Fresh water vs salt water

[DivingDane]

Hi guys, I have started training constant weight in a fresh water lake for the last couple of months. the question is:

Is there a difference in pressure between fresh and salt water at a given depth?

the reason i ask is that it seems i can equalize easier (therefore deeper) in fresh water compared to salt. i dont feel as much pressure on my body. is this to do with the salinity or am i just imagining it.

DD

 

[vali]

the salty waters are havier than the fresh waters
this could be a reason?

 

[DivingDane]

i understand that salt water is heavier than fresh, hence the reason we need mre weight to overcome the increased bouancy, what i am curious about is if this increase in weight i think its only about 5% or less??? has an effect on the pressure exerted on the body at depth (for arguements sake 30m).

 

[xstephenx]

I think it is in your head. Salt water has a specific gravity of 1.025 vs. 1.000 for fresh water. P = den*gravity*height, so pressure is linearly proportional to density. You would only notice a 2.5% difference in pressure going between salt and fresh water. I would imagine you wouldn't be able to tell the difference.

 

[DivingDane]

excellent so its just me getting better and focusing more when i am in the lake woohoo! i was worried it didnt really count when in fresh water. thats good going back to the lake again tomorrow. MUST GO DEEPER!!!!!!!

(there is a group of divers and we have a friend who enjoys being on SCUBA at 40m so no i'm not doing this by myself)

 

[vali]

how deep did u dive in fresh water? [your PB]

 

[apneaboy]

Many computers measure salt water density and do not take into account you are diving in a fresh water lake/quarry so will actually measure slightly shallow in fresh water as they measure pressure not actual depth as salt water is denser.

Depending on the computer setting the difference is closer to 3% so that if you dive in fresh water to 30m for instance you have actually done 31m of depth. 60m would be 62 metres of actual depth etc etc.

It does make a difference. Every little helps

 

[DivingDane]

Well had a crap day yesterday, EQ just didnt want to play the game, not to mention the vis was terrible at 25m it was pitch black could not even see your hand infront of your face, honest! so yeah 25m was as far as i could get (with bottom time) just couldnt equalize any further.... but so far PB is only 31.6m but hopefully that will be fastly improved on in the next couple of months.

DD

 

[Erik]

Just a guess, but it sounds like it's time to learn the mouthfill?
Cheers,
Erik

 

[DivingDane]

Mouthfill technique already!!!! surely not i've got a fair few friends which are diving significantly deeper than i am and i'm pretty sure they dont use mouth fill, i thought this was only for deeper dives? i figured i'd work on my long and thorax flexibility so that i have more useable air touse during EQ, then again i'm using Frenzel so i quess mouth fill is the next step just thought i wouldnt have to worry about it until i started diving deep????

When do most divers start to use mouthfill technique... 35m 40m etc???

 

[Erik]

I couldn't get past 25 metres without a mouthfill. I can now, but I don't see the point as the mouthfill is painless and stress-free!
I just think that when it gets to the point where you're struggling to get air to equalise, then use the easier path.
Cheers,
Erik

 

[jay cluskey]

mouth fill is the way forward
you will be at residual volume at about 30m hence , difficulties at 25 m
dive safe and dive with a fellow freediver not a scuba diver be careful bud

 

[DivingDane]

ah Jay sorry prob didnt explain myself properly, there are always at least 3 of us training (if not more) which are freediving but we also have a friend who enjoys sitting at the bottom on SCUBA so we have both forms of safety and also train with set line and lanyard (very comforting in bad vis).

so with mouth fill do i still dom frenzel the same way as usual just fill my mouth with air a little earlier and hold it there for EQing with?

thanks guys

DD

 

[fflupo]

yes, once you filled your mouth you need to keep epiglottis closed and fulfill a frenzel or btv ..

you can train this in shallow water with exhale/frc dives

gravity sucks

 

[Erik]

Try a mouthfill at the surface before you dive, then take it as deep as it will go. It's a good way to practice equalising.
If I dive to 30 metres, I will mouthfill at 20, which is relatively easy and stress-free, then glide down to 30 (with speargun).
Cheers!

 

[DivingDane]

Sweet i'll give it a try next time i'm up at the lake, and may just start practising this on FRC dives to 10-15m to get the hang of it.

DD