I'm assuming that some sort of basic training is required?? A simple understanding of Boyles Law (pressure-volume relationship) shows that there is the greatest change in volume in the shallows. A full set of lungs at 2m, breath held, would have expanded by 20% by the time you've reached the surface, may be enough to burst the lung. Also, some people have problem in equalising ears in the shallows. A burst ear drum could occur from surface to under the keel.
If you're going to get some training, why not do a basic scuba diving course?
I've never experienced hooka gear so it's wrong to give an opinion. Scuba, on the other hand, is not so difficult. There's a clue to its advantage in its name "self contained".
[QUOTE=Ariadne;3352763]Buy your local diver a beer or two.
Glad you made it to Gambia.
Local diver in Mamaris wants 50 beers (€250).
It's best to dive without smoking drugs
It's impossible to breathe atmospheric pressure air at a depth of 0.5m plus. Regarding embolism risk any air breathed in from any pressurised system at depth will be approximately at the ambient pressure regardless of the fact the air is free flowing or not. There is a quantifiable risk especially as breath holding is instinctive.
If I'd wanted to live in a Banana Republic I'd have gone to South America.
If you're thinking of making your own system, the use of a two-hose mouthpiece (as used on the old honky-tonks - I loved those !) would allow excess air to escape behind you - one reason why some photographers prefer them. Ebay: #260941303223
Providing you stay above 30 feet there'll not be any problems with decompression etc. (assuming you're not diving in a lake at high altitude, or flying the next day), so if all goes pear-shaped, you can simply abandon the gear and go straight up to the surface - whistling as you go, of course.
Another approach would be to buy an out-of-date full-face-mask-respirator as used for firefighting aboard ships, and modify the 2nd stage regulator (built into the mask) for even lower pressure use. I bought a couple at a boot sale many years ago with this in mind, but never did get around to it. The regulator is made of brass etc, so would be suitable for use underwater.
Now although 'body vertical' is an unusual position for snorkelling per se, it's a position scuba divers often present, with their weight belts and tanks etc - and breathing through a snorkel like that is no problem whatsover.
So - if 2 feet is manageable, would 6 feet (which should be enough to clear anyone's prop) ? Worth a swimming-bath experiment with a 'long' snorkel, I'd have thought.
Short while later ...
To answer my own question - Yes, 6 ft would be possible. I've just conducted a quick experiment, by standing on the deck of a boat on the hard, and sucking up water in a tube from ground level. 8 ft was no problem (at which point I ran out of tube), indicating that the lungs can tolerate a negative pressure of 8ft of water without difficulty.
Of course, with a 'long snorkel' you'd need to add a couple of flap valves to ensure you don't inhale your own exhaled breath, either that or discipline yourself to exhale through your nose or the side of your mouth.
Last edited by electrosys; 30-01-12 at 11:10. Reason: after 'quickie' experiment