIT is +22!

That is with the dump WIDE OPEN; I put in just enough air to avoid squeeze (proven by the fact that if I put in more, it simply bubbles out the open dump!)

If the suit floods catastrophically, all 22 lbs of that buoyancy are GONE!

Now in addition, I'm carrying 7.5lbs of gas if the tank is full (HP100); that makes me -30! Eeeeeeek! Can you say SINKS LIKE A STONE?

Now, if the suit floods, I want to be able to get back up to the surface and REMAIN THERE. A 30lb wing JUST BARELY makes that possible, but has no margin for rough conditions. A 45lb wing has sufficient margin for rough conditions.

Yes, I can ditch the weight belt on the surface, which is why the 30 is JUST enough to be safe.

A 27 would be insufficient.

BTW, the real fun is getting back out of the water with a flood. While the flood results only in the loss of positive buoyancy from the suit underwater, its total dead weight above the surface. Every gallon of water weighs ~8lbs.

You can trap a LOT of gallons of water in a ripped drysuit, and getting back out of the water in such a situation may be an extremely serious or even life-threatening exercise, especially if the seas are rough.

 

[David Evans]

Genesis once bubbled...
I typically dive 14lbs of lead with a single steel tank (roughly neutral); my plate and STA are another -8. So the SUIT is +22!

...If the suit floods catastrophically, all 22 lbs of that buoyancy are GONE!

Now in addition, I'm carrying 7.5lbs of gas if the tank is full (HP100); that makes me -30! Eeeeeeek! Can you say SINKS LIKE A STONE?

...Yes, I can ditch the weight belt on the surface, which is why the 30 is JUST enough to be safe.

A 27 would be insufficient.

Did you actually do the math on this?

You are -30# to start with, you say.

You are carrying 14# ditchable, you say.

30-14=16.

How, exactly, is a 27 pound wing insufficient to float 16 pounds?

-david

(p.s. - even if you dive with no suit, is your body positive or negative in salt water?)

 

[Don Burke]

JohnCollins once bubbled...


You don't "add weight" if you flood a drysuit, you lose only the buoyancy of any lost air. Water is incompressible, and also, water is neutrally buoyant in water, of course. You could pump up your dry suit with water like a balloon, and the more water won't make you need more lift. All the extra water it displaces weighs the same as the water it's filling with. You'll lose the buoyancy of the lost air, but no more, if you flood a drysuit.

Ships and submarines have ballast tanks they can alternately flood or fill with air. Now that changes the weight of the ship or submarine, and the displacement is unaffected, so the buoyancy is affected by changing weight. In a BC buoyancy is affected by changing displacment. But in flooding a BC you change the displacement and weight at the same time, but doing it with water, so it has no effect on buoyancy.

I don't even own a dry suit, I'm just a bit of a geek, I think.

John,

What did you think I meant by "a bubble that big"?

Actually, some designers interpret the main ballast tanks on a submarine as changing displacement, not weight. The math works either way. The ship does too.

 

[Genesis]

Did you actually do the math on this?

Yes. Did you?

You are -30# to start with, you say.

You are carrying 14# ditchable, you say.

30-14=16.

How, exactly, is a 27 pound wing insufficient to float 16 pounds?

Because ditching at depth is an UNACCEPTABLE AND FOOLHARDY PRACTICE.

You can NEVER know with certainty that you have ZERO buoyancy contributed by some device at depth - even from a drysuit flood. If you ditch at depth, you risk an uncontrolled ascent. There is exactly one situation where that risk is acceptable, and that is where you are OOA and unable to make a CESA - a situation that should NEVER happen if you are correctly weighted - but one in which the absolutely inescapable outcome, absent a ditch, is drowning. There is no other scenario where a ditch at depth is a reasonable answer to the trouble you find yourself in.

The entire idea of ditching at depth is, IMHO, moronic. It is something that I personally guard against by placing my weight belt UNDER my BP harness. It is thus difficult, but not impossible, to ditch at depth. It is quite easy to ditch on the surface, and if I need to, I am probably willing to ditch the KIT as well (if the wing is non-functional it is negative, and thus on the surface I have no need for it trying to drag me down. If the wing is FUNCTIONAL then the kit as a whole is POSITIVE, and on the surface I would NEVER want to get rid of it.)

I do this because I have seen SEVERAL inadvertant ditches underwater, including two in the last month, among divers who were either on my boat or on a boat I was diving from. Inadvertant ditches at depth are extremely dangerous, and the thought process that allow a gear configuration in which they are considered "ok" are pure folly. To the maximum extent possible you want to make it extremely difficult to ditch at depth.

