[NotDeadYet]

You dive within the limits of your scrubber. If you have a four hour scrubber then you do a 4hr max dive. If you want to do longer then increase your scrubber capacity... easiest way would be to buy a bigger rebreather.

I plan for 4hrs max on the scrubber: I allow 3hrs dive time + 1hr "fuck me!!!" time. The scrubber is rated for three hours though I think this is more to do with a conservative liability ass covering rating, it's done four and in an emergency I think it will do longer, especially if you go semi-closed with offboard gas. If I'm in this situation (which would imply something has gone badly wrong somewhere) then I've gone beyond "fuck me" and probably strayed into "stupid c**t" territory. Regardless, I always carry more than enough OC gas to get me out from wherever I plan to go. The rebreather to me is like a penetration stage: dive on halfs but with a little bit of padding as there is plenty of excess OC gas around to get out on.

On a lot of dives, deco time forms a huge chunk of your dive time. Normally I've been doing the whole dive on one rebreather but I have another with a 90min scrubber which is for O2 deco use (but quite probably will get converted to CCR so I can do the whole deco on it).

An alternative would be to do deco on OC. If it wasn't for the logistical aspect then I would be quite tempted to do that and save the RB purely for penetration and then emergency use (once I've reached deco). I'm not a fan of constant high pO2's during deco, I've gotten quite wheezy after a few long dives. But given the logistics, a second decobreather is a more appealing prospect.

As for dive planning, I plan according to what bail out I have. If my bailout allows a 40min penetration then I do that regardless of what the scrubber may handle in excess of that. In the water, my turn point is either this penetration limit or 1/3 of diluent, whichever comes sooner. In caves you do use a considerable amount of dil as opposed to open water. For me, availability of diluent is THE major controlling factor. I don't worry about oxygen, I don't even have a gauge on it. A lot of people will disagree with that but I don't see the point. I gauge it before I get in the water, I know what the usage rate will be and anything that will affect that will be VERY evident underwater. You can stay on the loop without oxygen in a cave but you can't get very far without diluent.

I have an offboard connection for diluent to my manifold. Other than that my KISS is a stock unit. It has no mods and no HUD. The article on RBW says this is an essential, I would rate it more a luxury. I dived hogarthian when I was OC, my attitude towards fancy bits of kit was always "if it isn't there then it can't fail and it's one less broken bit of kit to deal with".

Ramble... ramble... ramble...

I would also add that I start off planning my dive as an OC diver. I only go CCR if it will make the dive easier or safer.

And another thing, the above is probably a load of bollocks as I am neither open water nor cave CCR trained.