JackKit

Jack Ingle is the BSACs Technical Diving Adviser. He is a BSAC National Instructor, an IANTD Technical Instructor, a TDI Tri-mix instructor and co-author of NSAC nitrox courses.
How best to check my nitrox
I have completed a nitrox course and would like to buy my own oxygen analyser. I have seen a few types in dive shops, but which are the best and what features should I be looking for when buying one

Darren Stokes

There are a number of oxygen analysers on the market. If you really want to understand this piece of equipment, get hold of an excellent book written by John Lamb called The Practice of Oxygen Measurement for Divers, published by Best. It really goes into the depths and details of this complicated subject.
I have used various analysers over the years and have always found the simplest models to be the best, especially when using them in the field on expeditions.
The analysers divers use are of the galvanic fuel-cell type. Putting it simply, the fuel cell consumes oxygen and this creates an electric current which is measured as a percentage of oxygen.
Probably the most commonly used analyser is the Vandagraph. I have used this type for many years. It has a separate fuel cell which is attached to the meter and to the cylinder via a plastic T-piece. This ensures that the cell is exposed to the gas being purged from the cylinder and so gives an accurate reading. To this end, make sure the gas flow from the cylinder is as slow as possible.
Another type I have used recently is the Alpha-1, distributed by Sub Aqua Products. This system also uses a fuel cell, but instead of being separate from the meter the oxygen sensor is housed in the meter casing.
It has an adapter that fits into the casing, and a tube with a flow-meter, which attaches to the DIN or A-clamp adapter fixed to the nitrox cylinder.
Both systems have proved to give very accurate readings, but do remember that they rely on the accuracy of the oxygen fuel cell, which does have a finite life and needs replacing after a time. Oxygen analysers can vary in price from £200 to £300.
Handheld or umbilical
I have been looking at torches and would like to know which is best, a lantern-type or an umbilical system

K C Mainwaring

Lets just clear up the differences between these two systems. A lantern is a hand-held torch which has its batteries enclosed in the main body, while the umbilical has a battery that is separate from the lamp-head but linked by an umbilical electrical wire.
Lantern torches are normally quite heavy, especially those with large batteries for longer burntime and a more powerful light. There are some excellent lanterns on the market and we could go on about different manufacturers and models for a long time. However, one that is worth mentioning if you are looking for this type of torch is Kowalski. The company produces an excellent torch which has a good burntime. It comes in various sizes and has a very efficient charging system which does not require breaking any battery seals.
My own preference is for the umbilical system. I stow my battery alongside my cylinders on my back and the umbilical is fed under my right arm to the lamp-head, which is secured to a D-ring on my upper chest area. In this way I have a completely hands-free system whenI am diving and the light is on.
The lamp-head is held by bungee elastic and can be pointed at any object with ease. When I let go of it, the elastic returns it to its original position. Again, there are many makes available but the Metal Sub, which is made in Holland, is a superb torch.
I have also recently used the JMD system and was very impressed with the powerful light it gave.
It also has an adjustable beam, from a flood to a spot, which is achieved by the bulb moving forwards and backwards in the lamp-head.
There is always one downside to good torches - they are expensive.
However, it is well worth investing in a high-quality one, because it can make or break a dive.
In at the deep end
I am interested in participating in a trimix course but there seem to be different course levels and I would like to know what these are.

Gavin Egerton

All the technical training agencies offer trimix courses. I have been a trimix instructor for many years and in the early days there was only one level to teach. However, as trimix has become more popular the training agencies have recognised that there are really two levels.
One is for the entry level (or normoxic trimix) course, and the second is the advanced trimix course.
The entry-level courses are aimed at the diver who wishes to use mixed gas to dive in the 40-60m depth ranges.
At these depths, the amount of oxygen in the trimix is the same as, or very similar to, that of air (21 per cent), hence normoxic.
Helium is added to the mix to reduce narcosis, which makes sense for deep dives. The balance gas is nitrogen.
The advanced trimix course is for divers who want to go deeper. From here on the oxygen level is reduced to avoid oxygen toxicity and the helium level increased to avoid narcosis.
There is a big practical difference in these levels of mixed-gas diving. On deeper dives, equipment requirements become far more punitive, with bigger cylinders required for the bottom, travel and decompression gases.
Deeper than 60m, gas consumption becomes excessive. Planning for these rates plus reserve levels demands that the diver carry these larger cylinders.
More deco is required for these deeper dives, and this also demands the other skills required for such dives.
The course is not only about extra equipment but about understanding the increased potential risk you have to accept with deeper mixed-gas dives.
Make sure you pick your instructor carefully, ensure that he or she is very experienced in mixed-gas diving and, once you have completed the course, I suggest you build on your own depth experience slowly.
How much line
I started to do deco-stop dives (61m on air) a while ago and would like to know how much rope I should have on my primary reel for my SMB

Pekka Kumpula

First, dont use air if you plan to carry out dives in the 60m range. I assume you are diving in tropical waters and I realise the conditions are warmer, with good viz, but nitrogen narcosis can still have a dramatic effect. Sounds like you should be on trimix!
Regarding line on the reel, I tend to carry 30 per cent more than the maximum depth. Be careful sending up line from depth as there is a chance of it snagging. Attach the reel to something solid on the bottom before shooting the bag. Another technique I use is to shoot it from about 20m during the ascent. This requires practice and good buoyancy control.