One of the biggest kit changes that most divers make is the move from a single cylinder to a twinset. The vast majority of divers use a traditional single cylinder rather than a twinset and in order to justify the additional cost and the extra weight this configuration obviously has to provide a significant advantage over a conventional setup. A twinset provides two primary advantages over a single cylinder setup. The first is the increase in gas volumes and the second is the increase in redundancy. There are other ways to achieve the same advantages. For example increased gas volumes can be achieved by using a larger cylinder but this doesn’t provide increased redundancy. Increased redundancy can be achieved by use of a pony cylinder but this doesn’t provide any additional usable gas volume. Only a twinset will provide the balance of increased gas volumes and redundancy. Twinset diving doesn’t necessarily have to mean using a backplate and wing. There are plenty of divers who use a twinset with a standard jacket style BCD. The Buddy Commando, that standard of the UK club diving scene, can easily be used for twinset diving. However the majority of twinset divers eventually migrate to a backplate and wing configuration. This type of setup has a number of advantages. A wing provides buoyancy in the same location as the twinset and so is more effective at counteracting the weight of the twinset. Having the buoyancy behind the diver but next to the twinset helps to support the weight of the twinset and lifts the twinset off the divers back. All of this means that a wing is usually considered a more comfortable way to provide the buoyancy required for a twinset. A harness configuration is popular with many twinset divers as it removes much of the clutter from the divers’ chest. If the diver is looking to progress to technical diving then they will be adding additional equipment and so streamlining the basic equipment provides a good platform for additional equipment. Unlike a traditional jacket style BCD, which surrounds the diver and provides bulk under the arms and across the chest, a harness has very little at the side or the front of the diver. Despite the additional weight, equipment and complication of a twinset the use of a harness can provide a sense of freedom and a sense of being un-encumbered that can increase the enjoyment of being in the water. Even divers who do not want to progress down the technical route often find the streamlining and freedom of a harness to be a welcome change. Harnesses come in different styles, from the minimalist single piece harness to the highly complex harness ‘systems’. A simplistic webbing harness has a number of advantages in that it reduces the clutter on the divers’ chest and can easily be adjusted to fit any size. A more complex harness means that the sizing and the configuration of clips buckles and d-rings is also more complex. Harness systems are also considerably more expansive than a simplistic harness. There are many discussions about the merits of single piece harnesses versus a harness with a break. At times it almost approaches the intensity of a holy war. On one side there are arguments that a single piece harness is very difficult to get out of, whilst on the other side there are arguments that any break in a harness is a potential failure point. Both arguments have their pros and cons. The ideal solution will depend very much on the type of diving you do. Club based diving on a RIB or shore dives have one set of considerations whilst technical dives using a hardboat will have a different set of considerations. Despite arguments to the contrary a single piece harness can be used quite successfully for UK RIB diving but for many people the advantage of a break added to the minimal risk of a failure of the break point makes it a preferable option for some types of diving. For others even the very small the risk of the break point failing is too high to justify the flexibility it might provide.   Despite the increased comfort and freedom of a harness one of the main disadvantages is the lack of storage space. Unlike a traditional BCD, with its convenient storage pockets, most harnesses do not have any storage pockets. This can lead to the situation where the diver adds additional clutter by clipping on various pieces of equipment as they do not have any storage space. With harnesses it is possible to add on pouches and pockets whilst other divers will prefer to large thigh pockets on their dry suits. In the same way that a twinset does not automatically mean a wing and harness the opposite is also true. A wing and harness can just as easily be used on a single cylinder as on a twinset. Rather than switching from a wing and harness when using a twinset to a jacket style BCD when using a single many divers will have a single cylinder wing and harness. This allows the same kit configuration irrespective of the cylinders being used. The above article was written by Mark Powel, one of only a few full time Technical Instructors in the UK. If you would like to discuss any aspects of Technical training with Mark, please contact him direct on 07770 864327.