Buoyancy and Trim the perfect balance:
Even though body positioning in the water is a topic in all entry-level diving courses it is something that is either completely overlooked or at best briefly discussed. This is my take on configuring recreational equipment to get the most out of diving.
Firstly we should look at the difference between buoyancy and trim. These two words are related and for many of us they are synonymous. When buoyancy is being discussed we refer to a divers ability to remain neutrally buoyant in the water column. Trim on the other hand refers to a divers “attitude” in the water in relation to the bottom or a ceiling overhead. Both skills are something that you can master only by proper training and hard work.
By maintaining proper trim you greatly reduce your effort underwater. By streamlining your body you create less drag and resistance while swimming. This in turn will reflect on your aquatic comfort level and gas consumption. This will help you achieve longer and more enjoyable dives. This is the reason we started diving in the first place, to have fun exploring the underwater realm.
Were to start then? Well, not all equipment is ideal for diving in the most efficient way. The first piece of equipment that should be addressed is the BCD. The most common BCD is the jacket style BC. With this design most of the lift is distributed towards the upper part of the body. This together with the location of your lungs will most certainly make you swim in a feet down position. Since there is most of the time no crotch strap the BC will tend to move even higher up on the body making proper trim very hard to achieve. Jacket style BC´s are also not very streamlined. Big pockets on the side together with quick adjustable straps and several D-rings at unnecessary locations do not only increase drag but they also pose a serious entanglement risk.
Another thing that will effect your trim is how high up your tank is located. Many times I see divers with their cambands set to just below the cylinder neck. Not only is there a risk of loosing your tank upon entry but the weight distribution is also a concern. The heaviest part of the tank is the valve, if this is set to low all that weight is shifted down towards the lower part of the body, resulting in a feet down position. When I´m diving in a conventional jacket style BC I loosen my shoulder straps so that the dump valve and inflator hose is located on my back rather then over my shoulders. Not only will this allow me to dump gas while in proper trim but it will also allow me to move the tank up a lot higher. When I dive I will have my neck resting towards the first stage and valve. In my opinion, this is how high up the tank really should be placed. In the beginning it might be a wee bit uncomfortable but it is something you’ll get used to very quickly.
Most divers will have to wear some kind of weight system. The most common is the weightbelt. Often they slide down over your hips greatly shifting the attitude in the water. I prefer to have mine as high up as possible, just under my ribs. The belt it self will most likely be underneath the cumberbund of the BC but as long as the loose strap is long enough to be visible and easy to release I think that the pros highly outweigh the cons. Some might say that the ability to quickly ditch weight is compromised. However, if you are properly weighted this should not be much of a concern.
I prefer diving with Apeks backplate, harness and wing. The backplate and wing combination will provide lift were you want it, nicely distributed around your back. Depending on what type of cylinder that you are diving with will determine whether to use a stainless steel or aluminum backplate. Diving in the tropics with a thin wetsuit and AL S80 cylinder most people would be just fine with stainless steel plate and no additional weights. If thicker exposure suits are used a V-weight, weighted single tank adaptor or active control ballast system would take care of this. There are many benefits of diving with a backplate. The crotch strap for one will prevent the unit riding up as previously discussed. The harness is a single piece of 2” webbing will give less failure points and greatly reduce drag by keeping your chest clutter free. 2 D-rings should be placed on your chest and one on the left side of your hip. The crotch strap should have two, one on the back for clipping of reels and one in the front which is only meant to be used together with a “tow behind” scooter.
A lot of divers out there consider this to be tech specific concerns, I however like to look at it as just diving. You don’t need a certain number of dives to start improving your skill level. The sooner you start practicing and assessing your self the sooner you will be able to enjoy spending your days underwater a bit more. Your dive buddies and the aquatic environment will definitely appreciate it!