In the prone position, the gas in the lungs(chest mounted) is at a slighty higher pressure.. Most divers agree its easier to exhale into higher pressure than inhale from a lower pressure to a higher pressure. On chest mounted lungs you have gas below you, and some above (the canister,hoses) this seems to be a good balance, the positioning of the "t"s which the hose connects to is very important (normally the ts are at approximate lung centroid) as is the counter lung positioning.. if the lungs are not firmly attached to ones chest and you go in the surpine position the inhalation resistance becomes noticable trying to breathe against lungs just a few cms above your chest.
On back mounted counter lungs bag placement is critical. If I remember correctly the max recommended distance is 11cm from lung centroid.. I haven't dove a back mounteed CCR (I'll own one shortly) but my guess is that in the prone position the buoyancy change would be even more noticable..
A book I would recommend is
Life Support Systems Design
Diving and Hyperbaric applications
By M.L. nuckols/ W.c. tucker and A.j. sarich
I believe its available from best publishing.
This is a great text for those with a mathematical and scientific background, for other most of the material will probably be uncomprehendable.
In the prone position(front mounted) the buoyancy change is less noticable than when head up since the gas will now be at the highest points (a reasonable amount above the lung centroid)possible therfore the largest volume displacement.
I'm not sure how to figure out what the buoyancy change in reality is but Its probably about .5kg or less (from perception.. I could be totally wrong) Its definately more pronounced in shallower water where our bodies are less compressed, but somewone who is really paying attention and is truely "neutral" you can see the effect.
Rebreathers without an auto diluent addition valve don't vent large amounts of gas when the hose is above the head or make you look like a chipmunk when in less than optimum a position (with an auto diluent valve it will act like an old 2 hose reg since it will constant add gas as long as the pressure at the ADV is less than ambient)
On back mounted counter lungs bag placement is critical. If I remember correctly the max recommended distance is 11cm from lung centroid.. I haven't dove a back mounteed CCR (I'll own one shortly) but my guess is that in the prone position the buoyancy change would be even more noticable..
A book I would recommend is
Life Support Systems Design
Diving and Hyperbaric applications
By M.L. nuckols/ W.c. tucker and A.j. sarich
I believe its available from best publishing.
This is a great text for those with a mathematical and scientific background, for other most of the material will probably be uncomprehendable.
In the prone position(front mounted) the buoyancy change is less noticable than when head up since the gas will now be at the highest points (a reasonable amount above the lung centroid)possible therfore the largest volume displacement.
I'm not sure how to figure out what the buoyancy change in reality is but Its probably about .5kg or less (from perception.. I could be totally wrong) Its definately more pronounced in shallower water where our bodies are less compressed, but somewone who is really paying attention and is truely "neutral" you can see the effect.
Rebreathers without an auto diluent addition valve don't vent large amounts of gas when the hose is above the head or make you look like a chipmunk when in less than optimum a position (with an auto diluent valve it will act like an old 2 hose reg since it will constant add gas as long as the pressure at the ADV is less than ambient)