mask volume.¿air reserve?

[sebastian]

Its well known the use of the lowest possible volume mask in freediving for saving air in equalizing it.
However, if you use a normal size mask, and when start ascending you suck the air from it, ¿would this small ammount of air help preventing a samba- swb?
I personally dont have too much experience, and I own a normal scuba mask, and this thought is what retains me from buying a real free diving mask.

Any sugestion?

Regards,
Sebastian

[freediver48]

Hi Sebastian,

Part of the answer to your question hinges on the depth that you will be diving in. Deep divers do report getting a small hit from their mask on the way up. The other issues are effort in mask equilization and view. While many of the freedive masks have very low volume, they also have quite restricted view, which if you are doing anything other than performance freediving might be a down side. Personally I would love to replace my mask. It is a moderate volume mask, but it requires quite an effort to equilize it. An alternative is learning to gradually pack more air so that you have more to equilize with, but all things considered you are likely going to find a smaller mask more comfortable, and enjoyable. I hope that this helps.

Best wishes,

Freediver48

[Uli]

Hmm... consider the amount of air in your mask when you are at your greatest depth and are just about to begin your ascent:

A certain amount x has there been before already at the surface,
but another part y you had to "blow" in to equalize the mask.
y depends on the depth:

10 m, y = 1x, 50% of the total amount
20 m, y = 2x, 67% of the total amount
30 m, y = 3x, 75% of the total amount etc.

So at least for the deeper dives, most of the air contained in your mask had to be blown in on your descent. That amount you don't have to do your body good

Of course one could argue that you can get that air back (and at the moment when you need it the most) if you sucked it in on your ascent.

But I would prefer not to have to blow it in in the first place. So if you use a lower volume mask, you keep x small. The calculation above still applies, but as x is smaller, y will also be smaller.

So that was the physics part of the answer.

Now to the physiology part:
Could that air in your mask help to prevent samba or swb?
I honestly don't know. But some people (Kirk Krack, I think, too) prefer to breath out just before reaching the surface exactly for the reason to avoid samba/swb. So the effect of that little oxygen you get by breathing in trough your mask may well be overwhelmed by other effects, that have led Kirk Krack & Co. to breath out.

Regards,
Uli

[Jon]

Actually, Kirk recommended that we try both. Suck the air, or at least try, back in through your nose on the way back up AND start to exhale 10' below the surface on your ascent.
During his clinic there was also a lot of talk about the Aqualung Sphera mask. This mask has a plastic lens wich deforms at depth so you don't need to equalize it as much. I picked one up, but have only been able to play U/W hockey in the pool with it so far. I hope to try it out on some deeper stuff come spring.
Jon

[sebastian]

Hi all!!

I wanted to clarify my question.
I dive for the fun of it, i dont want to break any record, and i like spearfishing too.
My thought about a normal big volume mask is that it may act as a "compensator" in your dives. Yes, it takes more air at the begining, but you dont loose it, you get it back in the ascend.
So if you forget to go up and stay longer than you should, you will have a ¿small -medium-big? chance of not having a swb. I do realize that the actual bottom time will be shorter.
With a low volume mask you will stay longer in the bottom, but if you forget to go up at the right moment you might miss to have saved that bit of air in your mask.

Can any wise and experienced diver say if this make some sense or not?

Regards,
Sebastian

PS, If it makes sense I´m going to buy the biggest volume mask in the market. I think i´ll feel safer at the bottom

[efattah]

I had the same idea about 3 years ago when I started diving. It seemed like a good idea. But, I can say that if you ever do get in trouble (and stay down too long), you may never even know it. Even if you do know it, you probably won't be thinking clearly enough to remember to re-inhale from the mask. For example, when I used to dive with a mask, I would always re-inhale on the way up (even with a low volume mask). However, every single time I ever did a personal best with a mask, I always forgot to re-inhale on the ascent. Why? Because I was too pre-occupied (nervous?) with my current situation, even though re-inhaling was a habit.

So, using a big volume mask will increase your danger, because you won't remember to re-inhale when you are in trouble (if you even realize you are in trouble).

Remember that most dead spearfishermen are found with their weight belts still on. It's the same thing--by the time you realize you're in trouble, you are often not conscious enough to even think about ditching your belt.


