Tuesday, May 25, 2010

RIY Banks and Exhale dive video clip

We went out to the RIY banks on Saturday. Some motor issues - spluttering and dying of one motor. On investigation a pinched fuel line was the cause of the problem. Check that a fuel drum is not pinching a fuel line shut - especially before surf launching.
The vis was a splendid 20-25 m and a comfortable 18-19 deg C. Tail showed up soon after we got in and then seemed to vacate the banks for all practical purposes. Between 4 of us we only got 4 fish. I managed a big bonito of 4.5 kg (made good sushimi last night). I believe it was a personal best for me - I can't remember shooting a bigger one.

The deeper water was a little cooler - perhaps 17-18 deg and a bit misty but there was also not much action.

I eventually quit the spearfishing an began doing exhale dives to amuse myself. I managed about 7 m on about 95% exhale. It feels weird to surface and then inhale instead of exhale. If a nice tail came in at that time I would have had to leave it unless it gave a totally easy "point and shoot" chance. I could not descend not waste energy lest I black out and sink.
I even took a clip.

Caution: Doing exhale dives is entering a whole new game - laws change as you are running under different systems. Its like comparing fixed wing flight to flying a chopper. It can be dangerous to uneducated persons. IT COULD KILL YOU IF YOU MESS IT UP.

What's different?:
1. You have lost perhaps 75 or more of the life sustaining oxygen you normally have. Logic tells me exertion must be at least 75% less than in a full inhalation.
2. Pressure has a big effect, FAST. You would normally reach equivalent compression of your lungs and surrounding organs (including you blood pump - heart) at say 40-50 m. If the compression is fast and you are not used to it you can suffer a number of damages including rupture of your lung, excessive squeezing on your heart, pain and extreme physical discomfort. You will not be able to equalize either and can even rupture ear drums or blood vessels in your eyes.
3. chances of blackout increase with increased chances of water entering your lungs.

I would never practice such exhale dives during a big sea near pinnacles where water can push you up or down as is surges over pinnacles. RIY banks is just such a place - I have been pushed down to 18 m from 10 m when diving next to a pinnacle that drops from 8-20 m vertically. Imagine having exhaled and reaching 7 m and you cannot descend further due to not being able to equalize and having moderate pain on your organs due to the pressure and the exhale. Now a surge pushes you down to 14 m in 3-4 seconds - that's a recipe for disaster - even if there is a competent diver watching your every move.

The advantages are:
1.That you simulate deep dives in shallow water and you can kick in your mammalian dive reflex much faster. What happens is that your spleen is squeezed and may raise your ability to carry oxygen by the release of red blood cells rich in haemoglobin.
2. The sensations experienced are similar to those at 40-50m on a normal inhalation - it can make for good equalization practice and an easier way to try techniques such as mouth fill equalization.


Here is the clip - I filmed myself. Note that I do not put much effort into the dive and my rather low buoyancy keeps me in equilibrium at 6-7 m

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