Actual lift needed?

[Space Beagle]

Hi there,

Hoping someone can help me with my continued education!

Just going through my open water and I've started to look in to buying my own kit. Looks like I'm going with the Zeagle Ranger but I've been contemplating whether it's the stock Ranger or the Scubatoys Brigade. It looks as if the only difference is the wing with the Brigade giving 35 lbs of lift and the Ranger 44 lbs.

I initially thought I needed the extra lift as I'll be diving locally around Vancouver in a drysuit so I'm expecting to have extra weights, hence the lift. Then it struck me (I can be a little slow at times) that the weights are needed so I become neutrally buoyant therefore, if weighted properly, I'm assuming my BC would only need to lift a few pounds to get me back to the surface?

I understand that I become heavier as I descend but why would I need even 35 lbs of lift to get me back to the surface?


Cheers.

 

[cool_hardware52]

Hi there,

Hoping someone can help me with my continued education!

Just going through my open water and I've started to look in to buying my own kit. Looks like I'm going with the Zeagle Ranger but I've been contemplating whether it's the stock Ranger or the Scubatoys Brigade. It looks as if the only difference is the wing with the Brigade giving 35 lbs of lift and the Ranger 44 lbs.

I initially thought I needed the extra lift as I'll be diving locally around Vancouver in a drysuit so I'm expecting to have extra weights, hence the lift. Then it struck me (I can be a little slow at times) that the weights are needed so I become neutrally buoyant therefore, if weighted properly, I'm assuming my BC would only need to lift a few pounds to get me back to the surface?

I understand that I become heavier as I descend but why would I need even 35 lbs of lift to get me back to the surface?


Cheers.

SB,

Any BC needs to meet two criteria; be able to float your rig at the surface if you ditch it, and be able to compensate for the change or potential change in buoyancy of your exposure suit.

You need to calculate the maximum negative buoyancy of your rig with a full cylinder. Just add up the parts, i.e. full tank + reg + can light + any ballast attached to your rig, like integrated weights etc. There are many online sources for tank buoyancy info.

The second requirement, compensate for the change or potential change in buoyancy of your exposure suit requires that you know how buoyant your suit is. Your exposure suit cannot loose more buoyancy than it starts with.

Although very unlikely, a total failure of your drysuit such that it cannot trap any gas could cause it to loose all of it's initial buoyancy. You then would need to replace this lost buoyancy with your wing or BC.

How buoyant is your Drysuit? Put on your undergarment and suit and jump in the water. Vent as much gas as you can at the surface and then add lead until you are just neutral. This will give your the initial buoyancy of your suit.

Which ever is greater, the max negative buoyancy of your rig, or the initial buoyancy of your suit will determine the minimum required BC lift.

Tobin

 

[daniel f aleman]

What Tobin said.

That, and, the questions that you ask should be answered in your open water class. Talk to your instructor...

 

[DiveMaven]

I initially thought I needed the extra lift as I'll be diving locally around Vancouver in a drysuit so I'm expecting to have extra weights, hence the lift. Then it struck me (I can be a little slow at times) that the weights are needed so I become neutrally buoyant therefore, if weighted properly, I'm assuming my BC would only need to lift a few pounds to get me back to the surface?

I understand that I become heavier as I descend but why would I need even 35 lbs of lift to get me back to the surface?

Yikes, remember you don't need lift to get you TO the surface, you want the lift ON the surface to stay afloat. You'll never use the air in your BC to ascend, only to maintain neutral buoyancy during the dive and at the surface.

 

[cool_hardware52]

Yikes, remember you don't need lift to get you TO the surface, you want the lift ON the surface to stay afloat. You'll never use the air in your BC to ascend, only to maintain neutral buoyancy during the dive and at the surface.

This is not entirely true. A normal ascent, with all you gear properly functioning will require venting of the BC and DS, and if you are properly weighted you will arrive at the surface with little gas in either.

OTOH if you have experienced a failure of your dry suit you will either need to drop weight, or have some significant gas in your BC during the ascent. Ditching weight can result in an uncontrolled ascent. That leaves the BC or wing as the safer alternative.

Tobin

 

[Blackwood]

Any BC needs to meet two criteria; be able to float your rig at the surface if you ditch it, and be able to compensate for the change or potential change in buoyancy of your exposure suit.

Good post, but allow me to insert my opinion.

The ability to rescue your buddy is also a consideration. Given a catastrophic loss of buoyancy on his/her part, is your lift sufficient to surface you both? I suppose the worst case scenario is *gasp* warm water diving with no exposure suits (and - for the purposes of this discussion - no lift bags either).

 

[docmartin]

The second requirement, compensate for the change or potential change in buoyancy of your exposure suit requires that you know how buoyant your suit is. Your exposure suit cannot loose more buoyancy than it starts with.

Although very unlikely, a total failure of your drysuit such that it cannot trap any gas could cause it to loose all of it's initial buoyancy. You then would need to replace this lost buoyancy with your wing or BC.
Tobin

doesn't this fail to account for the gas? in the worst case i.e. total loss of suit buoyancy your wing would have to replace this lost buoyancy PLUS the weight of the gas since you are weighted to be neutral with an almost empty tank. I guess this is less of an issue if you have sufficient ditchable weight to make up for the weight of the gas or if you can easily swim up the weight of the gas (not so easy with large doubles).

 

[cool_hardware52]

doesn't this fail to account for the gas? in the worst case i.e. total loss of suit buoyancy your wing would have to replace this lost buoyancy PLUS the weight of the gas since you are weighted to be neutral with an almost empty tank. I guess this is less of an issue if you have sufficient ditchable weight to make up for the weight of the gas or if you can easily swim up the weight of the gas (not so easy with large doubles).

That's a good question. It depends on how you were initially weighted, and what capacity tank(s) you are using, and how buoyant your exposure suit is at the surface.

Let me pose a question: If you are neutral at the surface with minimum gas in your drysuit, no gas in your wing and a full tank what would happen if you swam down to 15 ft without adding gas to your suit or wing?

Tobin

 

[docmartin]

That's a good question. It depends on how you were initially weighted, and what capacity tank(s) you are using, and how buoyant your exposure suit is at the surface.

Let me pose a question: If you are neutral at the surface with minimum gas in your drysuit, no gas in your wing and a full tank what would happen if you swam down to 15 ft without adding gas to your suit or wing?

Tobin

hmmm, is this a trick question? am i being set up? :11:
i'd say that if you are neutral at the surface and you descend without adding gas you will become more negative with every foot that you go down. at some point you'd start dropping pretty fast and remembering all those threads about suit squeeze in all the wrong places...

 

[cool_hardware52]

hmmm, is this a trick question? am i being set up? :11:
i'd say that if you are neutral at the surface and you descend without adding gas you will become more negative with every foot that you go down. at some point you'd start dropping pretty fast and remembering all those threads about suit squeeze in all the wrong places...

No it's not a trick question, and you are correct. As you descend your suit will compress and you will become negative. With the pressure doubling in the first 33 ft you will loose a significant part of the initial buoyancy of your suit by 15 ft.

What's the weight of gas in a typical single cylinder (80-100 cuft) ? No more than 8 lbs. So we can assume that a typical single tank, NDL diver will be about 6-7 lbs lighter at their safety stop. Will a dry suit, or wetsuit that is ~20-25 lbs positive at the surface be 6-7 lbs less positive at 15 ft.?

Tobin