I configure my gear to survive, without significant hassle, any single critical gear failure. For this reason I dive either with a buddy or a redundant gas supply sufficient to reach the surface and make any mandatory stops (a largish pony slung as a stage, and I'm putting together a set of doubles.) A buddy who properly manages their gas is sufficient in open water, but not in an overhead (real or virtual.) I weight my kit such that either I can swim up my kit with a total buoyancy failure, or I have two sources of buoyancy, either of which is enough to return me to the surface (if diving dry, the suit can be used in an emergency as a backup source.) This, by the way, is a big part of why I don't like heavy (7 mil, etc) wetsuits - they make that requirement extremely difficult to meet. If I need that much warmth, I dive dry.

I accept that a double failure may kill me, because the configuration steps necessary to manage THAT without undue risk create more problems then they solve.

A 27lb wing is marginal in a drysuit given this philosophy. A 36lb wing is ok, but I do not particularly care for the expando-panel design of the Halcyon product. I had one, dove it for a year, and recently sold it in favor of the Oxycheq. Rather than buy the 30, which would be marginal in my drysuit, I bought the 45. Why? Because unlike with Halcyon there is no drag penalty to the 45 Oxycheq over the 30!

-david

(p.s. - even if you dive with no suit, is your body positive or negative in salt water?)

Positive. But only by a couple pounds. This is grossly insufficient to insure that I can breathe if I find myself on the surface in rough, open water.

 

[Ernesto]

Ok guys. To be totally corrrect, as this seems to be possibly a more complex question than originally thought, I dive with a single steel 98, a 13lb pony is attached to the side of this tank, and I wear a total of 25lbs of lead, but with a 6lb backplate and a 4lb trim weight I'm left with 15lbs of ditchable. So yes my question is if I rip my suit (a laminate suit) wide open, assume it will hold no air, can I safely surface with a 36lb lift BCD where I can then dump my weight belt (15lbs) to remain there?=-)

 

[Genesis]

The single steel 98 is probably -3 or so empty, so your TOTAL suit buoyancy compensation is -28lbs.

You can probably swim up 10-15 lbs, but you won't like doing it. Beyond that you probably CAN'T swim it up. You DEFINITELY can't swim up -28. I've tried to swim up an anchor that is -30 (starting with being neutral at depth) and it was flatly impossible.

If your suit rips, you are -28 PLUS the weight of your gas (about 10lbs if its Nitrox), or -38. That is, for all intents and purposes, you are a brick.

Without ditching a 36 Halcyon is marginal. If you accept ditching your 15lb belt at depth in that situation then the 36 Halcyon is adequate. I consider such a choice to be unacceptable UNLESS I have no other sane gear configuration choice - and I do, so that is not a configuration I would choose.

However, the 45lb Oxycheq is adequate even WITHOUT ditching at depth, and there is no penalty in drag or shape between that and the 30lb Oxycheq wing (I own and have dove both; the 30 is on my "spare" plate right now; my g/f is using it.)

For me, at least, I'd want the Oxycheq 45 or the Halcyon 45, but the Halcyon 45 has the "expando panels" on the outside, and its "teardrop" inflated shape will likely cause trim problems for you. The Oxycheq wing does not have that problem.

 

[Don Burke]

Ernesto once bubbled...
Ok guys. To be totally corrrect, as this seems to be possibly a more complex question than originally thought, I dive with a single steel 98, a 13lb pony is attached to the side of this tank, and I wear a total of 25lbs of lead, but with a 6lb backplate and a 4lb trim weight I'm left with 15lbs of ditchable. So yes my question is if I rip my suit (a laminate suit) wide open, assume it will hold no air, can I safely surface with a 36lb lift BCD where I can then dump my weight belt (15lbs) to remain there?=-)

The 98 will weigh about 6.5 pounds more full than at 500psig.

The 13 will weigh about a pound more full than at 500psig.

That's about 7.5 pounds of gas weight. 25 pounds for loss of suit buoyancy would be a pretty conservative guess. Unless you meet Jack the Ripper down there, I'd expect much less loss. Even if you do, 15-20 would be more realistic.

I think you'll be okay with a 36.

Would it be possible to intentionally flood out the suit in a pool? Rinsing the suit and undergarment once in a while isn't a bad thing anyway. It wouldn't be too hard to figure out a way to measure the force it would take to lift you. A lift bag with a line that runs through a a pulley or big shackle would let you use weights on the bottom of the pool to pull yourself up. That would tell you how much lift you really need before you spend any money. Knowing that the wing had enough lift would really set your mind at ease on your dives.

 

[Ernesto]

I have been thinking about doing a pool flood -- for fun!

And no, in my world ditching weight at depth is an option of U]extreme[/U] last resort. I would rather have a dive plan that sees me cover equipment failures with more sensible options.

ernie