Cold Vs. Warm Water BC

[PugetDiver]

What really is the difference? As you can see I am new to diving. Hey we all have to start somewhere!

I purchased a Mares Jubilee BC Weight Integrated to 30# with Back inflation. I am not interested in hearing negative comments about Mares, however I am interested in knowing if this setup will be sufficient for Cold or Warm water diving? The water in my area stays around 55 degrees all year (Puget Sound) I also do a lot of warm water traveling (Virgin Islands next week! ). The BC has 34 # of lift and I will be diving with a 7mm Semi-Dry Wetsuit in my home area. My Regs are Genesis GS2000, Genesis SKO Octo and an Aeris Atmos computer. Thanks in advance for your advice/comments.

 

[Charlie99]

The BC, Buoyancy Compensator, does exactly that. It compensates for your changes in buoyancy. The two main sources are compression of neoprene wetsuits, and the draining down of air in your tank. The change in weight from air is about 6 pounds for an 80 cubic foot tank. That doesn't change between cold and warm water.

In tropical water you don't have much neoprene, so you don't lose much buoyancy from your wetsuit as you descend. Therefore you don't need as big of lift capability.

If you don't need as much lift, then you don't need as big a bladder. This might reduce drag a bit, although some BCD manufacturers are pretty good about having bellows expansion sort of design that is streamlined when only partially inflated.

Lots of people, including myself, just use one BCD. My Seaquest ProQD ML size also has 34# of lift, and is fine for warm water. One hazard of having excess lift is that if you have a runaway inflation, you will do a better imitation of a polaris missile shooting to the surface. Learn how to and practice quickly unhooking your low-pressure-inflator hose while simultaneously dumping air out of the BCD.

 

[PugetDiver]

Lots of people, including myself, just use one BCD. My Seaquest ProQD ML size also has 34# of lift, and is fine for warm water.

Would you be comfortable using your 34# lift BC with a 7MM wet suit single tank?

I want an all around BC, cold and warm use with back flotation and 30# weight integrated. It also needs to be a great traveler. This is why I chose the Mares Jubilee. I am however a little worried about the lift and don't want to use it until I figure out if it is sufficient.

 

[Brian Gilpin]

PugetDiver

The amount of lead you carry in addition to the type of exposure protection you wear will be the most important determining factors. If you carry 30 lbs of lead then your BC is obviouslsy not enough when you add in the negative buoyancy of your tank (lets say 6 lbs). As you descend your suit compresses and you lose more buoyancy. Steel tanks are more negative so they can add to the weight also.

Add up the weight of your lead, the negative buoyancy of your full tank and any lights or whatever you carry and see if your bc will support them. You may be close so I would suggest you see if your rig with weights will float in a pool. If it works there you should be fine in salt water as well. Hope that helps.

 

[mxracer19]

Why did you buy a BCD without considering these things in the first place?
Im a recent convert of the backplate setup. thought id hate it, I was never more wrong. Maybe you should try one before you use yours...who knows you might be able to return yours

 

[Charlie99]

Would you be comfortable using your 34# lift BC with a 7MM wet suit single tank?

My heaviest suit is an XL size 7/6/5 combo, but I wouldn't have any qualms about using a 7mm with a 34# BCD. You need to look at how much lead + tank negative buoyancy it takes for you to get down. Your BC needs to have enough lift for
1. change in wetsuit buoyancy, plus
2. the weight of air in your tanks, plus
3. any excess lead that you are carrying (in other words, lead weight above and beyond what is needed for neutral buoyancy near the surface with a near empty tank)

How much your wetsuit is going to change buoyancy is a bit hard to tell without actually diving it, but if you go to a pool and find out how much lead it takes to sink it, that will set the upper limit. The only wetsuit I tried to measure lost about 1/2 of its buoyancy at 100'.

If I needed more lift than 34#, then I would be so negative at depth that I wouldn't be comfortable with just a single source of lift. Unless you have a redundant source of lift, such as a drysuit, you should never use so great a combination of lead and negatively buoyant tank such that you couldn't swim back up with a BC that has failed (ripped bladder, corrugated hose hose fell off, valve stuck open, etc.)

The other reason for requiring lots of lift on a BC is so that it will float the tank and lead if you remove it on the surface But if you have a lot of lead, you will probably want to move part of it to a weightbelt anyway. If you have all of your lead in the BC, and none on you, if you remove the BC at depth, it will want to sink while you and the wetsuit will want to head for the surface. Putting some weight on a belt reduces this problem, and it's also a good idea since lots of lead in pockets make them more likely to fall out.

 

[Deano2]

My suggestion is to buy the DUI weight trim system and a standard BC. I use mine in warm and cold water. It's The Best ! No weight on my back and easy entry/exit plus I can load up to 40 lbs/18 kg of weight. The best piece of equipment I have bought to date bar none.

 

[Charlie99]

A similar thread: Is 16kg (35#) lift enough for cold water dives?

 

[PugetDiver]

Charlie & Brian,

Thanks for your comments.



1. I took my BC and filled the weight pockets with the maximum weight 30#. I blew the bladder up manually through the corrugated hose and placed it in my 500-gallon spa. It floated fine, just as I thought.

2. Added 5 pounds of additional weight (= regs, light etc), It still floated.

3. Next I added another 6 pounds (= tank), still floating.

4.Finally added another 2 pounds (just to see) and it sunk.


So it took 43 pounds of lead to sink my 34# lift (rated) BC in fresh water.
To me, it looks like I will be ok in Salt Water. Any reflections?

 

[Minkey]

What really is the difference? As you can see I am new to diving. Hey we all have to start somewhere!

The water in my area stays around 55 degrees all year (Puget Sound) I also do a lot of warm water traveling (Virgin Islands next week! ).

Either you are diving next to a nuclear power plant or my temperature gauge on my dive computer (and also my friend's) is inaccurate, because all my dives have been under 52 F! Have fun diving.

- Another-Novice-Pudget-Sound Diver