ABOUT BUOYANCY CONTROL EQUIPMENT
Our Advice: Stainless steel backplate, properly sized wing, single piece harness with sliding HARPA hooks, crotch strap
Should I use a backplate and wing or BCD?
Reliability, durability, and modularity guarantee the backplate and wing (BPW) will always be superior to BCD designs. The BPW is simple: a length of webbing threaded through a pressed metal plate and attached to a protected bladder. We recommend a BPW for all backmounted diving, which includes a standard single tank recreational setup.
If any component wears out or is damaged, you can just replace that component. You can also swap only those components you need to change between different equipment configurations (e.g. the same backplate and harness can used for both recreational and technical/CCR dives by replacing only the wing).
How do I choose the right wing?
The wing is probably the only component you will change through your career. The wing threads onto the tank bolts between your tanks and backplate.
As a new diver the single tank setup is the most suitable choice because it is light, simple, and enjoyable to dive. As you progress you may progress to the heavier twin tank/CCR setup needing a larger wing. The best part is you can easily and quickly change it back to a single tank rig if you so desire.
Modern wings are a 360 degree “doughnut” design, allowing the free movement of air around the bladder while remaining in trim. Getting your weighting right and correctly sizing your wing will avoid excess drag.
The table below is a guide to selecting the right size wing for your configuration of cylinders and wetsuit.
| Tank Size |
Single Tank Wing Size |
Twinset Wing Size |
| 10.5 litre (80 cuft) |
12.7kg | 28lb |
17.2-18.1kg | 38-40lb |
| 12.2 litre (100 cuft) |
12.7kg | 28lb |
17.2-18.1kg | 38-40lb |
| 15 litre (120 cuft) |
16.3kg | 36lb |
24.9kg | 55lb |
| 18 litre (150 cuft) |
16.3kg | 36lb |
24.9kg | 55lb |
What not to use:
Traditional wings are large, horseshoe shaped, and may use elastic bungees to keep them streamlined. The large size is unnecessary and creates excess drag. The horseshoe shape does not allow the free movement of air and forces the diver out of ideal trim to dump gas. The elastic bungees partly solve the drag issue but introduce a new “automatic deflate” problem if you get a puncture.
How do I choose the right backplate?
The backplate is curved to comfortably sit on your back, distributing the weight to areas best able to support it. Your main decision is what material will meet buoyancy and travel requirements.
Stainless steel backplates are heavy and substitute for some of the weight a positively buoyant (underweighted or too light) diver would otherwise need to carry. They are useful to compensate for a thick wetsuit or drysuit, but use a lot of airline baggage allowance. You can get stainless steel backplates in 3mm | 0.118in (2.8kg | 6.2lb) and 6mm | 0.236in (5.5kg | 12.1lb) variants. Most divers only ever need the thinner version.
Aluminium (0.85kg | 1.87lb) and titanium backplates are lightweight, and come into their own for diving in the tropics, where not a lot of weight is required to counter thin wetsuits or skin in warm water. They also help with reducing the weight of a negatively buoyant (overweighted or too heavy) diver. They also save precious weight in your airline baggage when travelling, quickly paying for themselves in reduced excess baggage fees.
Harness
The harness threads through the backplate and rests over your shoulders and around your waist to keep the setup secure while allowing freedom of movement. Most divers wear a wetsuit or drysuit which is ample “padding” between you and the harness. However, many divers find a backplate and harness perfectly comfortable in just a Rash Vest to prevent chaffing.
Experienced divers know that harnesses with clips and buckles fail or become damaged, usually at the most inconvenient time. The most reliable system is a continuous weave harness that has no buckles and only a single stainless steel belt buckle, with a system to allow smooth adjustability (such as the
Agir Brokk HARPA Harness) for getting in and out of your gear.
Accessories
Try to limit the amount of “danglies” on your setup as these are entanglement hazards and generally make finding things harder.
D-rings – A well setup BPW only needs 5 D-rings. They are one on each shoulder for accessories and stage cylinders, one on the left hip for stage cylinders, one on the back of the crotch strap for Reels etc., and one front of the crotch strap for the Scooter tow point. What else could you want to dangle off your harness?
Crotch Strap – Stops your rig from riding up and moving around on your back, and places necessary d-rings.