Eric Fattah
BC, Canada

[Erik]

Hi Sebastian. I always breath in the air that is in the mask, as soon as I start returning to the surface. It has become a habit over the last 3 years, and I don't have to think about it; even between contractions. I wear a Bandit, which has extremely low volume, for performance attempts, but would not recommend it for rec diving or spearfishing. For that, I prefer a regular, low profile 2 window black silicone mask that you would see in a scuba shop. For diving to 30 metres, I find it just fine, easily doing 2 minute dives in cold water. I have to admit that the amount of air in that mask is noticeable on the way up as I re-inhale it. That air is basically fresh air, and feels good on the way up. With the Bandit, I still inhale, but it is not as gratifying, coming in smaller amounts as it expands.
I think that if you dive to moderate depths with a regular mask, you may be giving yourself a small safety margin : when you feel the urge to breath, it would be earlier than with the small mask, all things being equal. You begin your ascent, and inhale a substantial amount of air, which could make the difference whether you make it or not.
I think a more important factor is the improved vision that you get with a standard 2 window mask or a Cressi Superoccio ( Mares, OMER, Sporasub Samouri, etc). I dove with the Bandit exclusively for most of a whole summer; when I put on a regular mask one day, I was very surprised to actually see a lot more stuff!
Cheers amigo,
Erik Y.

[Erik]

In response to Eric's post, I should clarify that the paramaters I'm describing are during a normal and pleasant dive, with no panic.
I have been able to rebreath the air in my mask during a bad situation, but I think that's because I always do it, and it was automatic.
Cheers,
Erik Y.

[Simon Blampied]

If you are just diving for fun I don't think that volume is that big an issue. You should never really find yourself in a situation where you're pushing your limits the same goes for spearfishing - there's plenty more fish in the sea!!

Personally field of vision is most important - especially when fishing - and I've found that a medium volume mask offers the best option. The lenses are a lot closer to the head and provide greater peripheral vision. I even use it for scuba now as well, and a lot of my friends have converted to conduct their underwater surveys. My favourite is the Sporasub, but there are a lot of variations out there. Oh, and they look pretty cool too!!!

[sebastian]

Hi and thanks everybody that helped solve my question.

As I recreational dive, more view and a small air reserve are more important than longer and deeper dives.
I do realize that in a panic situation I´ll probably not use that reserve, nor ditch my belt either, but in normal conditions it will make my dives a bit safer.

I calculated the volume of my mask (cressi pinova) putted on, and its around 190 cc. lets say 200 to simplify.
So according to my calculations (not very relyable´s), in a 30 mts dive I would have put 900 cc of air in the mask to keep the original 200 cc.
So thats my reserve: 900 cc of precius air, however its not new air, but a bit used, so lets say its equivalent to 700cc of new air.
For a normal person ( 4 lts air, 1:30 total dive) that will be equivalent to 15 seconds in your mask.
If this calculations are right that could be the diference betwen making it to the surface or not.

So I´ll probably buy the cressi big eyes or horizon, have anybody tryed them?

Regards,
Sebastian

[Bill]

If anyone is interested.

A Sphera, Beuchat and Bandit just measured at 86, 89 and 95cc respectively. Is there any numbers for the size of non compressible air spaces in the body?

I ask to check my calculations. If they are correct, contrary to popular opinion, as far as volumes are concerned, you can only dive 2-3 meters deeper without a mask.

Best Wishes
Bill

[crazyfrenchmen]

I do own a Cressi big eye. The mask has a long and soft skirt so it fits very tight on your face. It's also has a very big field of vision with a prolongation toward the bottom so you can see your body more easily. So when you're scuba diving, you can see your equipment, for spearfishing, you see the fish more easily but for pure freediving, i think a smaller one should be better IF it fit's your face well, which is not the case for me.

[sebastian]

Hi Bill,

Just to standarize and know we are talking about the same thing, how you measured the volume of your masks?

I did it filling it with water, and then putting my face in it as in a normal condition. Then I had somebody to check there were no bubles inside, removed it carefully and measured the water that was left inside.
If we both made the same there is an almost 2 to 1 difference betwen a scuba and a freedive mask, thats a lot!

Regards,
Sebastian

[Bill]

Sebastion

Not exactly the same. Face down in the kitchen sink and used a turkey baster to fill it. Dripped dry for a minute, stuck my head in a big empty bowl and measured the contents after removing and dumping the mask. Repeatable and I'm pretty sure it's within 10%.
My thinking has changed. Since you can get the air back, visibility and fit are far more important down to 30 meters unless your losing a lot of air (fit).
I feel that the loss of air and the ease of equalizing with a nose plug are the main factors in the abilitie to dive deeper without a mask. I also have a couple of good stories when I tried to spear fish with a bandit but, they're not for free. It'll cost you a beer when you get to Kona.

Best wishes
Bill

[freediver48]

Hi Bill,

Just out of curiosity, what Beauchat did you measure? I have one of the Primos, which were new this year, and I like it just fine for scuba, but it is up for replacement for freediveing.

Thanks,

Doug Morgan,
Lantzville, B.C.