Used for buoyancy control by divers, a variety of buoyancy systems are popularly called Jackets but, to be precise, they are buoyancy systems based on a bag with a low-pressure inflators and only some of them are Jackets.
Depending on the design and purpose, they can be:
- Jackets
- Wings
- Sidemount bags
It is also possible, especially in colloquial Polish diving language, to meet with the abbreviation of the English term – BCD (Buoyancy Control Device).
Its Polish equivalent, albeit outside the literature in practice, is not used:
KRW (Rescue and Equalization Vest).
That is, to be precise, here we discuss a variety of displacement systems.
Displacement systems
The most common buoyancy system is a Jacket that also acts as a cylinder stretcher. That is, the Jacket is a cross between a backpack and buoyancy chambers that change volume (buoyancy) during a dive, supplemented with ballast pockets that allow convenient placement of the needed ballast both in terms of its quantity and its effect on trim.
The Jacket is a buoyancy system that is a compromise between being more difficult to get correct trim and easy to adjust to one’s body shape depending on the thickness of the wetsuit one is using in a given dive.
When we choose a buoyancy system for ourselves, we need to decide what configuration we want to dive in because the choice most depends on the configuration. When we buy an automatic machine we can most often adapt it to any configuration by changing, for example, the arrangement of medium-pressure lines. However, it is different with the buoyancy system. The jacket will not work well with either a sidemount or a twine and the wing from the sidemount is not suitable for a single cylinder stretcher. Of course, sometimes versatility will take priority and there are systems (hybrids) but it is with them as with any compromise. Compromise is a great solution for reasonable people but fanatics know that compromise is a failure for both sides.
Types of buoyancy systems and their features (whether these are advantages or disadvantages depends on our needs)
Jacket which is a combination of a cylinder stretcher with a buoyancy bag and usually ballast pockets. A typical Jacket has air chambers blowing at both the back and sides of the diver. This results in good maintenance of the diver on the surface and worse maintenance of trim in a horizontal position underwater.
Hybrid (Wing – Jacket) is a harness and ballast pockets as with the Jacket but the buoyancy chambers are located only at the rear as in the wing.
Wing or buoyancy system in which the bag is shaped like a horseshoe or oval tire placed on the back. The whole thing is held on the back by a harness.
The wings may differ because of the harness used and whether or not the wing itself is held in place with rubbers.
Harnesses can be full, unbuckled or pulled – so-called transpacks.
Sidemount bag, which is a buoyancy system in the form of a bag attached to the diver’s waist so that it takes up as little space as possible and stands out as little as possible when swimming through a constriction.
Difficult choices
Which buoyancy system you use depends on what you need underwater. Typical Jacket is the most versatile when it comes to fitting different thicknesses of foam. Jackets also have the best ballast pockets that make it easy to deploy ballast but also easy to shed it.
However, it has two less well-liked features. First, the location of the air chambers. A typical Jacket blows on the back and sides, a Wing only on the back. When we look at the diver hanging horizontally the air in the Jacket is lower, more on the sides and the air in the Wing is higher (near the contact of the cylinder with the back or on the sides of the cylinder). For this reason:
The wing makes it easier to maintain a horizontal position (the center of buoyancy is located higher) for that, releasing air from the wing requires a higher lift of the inflator. It also causes the diver to lie deeper in the water when swimming on his belly on the surface.
In general, the differences are not great, and whether one chooses a Wing or a Jacket from the point of view of buoyancy does not change much. In addition, when we dive in a dry suit with a single cylinder we do not blow the Jacket underwater at all, so the problem only applies to diving in a foam.
As for typical Wings with harnesses, we have a choice between those with and without rubbers. The advantage of rubbers at the wings is that we can change the trim by forcing the top or bottom of the wing to inflate more. That is, if with a given distribution of ballast you are flying slightly on your face underwater, you tie the rubbers at the bottom more tightly and those at the top more loosely. If the legs are flying the other way around, tie the ones on top tighter and the ones on the bottom looser.
Of course, you can move the ballast instead of combining with rubber bands, but some people prefer it that way and secondly, sometimes on trips we don’t have the ballast we want but a combined one and moving the center of buoyancy of the wing can be useful.
With a wing with rubbers, there is a little more work to prepare it for our needs. First, we tie all the rubber bands loosely and go for a dive. After the dive, we evaluate ourselves as it was at the beginning and end of the dive (with an empty cylinder, twine). Then we combine with rubber bands. Proper stretching of the tied elastics causes the air in the wing to move (front to back) and changes in trim. Under the water, the partner observes or we ourselves “macerate” our wing to see if, with a given amount of air, the difference in the bonding of the rubber bands (tight-loose) is sufficient to get the effect you want.
The wing without rubbers has fewer elements with which we can catch on, for example, elements of the wreck. In addition, when we are laid horizontally and damage the wing less air will escape from it (the rubbers squeeze out some of the air by force through the damage).
However, the primary difference comes from the environment in which we dive. People diving in the sea where the wave at the surface and vertical currents near the walls may force the use of large capacity bags are more likely to use bags with rubbers because such large bags work badly without rubbers. Divers diving in caves or inside wrecks don’t need such large wings so they use the smaller ones that don’t require rubbers and at the same time don’t create opportunities for hooking with them.
An important decision is the question of harnesses. We can choose from a typical Jacket one, i.e. an unzipped one with ballast pockets, and three related to the Wings, i.e. an adjustable one with ballast pockets (like the Jacket), an unzipped one with (with a hook) and an unzipped one (made of one piece of webbing).
With a single cylinder (especially when diving in a foam), it is very important from the point of view of safety to be able to get rid of some or all of the ballast underwater. As of yet, there are no really well-solved ballast pockets for wing harnesses. The principle is simple – as the ballast is easy to shed it is unfortunately easy to lose it, but it is not dangerous. What we have with Jackets doesn’t get lost all that often and allows you to drop ballast in one motion without unfastening some intermediate buckles, etc. We just pull and drop.
For the twine, a plate with an expandable harness. The unzipping is so that it is easier and quicker to get the equipment off after the dive. We always have time when dressing and certainly 30 seconds of slower dressing does not affect the diving plan. The situation is completely different after the dive. The unzipping is to make it easier (faster) to undress especially when there is little space, the dive boat sways or one hand is busy holding something (ladder, equipment, partner). In general, it is the case that people who have a harness that is not unbuckled can do very well on a bench on the edge of a quarry or on a boat when there is plenty of room. However, from observing many divers at very different dive sites, there is one conclusion. A person having a harness of one piece at the time of undress needs for a while: some space, peace and quiet, and not too much support for others at this point and rather himself often needs support (hold my camera, me, etc.). If she is on a wave in the water (in the current) next to the swaying side of a pontoon or boat and has to dismount, it either takes her longer or takes more attention each time and in fact both.
With a twine, the issue of ballast is less important because we have less of it and permanently attaching it is often more important than quickly shedding it.
With the buoyancy system for Sidemount gear, it’s so much simpler because it’s a very specialized system so the only decisions are whether you have an adjustable harness or one made of one piece. Sidemount divers mostly choose full harnesses but sidemount divers are a separate topic….
