Does water get inside your BCD?

[johm77]

I hear you have to rinse out the inside of your BCD.

So I'm wondering. How much sea water actually gets inside the BCD? If it's a significant amount, couldn't that be dangerous?

 

[CApenguin88]

its not that much that could be dangerous but its always a good idea to get that saltwater out and rinse it.

 

[Charlie99]

Water inside your BCD doesn't affect buoyancy. Imagine taking a couple of gallon milk jugs of water with you scuba diving. They are clumsy and have drag, but they are the same density as the water around you and don't affect buoyancy.

The water in a bcd adds a tiny bit of drag. It also takes up some of the bladder space, thereby reducing the capcity of the bladder or wing. If for some reason you needed that buoyancy you can force the water out by putting in a whole bunch of air and then opening a dump valve at the lowest point on the BCD. It's hard to think of a situation where you'd have to do this.

The water typically gets into your BCD when you have a near empty BCD and continue to try and dump out the non-existant air. Not a big deal. Don't sweat it.


Charlie Allen

 

[spectrum]

Charlie99 gave a good explanation.

It will vary with experience from nil to over a quart per dive.

This is why it's very important to clean your BC inside and out after each dive day.

This should have been covered in you OW class even if it may not be in the actual agency curriculum.

Pete

 

[drbill]

I agree with Spectrum. Common to have this happen during a dive. Simply use the dump valve to eliminate it during the surface interval and rinse your BCD out with freshwater after your day/trip is over before storing it.

 

[pickens_46929]

Water inside your BCD *does* affect bouyancy in two ways... but if it's a just a little bit there's nothing to worry about...

1) Since it's the same weight as the water, you loose displacement and therefore bouyancy... if it didn't matter, a BCD wouldn't need to hold any air for you to control your bouyancy. While a small amount won't have a *major* affect on your bouyancy, a BCD that won't hold air or otherwise inflate isn't going to do anything for you.

2) Since water is denser (heavier) than air, it'll go to the bottom of your BC. If it is a significant amount (eg. 2# of water), then your trim will be affected and you might have a hard time staying horizontal, level or whatever position you're trying to maintain. Basically you have 2 extra lbs that you're trying to hold in a position it doesn't want to be held at...

As for what it means and what to do about it... if it's a lot of water, and you have problems with bouyancy (eg. constantly added air or letting air out even at depth) it can mean you have too much weight in your weight belt...

What to do about it... drain it as best you can after you dive, right there at beach or boat... if you're going to dive within the next day or so, you don't need to do anything beyond that... if you're done for the week or whatever, then rinse the inside out... add a good bit of water... stick the inflator up to a hose or faucet... add a gallon or so... swish it around... drain it... repeat until it's not salty... yes, taste the water draining out... if you couldn't drink it... it's not clean yet... when it's fresh water again... drain the best you can... inflate... leave sitting so the lowest part is your inflator... then drain again in the morning after all the water collects at bottom overnite...

Big reason you do the rinse thing is because of the salt crystal forming and cutting the bladder inside the BCD... oh and last thing is be careful of heavily clorinated water like pools... it's not quite as bad as salt water (eg. crystals) but it's not like fresh fresh water either... if you do pool diving... think about using a BCD conditioner every so often.

Dave

 

[Charlie99]

Dave -- you should put a bunch of water in your BCD and try diving. You will probably find that your experience doesn't match up with your post. I'm not trying to pick on you, but what you post doesn't match up with either my personal experience or what the physics of the situation tell me should be happening.

As you change positions with some air in the BCD but no water, the air bubble always goes to the highest point. Same thing happens if you have a few quarts of water in the BCD. No effect on trim. Try it if you don't believe me. I have tried it.
While at first glance it seems that 2# of water will effect your trim, it is moving both your center of mass and your center of buoyancy equally, and has no effect. Think about my milk jug analogy. It doesn't matter where you tie them onto your body -- they won't affect your trim if they are filled with the same water that you are diving in.

I have found that being underweighted is more likely to lead to excessive water in the BCD than will being overweighted. An overweighted diver always has air in his BCD and is less likely to get water into it. I have trouble with water in the BCD when I'm a bit underweighted and keep trying to dump air when there isn't any.

Yes, 2# of water in the BCD means that your max buoyancy will be 2# less, IF you retain the water in the BCD when your overpressure dump valve pops. As I noted, having a full to bursting BCD is a rather unusual case, and even then all you have to do is to open the lowest dump and the water will be forced out as you continue to fill the BCD.