Being able to fill your own tanks is a benefit in remote areas, and allows you to dive wherever you are. Be warned though, small compressors are hellishly noisy.

SCUBA diving was always one of the things we wanted to be set up for when we cruised because we wanted to dive in more remote areas where we it would be hard to get tanks filled. And it has proved to be the case, as we have been able to dive in places such as the atolls in the Tuamoto chain and the eastern islands of Indonesia. Our experience is that it was well worth the expense of equipping the boat for independent diving.

However before you decide how much equipment to buy consider your intended cruising area. For example if you only plan to cruise in the Caribbean it is probably not worth the cost of carrying a compressor as tank fills are cheap and easy to obtain. Increasingly marine parks are being created that prohibit independent diving so you do not need your own tanks as you have to go with a dive store. Also, we sometimes use dive stores where they are available particularly to do difficult offshore or drift dives.

If you plan to cruise the Pacific or Southeast Asia (especially the more remote areas), then carrying a compressor is a must if you want to dive regularly.

There are a lot of issues raised in this question so we've tried to cover them under the subheadings below. But if that makes it seem daunting, don't be deterred. There is nothing like diving where you know no one has ever dived before, to see reefs that are truly pristine, to dive with sharks that are not trained to be fed like monkeys in a zoo, and to dive without a group of 12 other divers stirring up the sediment and frightening the fish; the rewards outweigh the costs by several orders of magnitude.

DIVING INDEPENDENTLY
Training/skill level

We were both PADI advanced divers before we started cruising. Because we knew we would be diving without the backup of a dive store we took the rescue diver course. This made us realize how much more there was to safe diving when you have to take full responsibility, so we also took a Divemaster course. (We eventually took the instructor exams too but it adds little to your diving skills as the focus is on teaching methods and student supervision. However it means we can safely take friends on introductory dives when they come to stay with us.)

It is true to say that the more we learned about diving the safer we felt. At the very least we'd recommend training as far as rescue diver as it will greatly increase the chances of saving your buddy's life if something goes wrong. Your actions in the first minutes of a problem can significantly affect the outcome.

Drift Diving

Some of the best diving is in coral reef passes, which necessitates doing a drift dive. Although we try to do these at slack water, it is not uncommon to find that although the current is slack on the surface it is still running fiercely at depth, so we always use a surface marker buoy while someone follows in the dinghy.

Trying to follow someone's bubbles is not a good idea in anything other than the most sheltered and calm conditions. We dived through one pass and traveled a mile and our friends doing top cover in the dinghy would never have been able to follow our progress without a surface marker buoy-while we were merely drifting they were motoring quite fast to keep up with the buoy and the surface turbulence made the bubbles impossible to see. Ideally we use other divers to do top cover then we swap around and provide cover for them, but if that's not an option we have also used local boat boys. But make sure the deal is clear, if they are waiting at the buoy when you ascend they'll get a bonus, otherwise you may find your top cover has gone off fishing somewhere.

SAFETY

Everyone needs to work out what feels safe for them but for those who have only ever dived with a dive store or somewhere well monitored like the BVIs we've listed a few of our personal safety precautions.

When diving independently we always put a spare tank in the dinghy, and carry water, a first aid kit and hand-held VHF. We also use a "Diver down" flag.

We dive on computers, but never push the tables and dive very conservatively. We always return with plenty of air and do safety stops. With a compressor we can do a dive as many times as we want so we'd rather do a good dive again than try to squeeze every last second out of one dive. The habit of trying to empty the dive store's tank needs to be avoided. We never dive alone, i.e. without a buddy. If there are no friends around to do top cover we dive where we can anchor or tie the dinghy to an underwater rock.

DAN oxygen kit: obviously optional. It is expensive to buy, big to store, and needs to be inspected periodically, but it could save your life. We feel it's like our life raft, we consider it a good investment even though we hope never to use it. You need to take the DAN Oxygen course.

In areas where there are sharks (the whole of the Pacific for example) we do not dive if people are spear fishing.

UNDERWATER WORKING

Most of the time, we scrub the bottom using a snorkel and free diving. This is aided by using a suction device (we use a propriety type, but any sort of plumbing plunger would do) to hold us to the hull--otherwise you go back and forwards rather than the scraper. We also use a stainless plasterboard knife, which is normally used to plaster the gaps between sheets of plasterboard. Ours is the widest scraper we could find (14 inches), which speeds up the job dramatically.

For any sort of underwater work such as changing anodes, we use full dive gear.

A tip for when you have to clear ropes and nets off the propeller, for it will happen sometime! Use a safety line to a fender out of the back of the boat, as it is surprising how fast the boat moves in zero wind. Brian had a major shock in the North Atlantic when he went in to clear a net. Although the log registered zero, the boat drifted off after he had jumped in. With full dive gear on it is not possible to move very fast on the surface, but panic helps!

EQUIPMENT

If you dive with a dive store they will supply equipment of varying quality depending where you are in the world so lots of cruiser divers prefer to use their own gear. Dive stores will usually offer you a discount if you have your own equipment.

Tanks

Because you are filling your own tanks it is easy to become sloppy about maintenance. If you do not have your tanks regularly tested you will not be able to get them filled at dive stores. French islands have much more stringent requirements and will often refuse to fill tanks that do not have French certificates.

Corrosion is a big problem; we have had to scrap several tanks because of corrosion around the valve o-ring, we now keep that well greased. Dive stores that do inspections would not normally do this, so if you get the tanks inspected, remove the valve yourself and grease the O-ring and the surrounding area. Ideally use a corrosion sealant like Duralac between the top of the tank and the valve.

Use unpainted aluminum tanks and do not store them in tank boots. We have had the paint sand blasted off all our tanks so we can keep an eye on them. Tank boots retain water, which causes corrosion.

If you can afford the fresh water to dunk the tanks after each dive, so much the better, but as a minimum flush your regulators and BCD if you want it to last more than a year.

Compressors

When we were planning our equipment we looked at AC driven compressors, but found that they needed a huge genset to run them, because of the starting loads, which are several times the running loads. If you plan to use an AC compressor, trial run it to make sure your generator can handle it.

Instead we bought a stand-alone portable Bauer diesel compressor, choosing diesel as it seemed safer than petrol (gasoline). However the dirt and noise caused us to change the motor to petrol when we had it overhauled recently. It will pump a normal sized tank from empty in 30 minutes, but if you retain some air in the tank, as you should, then normally we plan on about 20-25 minutes per tank.

Because of our set-up we have had no experience of the floating snorkel-type compressors but others we know who have them use them successfully for bottom scrubbing etc.

Our diving knowledge makes us wary of them, as it is possible to stay down at depths and times that exceed the tables. More importantly, there is the risk of a held-lung ascent in the event of an equipment problem with the associated dangers of lung expansion injuries. So we wouldn't recommend them for general diving, but for hull work, they are obviously ideal.

BOOK PLUG

We couldn't resist mentioning that while we were in the Caribbean we wrote three diving guides for the Eastern Caribbean islands (Puerto Rico to Tobago). You can see these on our website www.caribdiveguide.com