Getting the most bottom time out of the available gear

[tbone1004]

yeah, my sac in the ocean is about 0.4 which is very low, normal people would only have about 25 minutes at depth to surface with 500psi, which is RIGHT on the edge of NDL's with NAUI tables. Any longer than that and you're in mandatory deco, which on the Explorer would suck since you would have to come off of the breather for O2, which is irritating. The real advantage is it's one rig for the day instead of multiple tanks, so instead of having to carry 4 tanks to do 4 dives, you just carry the one unit and call it a day.

 

[RJP]

If depth is not a consideration, then breathing air through a snorkel is the smallest gear that will give the longest bottom time.

 

[rhwestfall]

depth dependent selection... If really shallow, lets throw in a Hookah....

 

[ZzzKing]

A hookah system will not be more cost effective than a snorkel. Even one of those fancy dry ones that the shops try to upsell new divers on.

 

[boulderjohn]

I know there are many options for breathing gas. There are also various systems to breath from. So, what is the smallest gear for the longest bottom time? Air, Nitrox, Trimix, Rebreather, etc?

I am having trouble understanding the question, especially what you mean by "smallest gear." Are you looking for the smallest financial investment to get the longest dives? If so, you need to include the cost of the training with the cost of the gear. For example, you don't just put trimix in your tanks and go diving. The same is true with a rebreather. There is also the issue of the kind of diving you are looking for in terms of length. If you are looking for a longish dive at 250 feet, trimix is a necessity. If you are looking for a longish dive at 90 feet, you would not consider trimix.

 

[swimmer_spe]

Thank you. I love the overall discussion.

I ask this question because I see those videos and pictures of the ridiculous deep dives where the diver has 8+ large tanks strapped to their backs.

Snorkel hands down wins for smallest, but they have a depth constraint.

Nitrox is better for bottom time than compressed air, but it has a depth issue.

Rebreathers/scrubbers seem to be the real answer, but they are super $$$.

So, I guess the answer really is - Depends.
Depends on the depth.
Depends on the cost.
Depends on the training.

Depends on why you are diving.

 

[tbone1004]

nope, answer is always a rebreather.

Snorkel doesn't get you long, but is obviously the smallest
Open Circuit is cheapest/simplest/most idiot proof, but the answer to the smallest size for the longest bottom time is and always will be a proper CCR.

Dive Rite O2ptima for easy reference because they actually list weights.

Pre-dive weight, 51lbs/23kg
AL80 rig avg weight, 42lbs/19kg.

Size wise it is a bit wider, but no thicker, and realistically it's still about the same width as the backplate, so you aren't taking up any more room on the boat. It's good for 4-5 hours, regardless of depth, so at 100ft dives, you are taking up much less room on the boat due to only have the unit and potentially an AL30/40 for offboard bailout vs multiple AL80's or even HP130's for the same bottom time. The number of tanks it saves you is directly proportional to the depth you are diving obviously, but it will always be the smallest rig for the longest duration.

Within open circuit, the answer is always steel tanks over aluminum, and BP/W's over stab jackets. Steel tanks are comparatively smaller and lighter for comparable volume than their aluminum equivalents, AL100's are 8"x26" and weigh 40lbs at 3300psi, but so is a PST E8-130, so you get 30% more gas for the exact same size and weight tank, but you also get to take an extra 4lbs of lead off of your belt.
BP/W gets you a size savings in bulk, and a lead savings due to lack of padding with kydex/aluminum, or a 6lb savings with SS.

 

[The Chairman]

So, I guess the answer really is - Depends.
Depends on the depth.
Depends on the cost.
Depends on the training.

Depends on why you are diving.

Damn! Sounds like RJP's underwear! He tells me they're great for off gassing.

 

[DivemasterDennis]

In the context of recreational diving, nitrox will expand your NDL at a given depth within the limits of the particular mix you are breathing. However, most divers are not limited by the type of gas used so much as their consumption rate. Nitrox offer a longer NDL, and things like proper weighting and trim, not chasing around after stuff, and good buoyancy control will reduce gas consumption rate.
DivemasterDennis