Part 3: Equipment
How to compensate
If you have found you have done all you can reasonably do, but are still frustrated by shorter dives, there are a few options available.
Okay, this is a bit tongue-in-cheek. There is a myth that because Nitrox is air enriched with additional oxygen, you don’t need to breath as much while on it, to get the oxygen you require.
There was a study done, which showed there IS in fact some truth to this. In the realm of 1%.
As in, if you’re getting only 30 minutes out of a tank, you might expect an additional 18 seconds on nitrox.
If you’re looking to use less air, nitrox is not the answer.
If you are cold, your body will be working harder to keep your core temperature up. When your heart rate is up, your metabolism is up, you will be burning more air to fuel this process.
Old, stretched, torn wetsuits do not insulate or retain water very well. Check for a working zipper and holes when getting rental gear.
If you’re getting cold and uncomfortable, first, get a well fitting wetsuit and boots.
Second, start using a full length suit.
Third, consider a hood, or better yet, a vest with integrated hood, which will cover the neck. Fourth, consider gloves.
Please note that many places do not allow the wearing of gloves! (It is against Green Fins policy, as some people who wear gloves tend to touch and damage coral more often). Consider instead going for a thicker wetsuit, or a semi-dry suit, or even a dry suit.
Less neoprene will make it easier to move, which will reduce your air consumption as you work less.
If you have less on your limbs, such as in a “5/3” suit – 5mm on the chest and 3mm on the limbs – then you should find it easier to move around in. Or use a suit with more advanced materials, like super stretch neoprene. Layering can be effective as well. Find what works best for you, based on your comfort and the water you’re diving in.
While this can sometimes be frustrating, physics supports this option. Ensure you have your own dive computer and have perfected your buoyancy, and then stay slightly higher than you would otherwise (unless otherwise directed by your Divemaster).
Remember, at 20m, you use air 50% faster than at 10m (3 atmospheres vs 2 atmospheres).
Bring more air with you
12 liter (11.5L or so for imperial sized) tanks are common and hold about 2400L of compressed air when filled to 200 bar.
Many dive shops stock larger 15L tanks for people just like you! These bigger tanks hold about 3000L of compressed air, and should get you an extra 25% more bottom time. A 30 minute dive becomes almost 40 minutes with the bigger tank, for example.
In most places, a full tank is anywhere between 180 bar and 210 bar. However, yoke systems are usually safe up to 240-250 bar, and DIN systems up to 300 bar. That’s 40% more air, and more bottom time, with no change in equipment!
Some fillers regularly fill to 240-250 bar, which should be no problem, as long as equipment is well maintained and tested. Some of the issue comes from how much longer it takes to fill a tank with that much air.
If you find you need more, just ask the dive shop. Some places which normally fill to 180-200 will have tanks set aside with 220 bar. Or, can specially order / ask for a 240 bar tank. Diving with even 220 can mean the difference between splitting up a group, and being able to get in an hour long dive.
Be aware that this isn’t always for free! Some dive shops will charge extra for this service.
Go sidemount or twin-back mount
If you’re a sidemount diver, two “baby” tanks of 7L will hold 14L of air, and be easier to carry, move around with, and offer an extra 17% of bottom time, or so.
Two normal 12L tanks offer double the time, of course.
Double 15L tanks should be far more than any one recreational diver should need, holding 2.5x as much air as a normal single 12L diver carries.
Go Closed Circuit Rebreather (CCR)
If money and training are no object, check out closed circuit rebreathers (CCR). A rebreather recycles your air, scrubs the carbon dioxide and tops it up with more oxygen.
A normal tank of air so supplied should last at least 3 hours, maybe more.
Plus, there’s the advantage of no bubbles! Just quiet machine humming. The main disadvantages are the cost ($2,500AUD to $15,000AUD), the weight (especially for travel) and the maintenance. Not many dive shops are set up to support CCR either, so call ahead and plan appropriately if you go this route.
It seems like the ideal diver is a tiny, slightly chubby Chinese long-distance female cyclist who is a yoga instructor on the side.
Good luck, and happy bubbles!