Single Tank Adapter (“STA”) – For a twinset the bankplate is connected by bolts to the twin-cylinders. For a single tank the backplate is connected by bolts to the STA with the wing sandwiched between. The STA provides the cam bands to secure the single tank.
ACHIEVING IDEAL TRIM
What is ideal trim? Why is ideal trim important?
Ideal trim is diving in a horizontal position with your body parallel to the floor whilst presenting the minimum amount of physical resistance to the water ahead of you as you move through it.
Diver 1 shows commonly observed trim and how much of the body area is presented to the water as the diver moves forward.
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Diver 2 shows ideal trim position and presents substantially less resistance to the force of water as they move forward.
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The benefits of ideal trim include:
• Less gas usage throughout the dive,
• Able to move quicker through the water with less effort,
• Able to turn around quicker,
• Less silt disturbance and reef damage as fin wash is not pushed towards the floor, and
• Better general visibility of your surroundings in all directions.
Ideal trim needs a combination of diving technique and equipment set?up. When achieved it is easy to maintain with little effort.
How do you achieve ideal trim? Equipment setup:
You can conducting a balance test by starting in a horizontal position and staying perfectly still. With the assistance of your buddy note whether you tip forward, stay perfectly level, or tip backward.
To achieve ideal trim you need to setup your equipment to evenly distribute your weight. If you tip forward (are head heavy) it is because your centre of gravity is too far forward.
Tanks have a high centre of gravity because the top shoulder curve is thicker than the walls, plus more weight is added by the valve, manifold and regulator. When setting up a twinset, the top tank band should be mounted as high as possible (which is just before the tank shoulder curve) to move the tank’s centre of gravity lower.
The position of the tanks will have a large effect of your centre of gravity. If you are head heavy then you can shift the tank’s centre of gravity down by (a) for a single tank rig moving the tank band further up the tank, and (b) for technical equipment using the lower holes on the backplate for mounting to the bolts. Use the reverse if you are feet heavy.
Other options to adjust your centre of gravity include:
* Choosing negatively buoyant, neutral, or positively buoyant fins as needed (most divers use negatively buoyant 'old style' rubber fins to compensate for being slightly head heavy);
* Ankle weights should be avoided as they reduce finning efficiency whilst increasing muscle fatigue;
* Stainless steel backplates and v-block weights add negative buoyancy while evenly distributing the weight; and
* Mounting weights to the bottom of your tanks is a good option if you already need the extra weight, otherwise it is a poor solution.
How do you achieve ideal trim? Diving technique:
Some techniques for achieving ideal horizontal trim are to:
• Keep your head up with your eyes looking in a forward position, remember your body follows your eyes;
• Contracting the lower lumbar region (arching your back) and gluteus?maximus muscles (buttocks) to ensure your knees are level with your torso; and
• Keep your fins flat and parallel with your torso to ensure they assist with control and stability.
This does take work to maintain and can cause a slight aching in the lower lumbar region after the dive until your muscles become used to holding the position.
If you are head heavy, you can extend you feet out and move your arm position back to change your centre of balance point. Equally, if you are feet heavy, you can tuck your legs up a little and extend your arms forward.
What else affects trim?
Using your drysuit as you main point of lift has an impact on trim. A drysuit will tend to collect gas in the shoulder region and make your feet drop down. A wing is designed to sit under your tanks and lift them evenly without automatically dumping gas like a drysuit can. Use your wing as your primary lift device. Put only enough gas in your drysuit to allow you to be warm whilst having a full range of movement.
Tight undergarments and tight drysuits can make a diver need to compensate by having to add too much gas during the dive to be able to move freely. Check these are fitting correctly on dry land whilst not wearing tanks or a harness, by squatting down on the ground and reaching behind your back. Any tight areas around the knees or arms will be worse on the dive.
Task loading the diver will virtually always compromise their trim position with the knees dropping and fin wash hitting the floor. Staying higher in the water column can help minimise this situation.
Are there times when you need to drop out of trim?
Yes, there are times and places where dropping out of trim makes perfect sense. When you are motionless on deco, dropping out of trim may be a little more comfortable. When you are moving in a narrow inclined passage, you need to maintain trim relative to the passage floor rather than maintain an actual horizontal position.
