: Hi Erez. Personally, I wouldn't want to breathe in C02 while under water.
: But, my understanding is: your lungs will not accept C02/they will accept
: Carbon Monoxide... so Monoxide is far more dangerous.

: My first choice by far would be to somehow rig it to let you breath regular
: outside air. Maybe practice in a pool with a longer hose attached to a
: buoy.

Another option: walk your boat out about chest deep, turn it over, dive under and stick your head into the air space trapped in the cockpit. The total volume of trapped air in the empty cockpit will be at least twice as much as what you will have when you are in your boat, but you will be standing up and be able to monitor what is going on with your breathing much more easily. If you don't want to go that far, just put the end of the tubing into the empty space and stay outside the overturned kayak. As you start to deplete oxygen in the inverted cockpit, you will begin to feel a need to hyperventilate (think thin mountain air with a hint of smelly neoprene). That might be the biggest problem since it seems like you would want to control your breathing so you don't breathe in any water that seeps in or drains down the tubing.
I assume that finding a paddling partner to spot you is not an option since that is a lot safer option.

Wes Tanaka