BC Lift Question

[danvolker]

I have had a seal let go in my drysuit, allowing so much water in that on getting out of the water, my legs were completely full of water--so heavy it was really hard to walk
But underwater, even with my 18 pound lift wing, I had no problem getting positive. At normal insulation levels with a steel hp 100, I need no weight belt, and need only a tiny bit of air in the wing at the inception of the dive to be neutral. With the big flooding, maybe I half inflated the wing ....
People that need huge amounts of weight with the drysuit should probably have some of it as ditchable, rather than wearing a virtual life raft as a bc

 

[turnerjd]

Wow! what sort of drysuit and undergarments do you have? I have never come across a single person that didn't need weight when diving dry. What is a HP 100 in metric? a 232bar steel 10L or 12L tank?

However, for your configuration, you BD/Wing is good for your setup, and I only wish I could dive with less weight.

Jon

 

[danvolker]

Wow! what sort of drysuit and undergarments do you have? I have never come across a single person that didn't need weight when diving dry. What is a HP 100 in metric? a 232bar steel 10L or 12L tank?

However, for your configuration, you BD/Wing is good for your setup, and I only wish I could dive with less weight.

Jon

Dont know the conversion off hand, but these are very heavy single tanks..and great for Drysuits!!! ..If I dive with a skin on instead, and an hp 100 , my 18 pound wing requires almost 98% of full inflation to acheive neutral...far from ideal....fortunately, if I have to use them with a skin or 2.5 mm suit, the profile of an 18pound lift halcyon wing is so low, even fully inflated it is low drag compared to most much larger BC's or wings..and with my DiveR freedive fins, I can swim the typical anchor ( for up to 50 foot boats) off the bottom without any bc assist--meaning I am not really concerned about redundant bouyancy with my configuration. If I could not swim this up easily, I would be concerned.

 

[modzs]

Being able to swim your rig up is the best form of redundant bouyancy in my book.

 

[Hatul]

@Hatul: DevonDiver is discussing the concept of a "balanced rig." Although that's good information, it's not what I was referring to in the post you quoted.

Let me see if I can explain my statement a little more clearly...

We know that a BCD/wing needs to have enough lift to float the rig by itself (without the diver) at the surface.

For several of the drysuit divers I know, their shell drysuit + heavy undergarment configuration has approx. 26 lbs. of positive buoyancy. With a HP100 tank (-2 lbs. empty), SS BP (-6 lbs.), and reg (-2 lbs.), this means that the diver is probably carrying about 16 lbs. of lead. If the diver attached 100% of that lead to his rig (using trim weight pockets or those snazzy Halcyon/Apeks/GolemGear waist strap-mounted weight pockets), his wing would need to provide at the beginning of the dive with a full tank: 16 lbs. (lead) + 6 lbs. (SS BP) + 2 lbs. (reg) + 10 lbs. (full HP100 tank) = 34 lbs. of lift.

How about this idea for dealing with the rare event of a drysuit flooding. Instead of taking a huge wing to deal with that rare event, just be prepared to dump enough weight to account for the loss of buoyancy from the drysuit flooding. You'd have to figure out before hand what that loss is in lbs/kg and just be prepared to drop that much. For example in my Zeagle BC I can open up the weight pockets and dump one or two weights from there without pulling the ripcord to dump everything.

I'm not sure how to figure out the buoyancy loss from drysuit flooding, but in the worst case you can purposely flood the suit in a pool and see what your buoyancy change is. The salt water buoyancy will be slightly greater than for pool water (2.5%).

Adam

 

[DevonDiver]

I'm not sure how to figure out the buoyancy loss from drysuit flooding, but in the worst case you can purposely flood the suit in a pool and see what your buoyancy change is. The salt water buoyancy will be slightly greater than for pool water (2.5%).

Or..... alternatively..... just get in the pool wearing shorts and a rash guard.... work out your weighting with those.... and subtract the difference from what you need with a wetsuit...

 

[turnerjd]

How about this idea for dealing with the rare event of a drysuit flooding. Instead of taking a huge wing to deal with that rare event, just be prepared to dump enough weight to account for the loss of buoyancy from the drysuit flooding. You'd have to figure out before hand what that loss is in lbs/kg and just be prepared to drop that much. For example in my Zeagle BC I can open up the weight pockets and dump one or two weights from there without pulling the ripcord to dump everything.

I'm not sure how to figure out the buoyancy loss from drysuit flooding, but in the worst case you can purposely flood the suit in a pool and see what your buoyancy change is. The salt water buoyancy will be slightly greater than for pool water (2.5%).

Adam

Not a bad idea for those diving with a weight integrated BC (even if I don't)

to work out the weight you would have to lose, just get in the water with suit+undersuit and nothing else. Find the weight needed to be neutral like this, and Rob is your mothers brother.

Jon

 

[DivemasterDennis]

Call me simplistic, but I think you all are really overthinking this thing. I think we can distill down why someone would want greater lift in a bcd than "normal.

1) you are an instructor carrying excess weight in case a student needs it, drops some of theirs, etc.
2) you are diving in conditions that can present strong downward current and you want the lift for emergency response if needed
3) you need it to compensate for the negative buoyancy of what you are carrying, which might be equipment on a tech dive, something you catch or kill while diving, or a lump of gold or silver you find on your treasure hunt
I wear a high lift capacity BCD on training weekends at the local reservoir because I am carrying and planting and retrieving platforms, navigation lines , and such stuff, which is negative, and also because I carry extra lead for students who might need it as the swim out to the platforms is over 100 meters. AT other times, when diving for my own pleasure, in warm water, I am a minimalist and wear the least heavy and bulky bcd possible and the lowest weight possible.
DivemasterDennis

 

[aquaregia]

1) you are an instructor carrying excess weight in case a student needs it, drops some of theirs, etc.

How much spare weight do you carry? Five pounds? Twenty pounds? We use a float for training dives. Something is required to raise an ascent line, and a float is something to hold onto at the surface and storage for lead.

2) you are diving in conditions that can present strong downward current and you want the lift for emergency response if needed

I can't speak to this, having never dove in it. The idea of being massively buoyant to get out of a downcurrent scares me, but so do most things about downcurrents. How quickly can you vent a 94# OMS wing once you manage your way out (honest question)?

3) you need it to compensate for the negative buoyancy of what you are carrying, which might be equipment on a tech dive, something you catch or kill while diving, or a lump of gold or silver you find on your treasure hunt

Even if you need no weight, or are negative, even the smallest wing gives you 18# of lift. I haven't seen a doubles wing under 38#. You're carrying *that* much gear? There's no way I'd dive with the potential to be 40# negative if there was any other way, including Clorox bottles or wearing more socks.

I use lift bags for lifting things. They can't embolize.

 

[flots am]

1) you are an instructor carrying excess weight in case a student needs it, drops some of theirs, etc.
2) you are diving in conditions that can present strong downward current and you want the lift for emergency response if needed
3) you need it to compensate for the negative buoyancy of what you are carrying, which might be equipment on a tech dive, something you catch or kill while diving, or a lump of gold or silver you find on your treasure hunt

4) It's nice to be able to come up under a panicing diver and give them some altitude while you figure out and deal with whatever their problem is. Getting a diver's head significantly out of the water calms them down quickly.

Some people advocate "just enough" buoyancy in a BC. I'm not one of them. I dive an XL ScubaPro Classic+, which IIRC, has around 75Lbs lift. "Extra drag" is irrlevant to me, since I never move that fast anyway and I've never had a problem venting a properly designed BC.

flots.